diff -r 0019ebf76e10 -r 2c392f61f400 ProgTutorial/Essential.thy --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/ProgTutorial/Essential.thy Thu Nov 19 17:48:44 2009 +0100 @@ -0,0 +1,2359 @@ +theory Essential +imports Base FirstSteps +begin + +(*<*) +setup{* +open_file_with_prelude + "Esseantial_Code.thy" + ["theory General", "imports Base FirstSteps", "begin"] +*} +(*>*) + + +chapter {* Isabelle Essentials *} + +text {* + Isabelle is build around a few central ideas. One central idea is the + LCF-approach to theorem proving where there is a small trusted core and + everything else is build on top of this trusted core + \cite{GordonMilnerWadsworth79}. The fundamental data + structures involved in this core are certified terms and certified types, + as well as theorems. +*} + + +section {* Terms and Types *} + +text {* + In Isabelle, there are certified terms and uncertified terms (respectively types). + Uncertified terms are often just called terms. One way to construct them is by + using the antiquotation \mbox{@{text "@{term \}"}}. For example + + @{ML_response [display,gray] +"@{term \"(a::nat) + b = c\"}" +"Const (\"op =\", \) $ + (Const (\"HOL.plus_class.plus\", \) $ \ $ \) $ \"} + + constructs the term @{term "(a::nat) + b = c"}. The resulting term is printed using + the internal representation corresponding to the datatype @{ML_type_ind "term"}, + which is defined as follows: +*} + +ML_val %linenosgray{*datatype term = + Const of string * typ +| Free of string * typ +| Var of indexname * typ +| Bound of int +| Abs of string * typ * term +| $ of term * term *} + +text {* + This datatype implements Church-style lambda-terms, where types are + explicitly recorded in variables, constants and abstractions. As can be + seen in Line 5, terms use the usual de Bruijn index mechanism for + representing bound variables. For example in + + @{ML_response_fake [display, gray] + "@{term \"\x y. x y\"}" + "Abs (\"x\", \"'a \ 'b\", Abs (\"y\", \"'a\", Bound 1 $ Bound 0))"} + + the indices refer to the number of Abstractions (@{ML Abs}) that we need to + skip until we hit the @{ML Abs} that binds the corresponding + variable. Constructing a term with dangling de Bruijn indices is possible, + but will be flagged as ill-formed when you try to typecheck or certify it + (see Section~\ref{sec:typechecking}). Note that the names of bound variables + are kept at abstractions for printing purposes, and so should be treated + only as ``comments''. Application in Isabelle is realised with the + term-constructor @{ML $}. + + Isabelle makes a distinction between \emph{free} variables (term-constructor + @{ML Free} and written on the user level in blue colour) and + \emph{schematic} variables (term-constructor @{ML Var} and written with a + leading question mark). Consider the following two examples + + @{ML_response_fake [display, gray] +"let + val v1 = Var ((\"x\", 3), @{typ bool}) + val v2 = Var ((\"x1\", 3), @{typ bool}) + val v3 = Free (\"x\", @{typ bool}) +in + string_of_terms @{context} [v1, v2, v3] + |> tracing +end" +"?x3, ?x1.3, x"} + + When constructing terms, you are usually concerned with free variables (as + mentioned earlier, you cannot construct schematic variables using the + antiquotation @{text "@{term \}"}). If you deal with theorems, you have to, + however, observe the distinction. The reason is that only schematic + variables can be instantiated with terms when a theorem is applied. A + similar distinction between free and schematic variables holds for types + (see below). + + \begin{readmore} + Terms and types are described in detail in \isccite{sec:terms}. Their + definition and many useful operations are implemented in @{ML_file "Pure/term.ML"}. + For constructing terms involving HOL constants, many helper functions are defined + in @{ML_file "HOL/Tools/hologic.ML"}. + \end{readmore} + + Constructing terms via antiquotations has the advantage that only typable + terms can be constructed. For example + + @{ML_response_fake_both [display,gray] + "@{term \"x x\"}" + "Type unification failed: Occurs check!"} + + raises a typing error, while it perfectly ok to construct the term + + @{ML_response_fake [display,gray] +"let + val omega = Free (\"x\", @{typ \"nat \ nat\"}) $ Free (\"x\", @{typ nat}) +in + tracing (string_of_term @{context} omega) +end" + "x x"} + + with the raw ML-constructors. + + Sometimes the internal representation of terms can be surprisingly different + from what you see at the user-level, because the layers of + parsing/type-checking/pretty printing can be quite elaborate. + + \begin{exercise} + Look at the internal term representation of the following terms, and + find out why they are represented like this: + + \begin{itemize} + \item @{term "case x of 0 \ 0 | Suc y \ y"} + \item @{term "\(x,y). P y x"} + \item @{term "{ [x::int] | x. x \ -2 }"} + \end{itemize} + + Hint: The third term is already quite big, and the pretty printer + may omit parts of it by default. If you want to see all of it, you + can use the following ML-function to set the printing depth to a higher + value: + + @{ML [display,gray] "print_depth 50"} + \end{exercise} + + The antiquotation @{text "@{prop \}"} constructs terms by inserting the + usually invisible @{text "Trueprop"}-coercions whenever necessary. + Consider for example the pairs + +@{ML_response [display,gray] "(@{term \"P x\"}, @{prop \"P x\"})" +"(Free (\"P\", \) $ Free (\"x\", \), + Const (\"Trueprop\", \) $ (Free (\"P\", \) $ Free (\"x\", \)))"} + + where a coercion is inserted in the second component and + + @{ML_response [display,gray] "(@{term \"P x \ Q x\"}, @{prop \"P x \ Q x\"})" + "(Const (\"==>\", \) $ \ $ \, + Const (\"==>\", \) $ \ $ \)"} + + where it is not (since it is already constructed by a meta-implication). + The purpose of the @{text "Trueprop"}-coercion is to embed formulae of + an object logic, for example HOL, into the meta-logic of Isabelle. The coercion + is needed whenever a term is constructed that will be proved as a theorem. + + As already seen above, types can be constructed using the antiquotation + @{text "@{typ \}"}. For example: + + @{ML_response_fake [display,gray] "@{typ \"bool \ nat\"}" "bool \ nat"} + + The corresponding datatype is +*} + +ML_val{*datatype typ = + Type of string * typ list +| TFree of string * sort +| TVar of indexname * sort *} + +text {* + Like with terms, there is the distinction between free type + variables (term-constructor @{ML "TFree"}) and schematic + type variables (term-constructor @{ML "TVar"} and printed with + a leading question mark). A type constant, + like @{typ "int"} or @{typ bool}, are types with an empty list + of argument types. However, it needs a bit of effort to show an + example, because Isabelle always pretty prints types (unlike terms). + Using just the antiquotation @{text "@{typ \"bool\"}"} we only see + + @{ML_response [display, gray] + "@{typ \"bool\"}" + "bool"} + + that is the pretty printed version of @{text "bool"}. However, in PolyML + (version 5.3) it is easy to install your own pretty printer. With the + function below we mimic the behaviour of the usual pretty printer for + datatypes (it uses pretty-printing functions which will be explained in more + detail in Section~\ref{sec:pretty}). +*} + +ML{*local + fun pp_pair (x, y) = Pretty.list "(" ")" [x, y] + fun pp_list xs = Pretty.list "[" "]" xs + fun pp_str s = Pretty.str s + fun pp_qstr s = Pretty.quote (pp_str s) + fun pp_int i = pp_str (string_of_int i) + fun pp_sort S = pp_list (map pp_qstr S) + fun pp_constr a args = Pretty.block [pp_str a, Pretty.brk 1, args] +in +fun raw_pp_typ (TVar ((a, i), S)) = + pp_constr "TVar" (pp_pair (pp_pair (pp_qstr a, pp_int i), pp_sort S)) + | raw_pp_typ (TFree (a, S)) = + pp_constr "TFree" (pp_pair (pp_qstr a, pp_sort S)) + | raw_pp_typ (Type (a, tys)) = + pp_constr "Type" (pp_pair (pp_qstr a, pp_list (map raw_pp_typ tys))) +end*} + +text {* + We can install this pretty printer with the function + @{ML_ind addPrettyPrinter in PolyML} as follows. +*} + +ML{*PolyML.addPrettyPrinter + (fn _ => fn _ => ml_pretty o Pretty.to_ML o raw_pp_typ)*} + +text {* + Now the type bool is printed out in full detail. + + @{ML_response [display,gray] + "@{typ \"bool\"}" + "Type (\"bool\", [])"} + + When printing out a list-type + + @{ML_response [display,gray] + "@{typ \"'a list\"}" + "Type (\"List.list\", [TFree (\"'a\", [\"HOL.type\"])])"} + + we can see the full name of the type is actually @{text "List.list"}, indicating + that it is defined in the theory @{text "List"}. However, one has to be + careful with names of types, because even if + @{text "fun"}, @{text "bool"} and @{text "nat"} are defined in the + theories @{text "HOL"} and @{text "Nat"}, respectively, they are + still represented by their simple name. + + @{ML_response [display,gray] + "@{typ \"bool \ nat\"}" + "Type (\"fun\", [Type (\"bool\", []), Type (\"nat\", [])])"} + + We can restore the usual behaviour of Isabelle's pretty printer + with the code +*} + +ML{*PolyML.addPrettyPrinter + (fn _ => fn _ => ml_pretty o Pretty.to_ML o Proof_Display.pp_typ Pure.thy)*} + +text {* + After that the types for booleans, lists and so on are printed out again + the standard Isabelle way. + + @{ML_response_fake [display, gray] + "@{typ \"bool\"}; +@{typ \"'a list\"}" + "\"bool\" +\"'a List.list\""} + + \begin{readmore} + Types are described in detail in \isccite{sec:types}. Their + definition and many useful operations are implemented + in @{ML_file "Pure/type.ML"}. + \end{readmore} +*} + +section {* Constructing Terms and Types Manually\label{sec:terms_types_manually} *} + +text {* + While antiquotations are very convenient for constructing terms, they can + only construct fixed terms (remember they are ``linked'' at compile-time). + However, you often need to construct terms manually. For example, a + function that returns the implication @{text "\(x::nat). P x \ Q x"} taking + @{term P} and @{term Q} as arguments can only be written as: + +*} + +ML{*fun make_imp P Q = +let + val x = Free ("x", @{typ nat}) +in + Logic.all x (Logic.mk_implies (P $ x, Q $ x)) +end *} + +text {* + The reason is that you cannot pass the arguments @{term P} and @{term Q} + into an antiquotation.\footnote{At least not at the moment.} For example + the following does \emph{not} work. +*} + +ML{*fun make_wrong_imp P Q = @{prop "\(x::nat). P x \ Q x"} *} + +text {* + To see this, apply @{text "@{term S}"} and @{text "@{term T}"} + to both functions. With @{ML make_imp} you obtain the intended term involving + the given arguments + + @{ML_response [display,gray] "make_imp @{term S} @{term T}" +"Const \ $ + Abs (\"x\", Type (\"nat\",[]), + Const \ $ (Free (\"S\",\) $ \) $ (Free (\"T\",\) $ \))"} + + whereas with @{ML make_wrong_imp} you obtain a term involving the @{term "P"} + and @{text "Q"} from the antiquotation. + + @{ML_response [display,gray] "make_wrong_imp @{term S} @{term T}" +"Const \ $ + Abs (\"x\", \, + Const \ $ (Const \ $ (Free (\"P\",\) $ \)) $ + (Const \ $ (Free (\"Q\",\) $ \)))"} + + There are a number of handy functions that are frequently used for + constructing terms. One is the function @{ML_ind list_comb in Term}, which + takes as argument a term and a list of terms, and produces as output the + term list applied to the term. For example + + +@{ML_response_fake [display,gray] +"let + val trm = @{term \"P::nat\"} + val args = [@{term \"True\"}, @{term \"False\"}] +in + list_comb (trm, args) +end" +"Free (\"P\", \"nat\") $ Const (\"True\", \"bool\") $ Const (\"False\", \"bool\")"} + + Another handy function is @{ML_ind lambda in Term}, which abstracts a variable + in a term. For example + + @{ML_response_fake [display,gray] +"let + val x_nat = @{term \"x::nat\"} + val trm = @{term \"(P::nat \ bool) x\"} +in + lambda x_nat trm +end" + "Abs (\"x\", \"nat\", Free (\"P\", \"bool \ bool\") $ Bound 0)"} + + In this example, @{ML lambda} produces a de Bruijn index (i.e.~@{ML "Bound 0"}), + and an abstraction, where it also records the type of the abstracted + variable and for printing purposes also its name. Note that because of the + typing annotation on @{text "P"}, the variable @{text "x"} in @{text "P x"} + is of the same type as the abstracted variable. If it is of different type, + as in + + @{ML_response_fake [display,gray] +"let + val x_int = @{term \"x::int\"} + val trm = @{term \"(P::nat \ bool) x\"} +in + lambda x_int trm +end" + "Abs (\"x\", \"int\", Free (\"P\", \"nat \ bool\") $ Free (\"x\", \"nat\"))"} + + then the variable @{text "Free (\"x\", \"int\")"} is \emph{not} abstracted. + This is a fundamental principle + of Church-style typing, where variables with the same name still differ, if they + have different type. + + There is also the function @{ML_ind subst_free in Term} with which terms can be + replaced by other terms. For example below, we will replace in @{term + "(f::nat \ nat \ nat) 0 x"} the subterm @{term "(f::nat \ nat \ nat) 0"} by + @{term y}, and @{term x} by @{term True}. + + @{ML_response_fake [display,gray] +"let + val sub1 = (@{term \"(f::nat \ nat \ nat) 0\"}, @{term \"y::nat \ nat\"}) + val sub2 = (@{term \"x::nat\"}, @{term \"True\"}) + val trm = @{term \"((f::nat \ nat \ nat) 0) x\"} +in + subst_free [sub1, sub2] trm +end" + "Free (\"y\", \"nat \ nat\") $ Const (\"True\", \"bool\")"} + + As can be seen, @{ML subst_free} does not take typability into account. + However it takes alpha-equivalence into account: + + @{ML_response_fake [display, gray] +"let + val sub = (@{term \"(\y::nat. y)\"}, @{term \"x::nat\"}) + val trm = @{term \"(\x::nat. x)\"} +in + subst_free [sub] trm +end" + "Free (\"x\", \"nat\")"} + + Similarly the function @{ML_ind subst_bounds in Term}, replaces lose bound + variables with terms. To see how this function works, let us implement a + function that strips off the outermost quantifiers in a term. +*} + +ML{*fun strip_alls t = +let + fun aux (x, T, t) = strip_alls t |>> cons (Free (x, T)) +in + case t of + Const ("All", _) $ Abs body => aux body + | _ => ([], t) +end*} + +text {* + The function returns a pair consisting of the stripped off variables and + the body of the universal quantification. For example + + @{ML_response_fake [display, gray] + "strip_alls @{term \"\x y. x = (y::bool)\"}" +"([Free (\"x\", \"bool\"), Free (\"y\", \"bool\")], + Const (\"op =\", \) $ Bound 1 $ Bound 0)"} + + After calling @{ML strip_alls}, you obtain a term with lose bound variables. With + the function @{ML subst_bounds}, you can replace these lose @{ML_ind + Bound in Term}s with the stripped off variables. + + @{ML_response_fake [display, gray, linenos] + "let + val (vrs, trm) = strip_alls @{term \"\x y. x = (y::bool)\"} +in + subst_bounds (rev vrs, trm) + |> string_of_term @{context} + |> tracing +end" + "x = y"} + + Note that in Line 4 we had to reverse the list of variables that @{ML + strip_alls} returned. The reason is that the head of the list the function + @{ML subst_bounds} takes is the replacement for @{ML "Bound 0"}, the next + element for @{ML "Bound 1"} and so on. + + Notice also that this function might introduce name clashes, since we + substitute just a variable with the name recorded in an abstraction. This + name is by no means unique. If clashes need to be avoided, then we should + use the function @{ML_ind dest_abs in Term}, which returns the body where + the lose de Bruijn index is replaced by a unique free variable. For example + + + @{ML_response_fake [display,gray] + "let + val body = Bound 0 $ Free (\"x\", @{typ nat}) +in + Term.dest_abs (\"x\", @{typ \"nat \ bool\"}, body) +end" + "(\"xa\", Free (\"xa\", \"nat \ bool\") $ Free (\"x\", \"nat\"))"} + + There are also many convenient functions that construct specific HOL-terms + in the structure @{ML_struct HOLogic}. For + example @{ML_ind mk_eq in HOLogic} constructs an equality out of two terms. + The types needed in this equality are calculated from the type of the + arguments. For example + +@{ML_response_fake [gray,display] +"let + val eq = HOLogic.mk_eq (@{term \"True\"}, @{term \"False\"}) +in + string_of_term @{context} eq + |> tracing +end" + "True = False"} +*} + +text {* + \begin{readmore} + There are many functions in @{ML_file "Pure/term.ML"}, @{ML_file + "Pure/logic.ML"} and @{ML_file "HOL/Tools/hologic.ML"} that make manual + constructions of terms and types easier. + \end{readmore} + + When constructing terms manually, there are a few subtle issues with + constants. They usually crop up when pattern matching terms or types, or + when constructing them. While it is perfectly ok to write the function + @{text is_true} as follows +*} + +ML{*fun is_true @{term True} = true + | is_true _ = false*} + +text {* + this does not work for picking out @{text "\"}-quantified terms. Because + the function +*} + +ML{*fun is_all (@{term All} $ _) = true + | is_all _ = false*} + +text {* + will not correctly match the formula @{prop[source] "\x::nat. P x"}: + + @{ML_response [display,gray] "is_all @{term \"\x::nat. P x\"}" "false"} + + The problem is that the @{text "@term"}-antiquotation in the pattern + fixes the type of the constant @{term "All"} to be @{typ "('a \ bool) \ bool"} for + an arbitrary, but fixed type @{typ "'a"}. A properly working alternative + for this function is +*} + +ML{*fun is_all (Const ("All", _) $ _) = true + | is_all _ = false*} + +text {* + because now + +@{ML_response [display,gray] "is_all @{term \"\x::nat. P x\"}" "true"} + + matches correctly (the first wildcard in the pattern matches any type and the + second any term). + + However there is still a problem: consider the similar function that + attempts to pick out @{text "Nil"}-terms: +*} + +ML{*fun is_nil (Const ("Nil", _)) = true + | is_nil _ = false *} + +text {* + Unfortunately, also this function does \emph{not} work as expected, since + + @{ML_response [display,gray] "is_nil @{term \"Nil\"}" "false"} + + The problem is that on the ML-level the name of a constant is more + subtle than you might expect. The function @{ML is_all} worked correctly, + because @{term "All"} is such a fundamental constant, which can be referenced + by @{ML "Const (\"All\", some_type)" for some_type}. However, if you look at + + @{ML_response [display,gray] "@{term \"Nil\"}" "Const (\"List.list.Nil\", \)"} + + the name of the constant @{text "Nil"} depends on the theory in which the + term constructor is defined (@{text "List"}) and also in which datatype + (@{text "list"}). Even worse, some constants have a name involving + type-classes. Consider for example the constants for @{term "zero"} and + \mbox{@{text "(op *)"}}: + + @{ML_response [display,gray] "(@{term \"0::nat\"}, @{term \"(op *)\"})" + "(Const (\"HOL.zero_class.zero\", \), + Const (\"HOL.times_class.times\", \))"} + + While you could use the complete name, for example + @{ML "Const (\"List.list.Nil\", some_type)" for some_type}, for referring to or + matching against @{text "Nil"}, this would make the code rather brittle. + The reason is that the theory and the name of the datatype can easily change. + To make the code more robust, it is better to use the antiquotation + @{text "@{const_name \}"}. With this antiquotation you can harness the + variable parts of the constant's name. Therefore a function for + matching against constants that have a polymorphic type should + be written as follows. +*} + +ML{*fun is_nil_or_all (Const (@{const_name "Nil"}, _)) = true + | is_nil_or_all (Const (@{const_name "All"}, _) $ _) = true + | is_nil_or_all _ = false *} + +text {* + The antiquotation for properly referencing type constants is @{text "@{type_name \}"}. + For example + + @{ML_response [display,gray] + "@{type_name \"list\"}" "\"List.list\""} + + \footnote{\bf FIXME: Explain the following better; maybe put in a separate + section and link with the comment in the antiquotation section.} + + Occasionally you have to calculate what the ``base'' name of a given + constant is. For this you can use the function @{ML_ind "Sign.extern_const"} or + @{ML_ind Long_Name.base_name}. For example: + + @{ML_response [display,gray] "Sign.extern_const @{theory} \"List.list.Nil\"" "\"Nil\""} + + The difference between both functions is that @{ML extern_const in Sign} returns + the smallest name that is still unique, whereas @{ML base_name in Long_Name} always + strips off all qualifiers. + + \begin{readmore} + Functions about naming are implemented in @{ML_file "Pure/General/name_space.ML"}; + functions about signatures in @{ML_file "Pure/sign.ML"}. + \end{readmore} + + Although types of terms can often be inferred, there are many + situations where you need to construct types manually, especially + when defining constants. For example the function returning a function + type is as follows: + +*} + +ML{*fun make_fun_type ty1 ty2 = Type ("fun", [ty1, ty2]) *} + +text {* This can be equally written with the combinator @{ML_ind "-->" in Term} as: *} + +ML{*fun make_fun_type ty1 ty2 = ty1 --> ty2 *} + +text {* + If you want to construct a function type with more than one argument + type, then you can use @{ML_ind "--->" in Term}. +*} + +ML{*fun make_fun_types tys ty = tys ---> ty *} + +text {* + A handy function for manipulating terms is @{ML_ind map_types in Term}: it takes a + function and applies it to every type in a term. You can, for example, + change every @{typ nat} in a term into an @{typ int} using the function: +*} + +ML{*fun nat_to_int ty = + (case ty of + @{typ nat} => @{typ int} + | Type (s, tys) => Type (s, map nat_to_int tys) + | _ => ty)*} + +text {* + Here is an example: + +@{ML_response_fake [display,gray] +"map_types nat_to_int @{term \"a = (1::nat)\"}" +"Const (\"op =\", \"int \ int \ bool\") + $ Free (\"a\", \"int\") $ Const (\"HOL.one_class.one\", \"int\")"} + + If you want to obtain the list of free type-variables of a term, you + can use the function @{ML_ind add_tfrees in Term} + (similarly @{ML_ind add_tvars in Term} for the schematic type-variables). + One would expect that such functions + take a term as input and return a list of types. But their type is actually + + @{text[display] "Term.term -> (string * Term.sort) list -> (string * Term.sort) list"} + + that is they take, besides a term, also a list of type-variables as input. + So in order to obtain the list of type-variables of a term you have to + call them as follows + + @{ML_response [gray,display] + "Term.add_tfrees @{term \"(a, b)\"} []" + "[(\"'b\", [\"HOL.type\"]), (\"'a\", [\"HOL.type\"])]"} + + The reason for this definition is that @{ML add_tfrees in Term} can + be easily folded over a list of terms. Similarly for all functions + named @{text "add_*"} in @{ML_file "Pure/term.ML"}. + + \begin{exercise}\label{fun:revsum} + Write a function @{text "rev_sum : term -> term"} that takes a + term of the form @{text "t\<^isub>1 + t\<^isub>2 + \ + t\<^isub>n"} (whereby @{text "n"} might be one) + and returns the reversed sum @{text "t\<^isub>n + \ + t\<^isub>2 + t\<^isub>1"}. Assume + the @{text "t\<^isub>i"} can be arbitrary expressions and also note that @{text "+"} + associates to the left. Try your function on some examples. + \end{exercise} + + \begin{exercise}\label{fun:makesum} + Write a function that takes two terms representing natural numbers + in unary notation (like @{term "Suc (Suc (Suc 0))"}), and produces the + number representing their sum. + \end{exercise} + + \begin{exercise}\label{ex:debruijn} + Implement the function, which we below name deBruijn, that depends on a natural + number n$>$0 and constructs terms of the form: + + \begin{center} + \begin{tabular}{r@ {\hspace{2mm}}c@ {\hspace{2mm}}l} + {\it rhs n} & $\dn$ & {\large$\bigwedge$}{\it i=1\ldots n. P\,i}\\ + {\it lhs n} & $\dn$ & {\large$\bigwedge$}{\it i=1\ldots n. P\,i = P (i + 1 mod n)} + $\longrightarrow$ {\it rhs n}\\ + {\it deBruijn n} & $\dn$ & {\it lhs n} $\longrightarrow$ {\it rhs n}\\ + \end{tabular} + \end{center} + + This function returns for n=3 the term + + \begin{center} + \begin{tabular}{l} + (P 1 = P 2 $\longrightarrow$ P 1 $\wedge$ P 2 $\wedge$ P 3) $\wedge$\\ + (P 2 = P 3 $\longrightarrow$ P 1 $\wedge$ P 2 $\wedge$ P 3) $\wedge$\\ + (P 3 = P 1 $\longrightarrow$ P 1 $\wedge$ P 2 $\wedge$ P 3) $\longrightarrow$ P 1 $\wedge$ P 2 $\wedge$ P 3 + \end{tabular} + \end{center} + + Make sure you use the functions defined in @{ML_file "HOL/Tools/hologic.ML"} + for constructing the terms for the logical connectives.\footnote{Thanks to Roy + Dyckhoff for suggesting this exercise and working out the details.} + \end{exercise} +*} + +section {* Unification and Matching *} + +text {* + As seen earlier, Isabelle's terms and types may contain schematic term variables + (term-constructor @{ML Var}) and schematic type variables (term-constructor + @{ML TVar}). These variables stand for unknown entities, which can be made + more concrete by instantiations. Such instantiations might be a result of + unification or matching. While in case of types, unification and matching is + relatively straightforward, in case of terms the algorithms are + substantially more complicated, because terms need higher-order versions of + the unification and matching algorithms. Below we shall use the + antiquotations @{text "@{typ_pat \}"} and @{text "@{term_pat \}"} from + Section~\ref{sec:antiquote} in order to construct examples involving + schematic variables. + + Let us begin with describing the unification and matching function for + types. Both return type environments (ML-type @{ML_type "Type.tyenv"}) + which map schematic type variables to types and sorts. Below we use the + function @{ML_ind typ_unify in Sign} from the structure @{ML_struct Sign} + for unifying the types @{text "?'a * ?'b"} and @{text "?'b list * + nat"}. This will produce the mapping, or type environment, @{text "[?'a := + ?'b list, ?'b := nat]"}. +*} + +ML %linenosgray{*val (tyenv_unif, _) = let + val ty1 = @{typ_pat "?'a * ?'b"} + val ty2 = @{typ_pat "?'b list * nat"} +in + Sign.typ_unify @{theory} (ty1, ty2) (Vartab.empty, 0) +end*} + +text {* + The environment @{ML_ind "Vartab.empty"} in line 5 stands for the empty type + environment, which is needed for starting the unification without any + (pre)instantiations. The @{text 0} is an integer index that will be explained + below. In case of failure @{ML typ_unify in Sign} will throw the exception + @{text TUNIFY}. We can print out the resulting type environment bound to + @{ML tyenv_unif} with the built-in function @{ML_ind dest in Vartab} from the + structure @{ML_struct Vartab}. + + @{ML_response_fake [display,gray] + "Vartab.dest tyenv_unif" + "[((\"'a\", 0), ([\"HOL.type\"], \"?'b List.list\")), + ((\"'b\", 0), ([\"HOL.type\"], \"nat\"))]"} +*} + +text_raw {* + \begin{figure}[t] + \begin{minipage}{\textwidth} + \begin{isabelle}*} +ML{*fun pretty_helper aux env = + env |> Vartab.dest + |> map ((fn (s1, s2) => s1 ^ " := " ^ s2) o aux) + |> commas + |> enclose "[" "]" + |> tracing + +fun pretty_tyenv ctxt tyenv = +let + fun get_typs (v, (s, T)) = (TVar (v, s), T) + val print = pairself (Syntax.string_of_typ ctxt) +in + pretty_helper (print o get_typs) tyenv +end*} +text_raw {* + \end{isabelle} + \end{minipage} + \caption{A pretty printing function for type environments, which are + produced by unification and matching.\label{fig:prettyenv}} + \end{figure} +*} + +text {* + The first components in this list stand for the schematic type variables and + the second are the associated sorts and types. In this example the sort is + the default sort @{text "HOL.type"}. Instead of @{ML "Vartab.dest"}, we will + use in what follows our own pretty-printing function from + Figure~\ref{fig:prettyenv} for @{ML_type "Type.tyenv"}s. For the type + environment in the example this function prints out the more legible: + + + @{ML_response_fake [display, gray] + "pretty_tyenv @{context} tyenv_unif" + "[?'a := ?'b list, ?'b := nat]"} + + The way the unification function @{ML typ_unify in Sign} is implemented + using an initial type environment and initial index makes it easy to + unify more than two terms. For example +*} + +ML %linenosgray{*val (tyenvs, _) = let + val tys1 = (@{typ_pat "?'a"}, @{typ_pat "?'b list"}) + val tys2 = (@{typ_pat "?'b"}, @{typ_pat "nat"}) +in + fold (Sign.typ_unify @{theory}) [tys1, tys2] (Vartab.empty, 0) +end*} + +text {* + The index @{text 0} in Line 5 is the maximal index of the schematic type + variables occurring in @{text tys1} and @{text tys2}. This index will be + increased whenever a new schematic type variable is introduced during + unification. This is for example the case when two schematic type variables + have different, incomparable sorts. Then a new schematic type variable is + introduced with the combined sorts. To show this let us assume two sorts, + say @{text "s1"} and @{text "s2"}, which we attach to the schematic type + variables @{text "?'a"} and @{text "?'b"}. Since we do not make any + assumption about the sorts, they are incomparable. +*} + +ML{*val (tyenv, index) = let + val ty1 = @{typ_pat "?'a::s1"} + val ty2 = @{typ_pat "?'b::s2"} +in + Sign.typ_unify @{theory} (ty1, ty2) (Vartab.empty, 0) +end*} + +text {* + To print out the result type environment we switch on the printing + of sort information by setting @{ML_ind show_sorts in Syntax} to + true. This allows us to inspect the typing environment. + + @{ML_response_fake [display,gray] + "pretty_tyenv @{context} tyenv" + "[?'a::s1 := ?'a1::{s1, s2}, ?'b::s2 := ?'a1::{s1, s2}]"} + + As can be seen, the type variables @{text "?'a"} and @{text "?'b"} are instantiated + with a new type variable @{text "?'a1"} with sort @{text "{s1, s2}"}. Since a new + type variable has been introduced the @{ML index}, originally being @{text 0}, + has been increased to @{text 1}. + + @{ML_response [display,gray] + "index" + "1"} + + Let us now return to the unification problem @{text "?'a * ?'b"} and + @{text "?'b list * nat"} from the beginning of this section, and the + calculated type environment @{ML tyenv_unif}: + + @{ML_response_fake [display, gray] + "pretty_tyenv @{context} tyenv_unif" + "[?'a := ?'b list, ?'b := nat]"} + + Observe that the type environment which the function @{ML typ_unify in + Sign} returns is in \emph{not} an instantiation in fully solved form: while @{text + "?'b"} is instantiated to @{typ nat}, this is not propagated to the + instantiation for @{text "?'a"}. In unification theory, this is often + called an instantiation in \emph{triangular form}. These triangular + instantiations, or triangular type environments, are used because of + performance reasons. To apply such a type environment to a type, say @{text "?'a * + ?'b"}, you should use the function @{ML_ind norm_type in Envir}: + + @{ML_response_fake [display, gray] + "Envir.norm_type tyenv_unif @{typ_pat \"?'a * ?'b\"}" + "nat list * nat"} + + Matching of types can be done with the function @{ML_ind typ_match in Sign} + also from the structure @{ML_struct Sign}. This function returns a @{ML_type + Type.tyenv} as well, but might raise the exception @{text TYPE_MATCH} in case + of failure. For example +*} + +ML{*val tyenv_match = let + val pat = @{typ_pat "?'a * ?'b"} + and ty = @{typ_pat "bool list * nat"} +in + Sign.typ_match @{theory} (pat, ty) Vartab.empty +end*} + +text {* + Printing out the calculated matcher gives + + @{ML_response_fake [display,gray] + "pretty_tyenv @{context} tyenv_match" + "[?'a := bool list, ?'b := nat]"} + + Unlike unification, which uses the function @{ML norm_type in Envir}, + applying the matcher to a type needs to be done with the function + @{ML_ind subst_type in Envir}. For example + + @{ML_response_fake [display, gray] + "Envir.subst_type tyenv_match @{typ_pat \"?'a * ?'b\"}" + "bool list * nat"} + + Be careful to observe the difference: use always + @{ML subst_type in Envir} for matchers and @{ML norm_type in Envir} + for unifiers. To show the difference, let us calculate the + following matcher: +*} + +ML{*val tyenv_match' = let + val pat = @{typ_pat "?'a * ?'b"} + and ty = @{typ_pat "?'b list * nat"} +in + Sign.typ_match @{theory} (pat, ty) Vartab.empty +end*} + +text {* + Now @{ML tyenv_unif} is equal to @{ML tyenv_match'}. If we apply + @{ML norm_type in Envir} to the type @{text "?'a * ?'b"} we obtain + + @{ML_response_fake [display, gray] + "Envir.norm_type tyenv_match' @{typ_pat \"?'a * ?'b\"}" + "nat list * nat"} + + which does not solve the matching problem, and if + we apply @{ML subst_type in Envir} to the same type we obtain + + @{ML_response_fake [display, gray] + "Envir.subst_type tyenv_unif @{typ_pat \"?'a * ?'b\"}" + "?'b list * nat"} + + which does not solve the unification problem. + + \begin{readmore} + Unification and matching for types is implemented + in @{ML_file "Pure/type.ML"}. The ``interface'' functions for them + are in @{ML_file "Pure/sign.ML"}. Matching and unification produce type environments + as results. These are implemented in @{ML_file "Pure/envir.ML"}. + This file also includes the substitution and normalisation functions, + which apply a type environment to a type. Type environments are lookup + tables which are implemented in @{ML_file "Pure/term_ord.ML"}. + \end{readmore} +*} + +text {* + Unification and matching of terms is substantially more complicated than the + type-case. The reason is that terms have abstractions and, in this context, + unification or matching modulo plain equality is often not meaningful. + Nevertheless, Isabelle implements the function @{ML_ind + first_order_match in Pattern} for terms. This matching function returns a + type environment and a term environment. To pretty print the latter we use + the function @{text "pretty_env"}: +*} + +ML{*fun pretty_env ctxt env = +let + fun get_trms (v, (T, t)) = (Var (v, T), t) + val print = pairself (string_of_term ctxt) +in + pretty_helper (print o get_trms) env +end*} + +text {* + As can be seen from the @{text "get_trms"}-function, a term environment associates + a schematic term variable with a type and a term. An example of a first-order + matching problem is the term @{term "P (\a b. Q b a)"} and the pattern + @{text "?X ?Y"}. +*} + +ML{*val (_, fo_env) = let + val fo_pat = @{term_pat "(?X::(nat\nat\nat)\bool) ?Y"} + val trm_a = @{term "P::(nat\nat\nat)\bool"} + val trm_b = @{term "\a b. (Q::nat\nat\nat) b a"} + val init = (Vartab.empty, Vartab.empty) +in + Pattern.first_order_match @{theory} (fo_pat, trm_a $ trm_b) init +end *} + +text {* + In this example we annotated explicitly types because then + the type environment is empty and can be ignored. The + resulting term environment is + + @{ML_response_fake [display, gray] + "pretty_env @{context} fo_env" + "[?X := P, ?Y := \a b. Q b a]"} + + The matcher can be applied to a term using the function @{ML_ind subst_term + in Envir} (remember the same convention for types applies to terms: @{ML + subst_term in Envir} is for matchers and @{ML norm_term in Envir} for + unifiers). The function @{ML subst_term in Envir} expects a type environment, + which is set to empty in the example below, and a term environment. + + @{ML_response_fake [display, gray] + "let + val trm = @{term_pat \"(?X::(nat\nat\nat)\bool) ?Y\"} +in + Envir.subst_term (Vartab.empty, fo_env) trm + |> string_of_term @{context} + |> tracing +end" + "P (\a b. Q b a)"} + + First-order matching is useful for matching against applications and + variables. It can deal also with abstractions and a limited form of + alpha-equivalence, but this kind of matching should be used with care, since + it is not clear whether the result is meaningful. A meaningful example is + matching @{text "\x. P x"} against the pattern @{text "\y. ?X y"}. In this + case, first-order matching produces @{text "[?X := P]"}. + + @{ML_response_fake [display, gray] + "let + val fo_pat = @{term_pat \"\y. (?X::nat\bool) y\"} + val trm = @{term \"\x. (P::nat\bool) x\"} + val init = (Vartab.empty, Vartab.empty) +in + Pattern.first_order_match @{theory} (fo_pat, trm) init + |> snd + |> pretty_env @{context} +end" + "[?X := P]"} +*} + +text {* + Unification of abstractions is more thoroughly studied in the context + of higher-order pattern unification and higher-order pattern matching. A + \emph{\index*{pattern}} is an abstraction term whose ``head symbol'' (that is the + first symbol under an abstraction) is either a constant, a schematic or a free + variable. If it is a schematic variable then it can be only applied with + distinct bound variables. This excludes terms where a schematic variable is an + argument of another one and where a schematic variable is applied + twice with the same bound variable. The function @{ML_ind pattern in Pattern} + in the structure @{ML_struct Pattern} tests whether a term satisfies these + restrictions. + + @{ML_response [display, gray] + "let + val trm_list = + [@{term_pat \"?X\"}, @{term_pat \"a\"}, + @{term_pat \"\a b. ?X a b\"}, @{term_pat \"\a b. (op +) a b\"}, + @{term_pat \"\a. (op +) a ?Y\"}, @{term_pat \"?X ?Y\"}, + @{term_pat \"\a b. ?X a b ?Y\"}, @{term_pat \"\a. ?X a a\"}] +in + map Pattern.pattern trm_list +end" + "[true, true, true, true, true, false, false, false]"} + + The point of the restriction to patterns is that unification and matching + are decidable and produce most general unifiers, respectively matchers. + In this way, matching and unification can be implemented as functions that + produce a type and term environment (unification actually returns a + record of type @{ML_type Envir.env} containing a maxind, a type environment + and a term environment). The corresponding functions are @{ML_ind match in Pattern}, + and @{ML_ind unify in Pattern} both implemented in the structure + @{ML_struct Pattern}. An example for higher-order pattern unification is + + @{ML_response_fake [display, gray] + "let + val trm1 = @{term_pat \"\x y. g (?X y x) (f (?Y x))\"} + val trm2 = @{term_pat \"\u v. g u (f u)\"} + val init = Envir.empty 0 + val env = Pattern.unify @{theory} (trm1, trm2) init +in + pretty_env @{context} (Envir.term_env env) +end" + "[?X := \y x. x, ?Y := \x. x]"} + + The function @{ML_ind "Envir.empty"} generates a record with a specified + max-index for the schematic variables (in the example the index is @{text + 0}) and empty type and term environments. The function @{ML_ind + "Envir.term_env"} pulls out the term environment from the result record. The + function for type environment is @{ML_ind "Envir.type_env"}. An assumption of + this function is that the terms to be unified have already the same type. In + case of failure, the exceptions that are raised are either @{text Pattern}, + @{text MATCH} or @{text Unif}. + + As mentioned before, unrestricted higher-order unification, respectively + higher-order matching, is in general undecidable and might also not posses a + single most general solution. Therefore Isabelle implements the unification + function @{ML_ind unifiers in Unify} so that it returns a lazy list of + potentially infinite unifiers. An example is as follows +*} + +ML{*val uni_seq = +let + val trm1 = @{term_pat "?X ?Y"} + val trm2 = @{term "f a"} + val init = Envir.empty 0 +in + Unify.unifiers (@{theory}, init, [(trm1, trm2)]) +end *} + +text {* + The unifiers can be extracted from the lazy sequence using the + function @{ML_ind "Seq.pull"}. In the example we obtain three + unifiers @{text "un1\un3"}. +*} + +ML{*val SOME ((un1, _), next1) = Seq.pull uni_seq; +val SOME ((un2, _), next2) = Seq.pull next1; +val SOME ((un3, _), next3) = Seq.pull next2; +val NONE = Seq.pull next3 *} + +text {* + \footnote{\bf FIXME: what is the list of term pairs in the unifier: flex-flex pairs?} + + We can print them out as follows. + + @{ML_response_fake [display, gray] + "pretty_env @{context} (Envir.term_env un1); +pretty_env @{context} (Envir.term_env un2); +pretty_env @{context} (Envir.term_env un3)" + "[?X := \a. a, ?Y := f a] +[?X := f, ?Y := a] +[?X := \b. f a]"} + + + In case of failure the function @{ML_ind unifiers in Unify} does not raise + an exception, rather returns the empty sequence. For example + + @{ML_response [display, gray] +"let + val trm1 = @{term \"a\"} + val trm2 = @{term \"b\"} + val init = Envir.empty 0 +in + Unify.unifiers (@{theory}, init, [(trm1, trm2)]) + |> Seq.pull +end" +"NONE"} + + In order to find a + reasonable solution for a unification problem, Isabelle also tries first to + solve the problem by higher-order pattern unification. + + For higher-order + matching the function is called @{ML_ind matchers in Unify} implemented + in the structure @{ML_struct Unify}. Also this + function returns sequences with possibly more than one matcher. + Like @{ML unifiers in Unify}, this function does not raise an exception + in case of failure, but returns an empty sequence. It also first tries + out whether the matching problem can be solved by first-order matching. + + \begin{readmore} + Unification and matching of higher-order patterns is implemented in + @{ML_file "Pure/pattern.ML"}. This file also contains a first-order matcher + for terms. Full higher-order unification is implemented + in @{ML_file "Pure/unify.ML"}. It uses lazy sequences which are implemented + in @{ML_file "Pure/General/seq.ML"}. + \end{readmore} +*} + +section {* Sorts (TBD) *} + + +section {* Type-Checking\label{sec:typechecking} *} + +text {* + Remember Isabelle follows the Church-style typing for terms, i.e., a term contains + enough typing information (constants, free variables and abstractions all have typing + information) so that it is always clear what the type of a term is. + Given a well-typed term, the function @{ML_ind type_of in Term} returns the + type of a term. Consider for example: + + @{ML_response [display,gray] + "type_of (@{term \"f::nat \ bool\"} $ @{term \"x::nat\"})" "bool"} + + To calculate the type, this function traverses the whole term and will + detect any typing inconsistency. For example changing the type of the variable + @{term "x"} from @{typ "nat"} to @{typ "int"} will result in the error message: + + @{ML_response_fake [display,gray] + "type_of (@{term \"f::nat \ bool\"} $ @{term \"x::int\"})" + "*** Exception- TYPE (\"type_of: type mismatch in application\" \"} + + Since the complete traversal might sometimes be too costly and + not necessary, there is the function @{ML_ind fastype_of in Term}, which + also returns the type of a term. + + @{ML_response [display,gray] + "fastype_of (@{term \"f::nat \ bool\"} $ @{term \"x::nat\"})" "bool"} + + However, efficiency is gained on the expense of skipping some tests. You + can see this in the following example + + @{ML_response [display,gray] + "fastype_of (@{term \"f::nat \ bool\"} $ @{term \"x::int\"})" "bool"} + + where no error is detected. + + Sometimes it is a bit inconvenient to construct a term with + complete typing annotations, especially in cases where the typing + information is redundant. A short-cut is to use the ``place-holder'' + type @{ML_ind dummyT in Term} and then let type-inference figure out the + complete type. An example is as follows: + + @{ML_response_fake [display,gray] +"let + val c = Const (@{const_name \"plus\"}, dummyT) + val o = @{term \"1::nat\"} + val v = Free (\"x\", dummyT) +in + Syntax.check_term @{context} (c $ o $ v) +end" +"Const (\"HOL.plus_class.plus\", \"nat \ nat \ nat\") $ + Const (\"HOL.one_class.one\", \"nat\") $ Free (\"x\", \"nat\")"} + + Instead of giving explicitly the type for the constant @{text "plus"} and the free + variable @{text "x"}, type-inference fills in the missing information. + + \begin{readmore} + See @{ML_file "Pure/Syntax/syntax.ML"} where more functions about reading, + checking and pretty-printing of terms are defined. Functions related to + type-inference are implemented in @{ML_file "Pure/type.ML"} and + @{ML_file "Pure/type_infer.ML"}. + \end{readmore} + + \footnote{\bf FIXME: say something about sorts.} + \footnote{\bf FIXME: give a ``readmore''.} + + \begin{exercise} + Check that the function defined in Exercise~\ref{fun:revsum} returns a + result that type-checks. See what happens to the solutions of this + exercise given in Appendix \ref{ch:solutions} when they receive an + ill-typed term as input. + \end{exercise} +*} + +section {* Certified Terms and Certified Types *} + +text {* + You can freely construct and manipulate @{ML_type "term"}s and @{ML_type + typ}es, since they are just arbitrary unchecked trees. However, you + eventually want to see if a term is well-formed, or type-checks, relative to + a theory. Type-checking is done via the function @{ML_ind cterm_of in Thm}, which + converts a @{ML_type term} into a @{ML_type cterm}, a \emph{certified} + term. Unlike @{ML_type term}s, which are just trees, @{ML_type "cterm"}s are + abstract objects that are guaranteed to be type-correct, and they can only + be constructed via ``official interfaces''. + + Certification is always relative to a theory context. For example you can + write: + + @{ML_response_fake [display,gray] + "cterm_of @{theory} @{term \"(a::nat) + b = c\"}" + "a + b = c"} + + This can also be written with an antiquotation: + + @{ML_response_fake [display,gray] + "@{cterm \"(a::nat) + b = c\"}" + "a + b = c"} + + Attempting to obtain the certified term for + + @{ML_response_fake_both [display,gray] + "@{cterm \"1 + True\"}" + "Type unification failed \"} + + yields an error (since the term is not typable). A slightly more elaborate + example that type-checks is: + +@{ML_response_fake [display,gray] +"let + val natT = @{typ \"nat\"} + val zero = @{term \"0::nat\"} + val plus = Const (@{const_name plus}, [natT, natT] ---> natT) +in + cterm_of @{theory} (plus $ zero $ zero) +end" + "0 + 0"} + + In Isabelle not just terms need to be certified, but also types. For example, + you obtain the certified type for the Isabelle type @{typ "nat \ bool"} on + the ML-level as follows: + + @{ML_response_fake [display,gray] + "ctyp_of @{theory} (@{typ nat} --> @{typ bool})" + "nat \ bool"} + + or with the antiquotation: + + @{ML_response_fake [display,gray] + "@{ctyp \"nat \ bool\"}" + "nat \ bool"} + + Since certified terms are, unlike terms, abstract objects, we cannot + pattern-match against them. However, we can construct them. For example + the function @{ML_ind capply in Thm} produces a certified application. + + @{ML_response_fake [display,gray] + "Thm.capply @{cterm \"P::nat \ bool\"} @{cterm \"3::nat\"}" + "P 3"} + + Similarly the function @{ML_ind list_comb in Drule} from the structure @{ML_struct Drule} + applies a list of @{ML_type cterm}s. + + @{ML_response_fake [display,gray] + "let + val chead = @{cterm \"P::unit \ nat \ bool\"} + val cargs = [@{cterm \"()\"}, @{cterm \"3::nat\"}] +in + Drule.list_comb (chead, cargs) +end" + "P () 3"} + + \begin{readmore} + For functions related to @{ML_type cterm}s and @{ML_type ctyp}s see + the files @{ML_file "Pure/thm.ML"}, @{ML_file "Pure/more_thm.ML"} and + @{ML_file "Pure/drule.ML"}. + \end{readmore} +*} + +section {* Theorems *} + +text {* + Just like @{ML_type cterm}s, theorems are abstract objects of type @{ML_type thm} + that can only be built by going through interfaces. As a consequence, every proof + in Isabelle is correct by construction. This follows the tradition of the LCF-approach. + + + To see theorems in ``action'', let us give a proof on the ML-level for the following + statement: +*} + + lemma + assumes assm\<^isub>1: "\(x::nat). P x \ Q x" + and assm\<^isub>2: "P t" + shows "Q t"(*<*)oops(*>*) + +text {* + The corresponding ML-code is as follows: +*} + +ML{*val my_thm = +let + val assm1 = @{cprop "\(x::nat). P x \ Q x"} + val assm2 = @{cprop "(P::nat \ bool) t"} + + val Pt_implies_Qt = + assume assm1 + |> forall_elim @{cterm "t::nat"} + + val Qt = implies_elim Pt_implies_Qt (assume assm2) +in + Qt + |> implies_intr assm2 + |> implies_intr assm1 +end*} + +text {* + If we print out the value of @{ML my_thm} then we see only the + final statement of the theorem. + + @{ML_response_fake [display, gray] + "tracing (string_of_thm @{context} my_thm)" + "\\x. P x \ Q x; P t\ \ Q t"} + + However, internally the code-snippet constructs the following + proof. + + \[ + \infer[(@{text "\"}$-$intro)]{\vdash @{prop "(\x. P x \ Q x) \ P t \ Q t"}} + {\infer[(@{text "\"}$-$intro)]{@{prop "\x. P x \ Q x"} \vdash @{prop "P t \ Q t"}} + {\infer[(@{text "\"}$-$elim)]{@{prop "\x. P x \ Q x"}, @{prop "P t"} \vdash @{prop "Q t"}} + {\infer[(@{text "\"}$-$elim)]{@{prop "\x. P x \ Q x"} \vdash @{prop "P t \ Q t"}} + {\infer[(assume)]{@{prop "\x. P x \ Q x"} \vdash @{prop "\x. P x \ Q x"}}{}} + & + \infer[(assume)]{@{prop "P t"} \vdash @{prop "P t"}}{} + } + } + } + \] + + While we obtained a theorem as result, this theorem is not + yet stored in Isabelle's theorem database. Consequently, it cannot be + referenced on the user level. One way to store it in the theorem database is + by using the function @{ML_ind note in Local_Theory}.\footnote{\bf FIXME: make sure a pointer + to the section about local-setup is given earlier.} +*} + +local_setup %gray {* + Local_Theory.note ((@{binding "my_thm"}, []), [my_thm]) #> snd *} + +text {* + The fourth argument of @{ML note in Local_Theory} is the list of theorems we + want to store under a name. We can store more than one under a single name. + The first argument @{ML_ind theoremK in Thm} is + a kind indicator, which classifies the theorem. There are several such kind + indicators: for a theorem arising from a definition you should use @{ML_ind + definitionK in Thm}, and for + ``normal'' theorems the kinds @{ML_ind theoremK in Thm} or @{ML_ind lemmaK + in Thm}. The second argument of @{ML note in Local_Theory} is the name under + which we store the theorem or theorems. The third argument can contain a + list of theorem attributes, which we will explain in detail in + Section~\ref{sec:attributes}. Below we just use one such attribute for + adding the theorem to the simpset: +*} + +local_setup %gray {* + Local_Theory.note ((@{binding "my_thm_simp"}, + [Attrib.internal (K Simplifier.simp_add)]), [my_thm]) #> snd *} + +text {* + Note that we have to use another name under which the theorem is stored, + since Isabelle does not allow us to call @{ML_ind note in Local_Theory} twice + with the same name. The attribute needs to be wrapped inside the function @{ML_ind + internal in Attrib} from the structure @{ML_struct Attrib}. If we use the function + @{ML get_thm_names_from_ss} from + the previous chapter, we can check whether the theorem has actually been + added. + + + @{ML_response [display,gray] + "let + fun pred s = match_string \"my_thm_simp\" s +in + exists pred (get_thm_names_from_ss @{simpset}) +end" + "true"} + + The main point of storing the theorems @{thm [source] my_thm} and @{thm + [source] my_thm_simp} is that they can now also be referenced with the + \isacommand{thm}-command on the user-level of Isabelle + + + \begin{isabelle} + \isacommand{thm}~@{text "my_thm"}\isanewline + @{text ">"}~@{prop "\\x. P x \ Q x; P t\ \ Q t"} + \end{isabelle} + + or with the @{text "@{thm \}"}-antiquotation on the ML-level. Otherwise the + user has no access to these theorems. + + Recall that Isabelle does not let you call @{ML note in Local_Theory} twice + with the same theorem name. In effect, once a theorem is stored under a name, + this association is fixed. While this is a ``safety-net'' to make sure a + theorem name refers to a particular theorem or collection of theorems, it is + also a bit too restrictive in cases where a theorem name should refer to a + dynamically expanding list of theorems (like a simpset). Therefore Isabelle + also implements a mechanism where a theorem name can refer to a custom theorem + list. For this you can use the function @{ML_ind add_thms_dynamic in PureThy}. + To see how it works let us assume we defined our own theorem list @{text MyThmList}. +*} + +ML{*structure MyThmList = Generic_Data + (type T = thm list + val empty = [] + val extend = I + val merge = merge Thm.eq_thm_prop) + +fun update thm = Context.theory_map (MyThmList.map (Thm.add_thm thm))*} + +text {* + \footnote{\bf explain @{ML_ind add_thm in Thm} and @{ML_ind eq_thm_prop in Thm}.} + + The function @{ML update} allows us to update the theorem list, for example + by adding the theorem @{thm [source] TrueI}. +*} + +setup %gray {* update @{thm TrueI} *} + +text {* + We can now install the theorem list so that it is visible to the user and + can be refered to by a theorem name. For this need to call + @{ML_ind add_thms_dynamic in PureThy} +*} + +setup %gray {* + PureThy.add_thms_dynamic (@{binding "mythmlist"}, MyThmList.get) +*} + +text {* + with a name and a function that accesses the theorem list. Now if the + user issues the command + + \begin{isabelle} + \isacommand{thm}~@{text "mythmlist"}\\ + @{text "> True"} + \end{isabelle} + + the current content of the theorem list is displayed. If more theorems are stored in + the list, say +*} + +setup %gray {* update @{thm FalseE} *} + +text {* + then the same command produces + + \begin{isabelle} + \isacommand{thm}~@{text "mythmlist"}\\ + @{text "> False \ ?P"}\\ + @{text "> True"} + \end{isabelle} + + There is a multitude of functions in the structures @{ML_struct Thm} and @{ML_struct Drule} + for managing or manipulating theorems. For example + we can test theorems for alpha equality. Suppose you proved the following three + theorems. +*} + +lemma + shows thm1: "\x. P x" + and thm2: "\y. P y" + and thm3: "\y. Q y" sorry + +text {* + Testing them for alpha equality using the function @{ML_ind eq_thm in Thm} produces: + + @{ML_response [display,gray] +"(Thm.eq_thm (@{thm thm1}, @{thm thm2}), + Thm.eq_thm (@{thm thm2}, @{thm thm3}))" +"(true, false)"} + + Many functions destruct theorems into @{ML_type cterm}s. For example + the functions @{ML_ind lhs_of in Thm} and @{ML_ind rhs_of in Thm} return + the left and right-hand side, respectively, of a meta-equality. + + @{ML_response_fake [display,gray] + "let + val eq = @{thm True_def} +in + (Thm.lhs_of eq, Thm.rhs_of eq) + |> pairself (string_of_cterm @{context}) +end" + "(True, (\x. x) = (\x. x))"} + + Other function produce terms that can be pattern-matched. + Suppose the following two theorems. +*} + +lemma + shows foo_test1: "A \ B \ C" + and foo_test2: "A \ B \ C" sorry + +text {* + We can destruct them into premises and conclusions as follows. + + @{ML_response_fake [display,gray] +"let + val ctxt = @{context} + fun prems_and_concl thm = + [\"Premises: \" ^ (string_of_terms ctxt (Thm.prems_of thm))] @ + [\"Conclusion: \" ^ (string_of_term ctxt (Thm.concl_of thm))] + |> cat_lines + |> tracing +in + prems_and_concl @{thm foo_test1}; + prems_and_concl @{thm foo_test2} +end" +"Premises: ?A, ?B +Conclusion: ?C +Premises: +Conclusion: ?A \ ?B \ ?C"} + + Note that in the second case, there is no premise. + + \begin{readmore} + The basic functions for theorems are defined in + @{ML_file "Pure/thm.ML"}, @{ML_file "Pure/more_thm.ML"} and @{ML_file "Pure/drule.ML"}. + \end{readmore} + + Although we will explain the simplifier in more detail as tactic in + Section~\ref{sec:simplifier}, the simplifier + can be used to work directly over theorems, for example to unfold definitions. To show + this, we build the theorem @{term "True \ True"} (Line 1) and then + unfold the constant @{term "True"} according to its definition (Line 2). + + @{ML_response_fake [display,gray,linenos] + "Thm.reflexive @{cterm \"True\"} + |> Simplifier.rewrite_rule [@{thm True_def}] + |> string_of_thm @{context} + |> tracing" + "(\x. x) = (\x. x) \ (\x. x) = (\x. x)"} + + Often it is necessary to transform theorems to and from the object + logic, that is replacing all @{text "\"} and @{text "\"} by @{text "\"} + and @{text "\"}, or the other way around. A reason for such a transformation + might be stating a definition. The reason is that definitions can only be + stated using object logic connectives, while theorems using the connectives + from the meta logic are more convenient for reasoning. Therefore there are + some build in functions which help with these transformations. The function + @{ML_ind rulify in ObjectLogic} + replaces all object connectives by equivalents in the meta logic. For example + + @{ML_response_fake [display, gray] + "ObjectLogic.rulify @{thm foo_test2}" + "\?A; ?B\ \ ?C"} + + The transformation in the other direction can be achieved with function + @{ML_ind atomize in ObjectLogic} and the following code. + + @{ML_response_fake [display,gray] + "let + val thm = @{thm foo_test1} + val meta_eq = ObjectLogic.atomize (cprop_of thm) +in + MetaSimplifier.rewrite_rule [meta_eq] thm +end" + "?A \ ?B \ ?C"} + + In this code the function @{ML atomize in ObjectLogic} produces + a meta-equation between the given theorem and the theorem transformed + into the object logic. The result is the theorem with object logic + connectives. However, in order to completely transform a theorem + involving meta variables, such as @{thm [source] list.induct}, which + is of the form + + @{thm [display] list.induct} + + we have to first abstract over the meta variables @{text "?P"} and + @{text "?list"}. For this we can use the function + @{ML_ind forall_intr_vars in Drule}. This allows us to implement the + following function for atomizing a theorem. +*} + +ML{*fun atomize_thm thm = +let + val thm' = forall_intr_vars thm + val thm'' = ObjectLogic.atomize (cprop_of thm') +in + MetaSimplifier.rewrite_rule [thm''] thm' +end*} + +text {* + This function produces for the theorem @{thm [source] list.induct} + + @{ML_response_fake [display, gray] + "atomize_thm @{thm list.induct}" + "\P list. P [] \ (\a list. P list \ P (a # list)) \ P list"} + + \footnote{\bf FIXME: say someting about @{ML_ind standard in Drule}.} + + Theorems can also be produced from terms by giving an explicit proof. + One way to achieve this is by using the function @{ML_ind prove in Goal} + in the structure @{ML_struct Goal}. For example below we use this function + to prove the term @{term "P \ P"}. + + @{ML_response_fake [display,gray] + "let + val trm = @{term \"P \ P::bool\"} + val tac = K (atac 1) +in + Goal.prove @{context} [\"P\"] [] trm tac +end" + "?P \ ?P"} + + This function takes first a context and second a list of strings. This list + specifies which variables should be turned into schematic variables once the term + is proved. The fourth argument is the term to be proved. The fifth is a + corresponding proof given in form of a tactic (we explain tactics in + Chapter~\ref{chp:tactical}). In the code above, the tactic proves the theorem + by assumption. As before this code will produce a theorem, but the theorem + is not yet stored in the theorem database. + + While the LCF-approach of going through interfaces ensures soundness in Isabelle, there + is the function @{ML_ind make_thm in Skip_Proof} in the structure + @{ML_struct Skip_Proof} that allows us to turn any proposition into a theorem. + Potentially making the system unsound. This is sometimes useful for developing + purposes, or when explicit proof construction should be omitted due to performace + reasons. An example of this function is as follows: + + @{ML_response_fake [display, gray] + "Skip_Proof.make_thm @{theory} @{prop \"True = False\"}" + "True = False"} + + The function @{ML make_thm in Skip_Proof} however only works if + the ``quick-and-dirty'' mode is switched on. + + Theorems also contain auxiliary data, such as the name of the theorem, its + kind, the names for cases and so on. This data is stored in a string-string + list and can be retrieved with the function @{ML_ind get_tags in + Thm}. Assume you prove the following lemma. +*} + +lemma foo_data: + shows "P \ P \ P" by assumption + +text {* + The auxiliary data of this lemma can be retrieved using the function + @{ML_ind get_tags in Thm}. So far the the auxiliary data of this lemma is + + @{ML_response_fake [display,gray] + "Thm.get_tags @{thm foo_data}" + "[(\"name\", \"General.foo_data\"), (\"kind\", \"lemma\")]"} + + consisting of a name and a kind. When we store lemmas in the theorem database, + we might want to explicitly extend this data by attaching case names to the + two premises of the lemma. This can be done with the function @{ML_ind name in Rule_Cases} + from the structure @{ML_struct Rule_Cases}. +*} + +local_setup %gray {* + Local_Theory.note ((@{binding "foo_data'"}, []), + [(Rule_Cases.name ["foo_case_one", "foo_case_two"] + @{thm foo_data})]) #> snd *} + +text {* + The data of the theorem @{thm [source] foo_data'} is then as follows: + + @{ML_response_fake [display,gray] + "Thm.get_tags @{thm foo_data'}" + "[(\"name\", \"General.foo_data'\"), (\"kind\", \"lemma\"), + (\"case_names\", \"foo_case_one;foo_case_two\")]"} + + You can observe the case names of this lemma on the user level when using + the proof methods @{text cases} and @{text induct}. In the proof below +*} + +lemma + shows "Q \ Q \ Q" +proof (cases rule: foo_data') + +(*<*)oops(*>*) +text_raw{* +\begin{tabular}{@ {}l} +\isacommand{print\_cases}\\ +@{text "> cases:"}\\ +@{text "> foo_case_one:"}\\ +@{text "> let \"?case\" = \"?P\""}\\ +@{text "> foo_case_two:"}\\ +@{text "> let \"?case\" = \"?P\""} +\end{tabular}*} + +text {* + we can proceed by analysing the cases @{text "foo_case_one"} and + @{text "foo_case_two"}. While if the theorem has no names, then + the cases have standard names @{text 1}, @{text 2} and so + on. This can be seen in the proof below. +*} + +lemma + shows "Q \ Q \ Q" +proof (cases rule: foo_data) + +(*<*)oops(*>*) +text_raw{* +\begin{tabular}{@ {}l} +\isacommand{print\_cases}\\ +@{text "> cases:"}\\ +@{text "> 1:"}\\ +@{text "> let \"?case\" = \"?P\""}\\ +@{text "> 2:"}\\ +@{text "> let \"?case\" = \"?P\""} +\end{tabular}*} + + +text {* + One great feature of Isabelle is its document preparation system, where + proved theorems can be quoted in documents referencing directly their + formalisation. This helps tremendously to minimise cut-and-paste errors. However, + sometimes the verbatim quoting is not what is wanted or what can be shown to + readers. For such situations Isabelle allows the installation of \emph{\index*{theorem + styles}}. These are, roughly speaking, functions from terms to terms. The input + term stands for the theorem to be presented; the output can be constructed to + ones wishes. Let us, for example, assume we want to quote theorems without + leading @{text \}-quantifiers. For this we can implement the following function + that strips off @{text "\"}s. +*} + +ML %linenosgray{*fun strip_allq (Const (@{const_name "All"}, _) $ Abs body) = + Term.dest_abs body |> snd |> strip_allq + | strip_allq (Const (@{const_name "Trueprop"}, _) $ t) = + strip_allq t + | strip_allq t = t*} + +text {* + We use in Line 2 the function @{ML_ind dest_abs in Term} for deconstructing abstractions, + since this function deals correctly with potential name clashes. This function produces + a pair consisting of the variable and the body of the abstraction. We are only interested + in the body, which we feed into the recursive call. In Line 3 and 4, we also + have to explicitly strip of the outermost @{term Trueprop}-coercion. Now we can + install this function as the theorem style named @{text "my_strip_allq"}. +*} + +setup %gray {* + Term_Style.setup "my_strip_allq" (Scan.succeed (K strip_allq)) +*} + +text {* + We can test this theorem style with the following theorem +*} + +theorem style_test: + shows "\x y z. (x, x) = (y, z)" sorry + +text {* + Now printing out in a document the theorem @{thm [source] style_test} normally + using @{text "@{thm \}"} produces + + \begin{isabelle} + @{text "@{thm style_test}"}\\ + @{text ">"}~@{thm style_test} + \end{isabelle} + + as expected. But with the theorem style @{text "@{thm (my_strip_allq) \}"} + we obtain + + \begin{isabelle} + @{text "@{thm (my_strip_allq) style_test}"}\\ + @{text ">"}~@{thm (my_strip_allq) style_test}\\ + \end{isabelle} + + without the leading quantifiers. We can improve this theorem style by explicitly + giving a list of strings that should be used for the replacement of the + variables. For this we implement the function which takes a list of strings + and uses them as name in the outermost abstractions. +*} + +ML{*fun rename_allq [] t = t + | rename_allq (x::xs) (Const (@{const_name "All"}, U) $ Abs (_, T, t)) = + Const (@{const_name "All"}, U) $ Abs (x, T, rename_allq xs t) + | rename_allq xs (Const (@{const_name "Trueprop"}, U) $ t) = + rename_allq xs t + | rename_allq _ t = t*} + +text {* + We can now install a the modified theorem style as follows +*} + +setup %gray {* let + val parser = Scan.repeat Args.name + fun action xs = K (rename_allq xs #> strip_allq) +in + Term_Style.setup "my_strip_allq2" (parser >> action) +end *} + +text {* + The parser reads a list of names. In the function @{text action} we first + call @{ML rename_allq} with the parsed list, then we call @{ML strip_allq} + on the resulting term. We can now suggest, for example, two variables for + stripping off the first two @{text \}-quantifiers. + + + \begin{isabelle} + @{text "@{thm (my_strip_allq2 x' x'') style_test}"}\\ + @{text ">"}~@{thm (my_strip_allq2 x' x'') style_test} + \end{isabelle} + + Such theorem styles allow one to print out theorems in documents formatted to + ones heart content. Next we explain theorem attributes, which is another + mechanism for dealing with theorems. + + \begin{readmore} + Theorem styles are implemented in @{ML_file "Pure/Thy/term_style.ML"}. + \end{readmore} +*} + +section {* Theorem Attributes\label{sec:attributes} *} + +text {* + Theorem attributes are @{text "[symmetric]"}, @{text "[THEN \]"}, @{text + "[simp]"} and so on. Such attributes are \emph{neither} tags \emph{nor} flags + annotated to theorems, but functions that do further processing of + theorems. In particular, it is not possible to find out + what are all theorems that have a given attribute in common, unless of course + the function behind the attribute stores the theorems in a retrievable + data structure. + + If you want to print out all currently known attributes a theorem can have, + you can use the Isabelle command + + \begin{isabelle} + \isacommand{print\_attributes}\\ + @{text "> COMP: direct composition with rules (no lifting)"}\\ + @{text "> HOL.dest: declaration of Classical destruction rule"}\\ + @{text "> HOL.elim: declaration of Classical elimination rule"}\\ + @{text "> \"} + \end{isabelle} + + The theorem attributes fall roughly into two categories: the first category manipulates + theorems (for example @{text "[symmetric]"} and @{text "[THEN \]"}), and the second + stores theorems somewhere as data (for example @{text "[simp]"}, which adds + theorems to the current simpset). + + To explain how to write your own attribute, let us start with an extremely simple + version of the attribute @{text "[symmetric]"}. The purpose of this attribute is + to produce the ``symmetric'' version of an equation. The main function behind + this attribute is +*} + +ML{*val my_symmetric = Thm.rule_attribute (fn _ => fn thm => thm RS @{thm sym})*} + +text {* + where the function @{ML_ind rule_attribute in Thm} expects a function taking a + context (which we ignore in the code above) and a theorem (@{text thm}), and + returns another theorem (namely @{text thm} resolved with the theorem + @{thm [source] sym}: @{thm sym[no_vars]}; the function @{ML_ind RS in Drule} + is explained in Section~\ref{sec:simpletacs}). The function + @{ML rule_attribute in Thm} then returns an attribute. + + Before we can use the attribute, we need to set it up. This can be done + using the Isabelle command \isacommand{attribute\_setup} as follows: +*} + +attribute_setup %gray my_sym = + {* Scan.succeed my_symmetric *} "applying the sym rule" + +text {* + Inside the @{text "\ \ \"}, we have to specify a parser + for the theorem attribute. Since the attribute does not expect any further + arguments (unlike @{text "[THEN \]"}, for instance), we use the parser @{ML + Scan.succeed}. An example for the attribute @{text "[my_sym]"} is the proof +*} + +lemma test[my_sym]: "2 = Suc (Suc 0)" by simp + +text {* + which stores the theorem @{thm test} under the name @{thm [source] test}. You + can see this, if you query the lemma: + + \begin{isabelle} + \isacommand{thm}~@{text "test"}\\ + @{text "> "}~@{thm test} + \end{isabelle} + + We can also use the attribute when referring to this theorem: + + \begin{isabelle} + \isacommand{thm}~@{text "test[my_sym]"}\\ + @{text "> "}~@{thm test[my_sym]} + \end{isabelle} + + An alternative for setting up an attribute is the function @{ML_ind setup in Attrib}. + So instead of using \isacommand{attribute\_setup}, you can also set up the + attribute as follows: +*} + +ML{*Attrib.setup @{binding "my_sym"} (Scan.succeed my_symmetric) + "applying the sym rule" *} + +text {* + This gives a function from @{ML_type "theory -> theory"}, which + can be used for example with \isacommand{setup} or with + @{ML "Context.>> o Context.map_theory"}.\footnote{\bf FIXME: explain what happens here.} + + As an example of a slightly more complicated theorem attribute, we implement + our own version of @{text "[THEN \]"}. This attribute will take a list of theorems + as argument and resolve the theorem with this list (one theorem + after another). The code for this attribute is +*} + +ML{*fun MY_THEN thms = + Thm.rule_attribute + (fn _ => fn thm => fold (curry ((op RS) o swap)) thms thm)*} + +text {* + where @{ML swap} swaps the components of a pair. The setup of this theorem + attribute uses the parser @{ML thms in Attrib}, which parses a list of + theorems. +*} + +attribute_setup %gray MY_THEN = {* Attrib.thms >> MY_THEN *} + "resolving the list of theorems with the theorem" + +text {* + You can, for example, use this theorem attribute to turn an equation into a + meta-equation: + + \begin{isabelle} + \isacommand{thm}~@{text "test[MY_THEN eq_reflection]"}\\ + @{text "> "}~@{thm test[MY_THEN eq_reflection]} + \end{isabelle} + + If you need the symmetric version as a meta-equation, you can write + + \begin{isabelle} + \isacommand{thm}~@{text "test[MY_THEN sym eq_reflection]"}\\ + @{text "> "}~@{thm test[MY_THEN sym eq_reflection]} + \end{isabelle} + + It is also possible to combine different theorem attributes, as in: + + \begin{isabelle} + \isacommand{thm}~@{text "test[my_sym, MY_THEN eq_reflection]"}\\ + @{text "> "}~@{thm test[my_sym, MY_THEN eq_reflection]} + \end{isabelle} + + However, here also a weakness of the concept + of theorem attributes shows through: since theorem attributes can be + arbitrary functions, they do not commute in general. If you try + + \begin{isabelle} + \isacommand{thm}~@{text "test[MY_THEN eq_reflection, my_sym]"}\\ + @{text "> "}~@{text "exception THM 1 raised: RSN: no unifiers"} + \end{isabelle} + + you get an exception indicating that the theorem @{thm [source] sym} + does not resolve with meta-equations. + + The purpose of @{ML_ind rule_attribute in Thm} is to directly manipulate + theorems. Another usage of theorem attributes is to add and delete theorems + from stored data. For example the theorem attribute @{text "[simp]"} adds + or deletes a theorem from the current simpset. For these applications, you + can use @{ML_ind declaration_attribute in Thm}. To illustrate this function, + let us introduce a theorem list. +*} + +ML{*structure MyThms = Named_Thms + (val name = "attr_thms" + val description = "Theorems for an Attribute") *} + +text {* + We are going to modify this list by adding and deleting theorems. + For this we use the two functions @{ML MyThms.add_thm} and + @{ML MyThms.del_thm}. You can turn them into attributes + with the code +*} + +ML{*val my_add = Thm.declaration_attribute MyThms.add_thm +val my_del = Thm.declaration_attribute MyThms.del_thm *} + +text {* + and set up the attributes as follows +*} + +attribute_setup %gray my_thms = {* Attrib.add_del my_add my_del *} + "maintaining a list of my_thms" + +text {* + The parser @{ML_ind add_del in Attrib} is a predefined parser for + adding and deleting lemmas. Now if you prove the next lemma + and attach to it the attribute @{text "[my_thms]"} +*} + +lemma trueI_2[my_thms]: "True" by simp + +text {* + then you can see it is added to the initially empty list. + + @{ML_response_fake [display,gray] + "MyThms.get @{context}" + "[\"True\"]"} + + You can also add theorems using the command \isacommand{declare}. +*} + +declare test[my_thms] trueI_2[my_thms add] + +text {* + With this attribute, the @{text "add"} operation is the default and does + not need to be explicitly given. These three declarations will cause the + theorem list to be updated as: + + @{ML_response_fake [display,gray] + "MyThms.get @{context}" + "[\"True\", \"Suc (Suc 0) = 2\"]"} + + The theorem @{thm [source] trueI_2} only appears once, since the + function @{ML_ind add_thm in Thm} tests for duplicates, before extending + the list. Deletion from the list works as follows: +*} + +declare test[my_thms del] + +text {* After this, the theorem list is again: + + @{ML_response_fake [display,gray] + "MyThms.get @{context}" + "[\"True\"]"} + + We used in this example two functions declared as @{ML_ind + declaration_attribute in Thm}, but there can be any number of them. We just + have to change the parser for reading the arguments accordingly. + + \footnote{\bf FIXME What are: @{text "theory_attributes"}, @{text "proof_attributes"}?} + + \begin{readmore} + FIXME: @{ML_file "Pure/more_thm.ML"}; parsers for attributes is in + @{ML_file "Pure/Isar/attrib.ML"}...also explained in the chapter about + parsing. + \end{readmore} +*} + +section {* Pretty-Printing\label{sec:pretty} *} + +text {* + So far we printed out only plain strings without any formatting except for + occasional explicit line breaks using @{text [quotes] "\\n"}. This is + sufficient for ``quick-and-dirty'' printouts. For something more + sophisticated, Isabelle includes an infrastructure for properly formatting + text. Most of its functions do not operate on @{ML_type string}s, but on + instances of the pretty type: + + @{ML_type_ind [display, gray] "Pretty.T"} + + The function @{ML str in Pretty} transforms a (plain) string into such a pretty + type. For example + + @{ML_response_fake [display,gray] + "Pretty.str \"test\"" "String (\"test\", 4)"} + + where the result indicates that we transformed a string with length 4. Once + you have a pretty type, you can, for example, control where linebreaks may + occur in case the text wraps over a line, or with how much indentation a + text should be printed. However, if you want to actually output the + formatted text, you have to transform the pretty type back into a @{ML_type + string}. This can be done with the function @{ML_ind string_of in Pretty}. In what + follows we will use the following wrapper function for printing a pretty + type: +*} + +ML{*fun pprint prt = tracing (Pretty.string_of prt)*} + +text {* + The point of the pretty-printing infrastructure is to give hints about how to + layout text and let Isabelle do the actual layout. Let us first explain + how you can insert places where a line break can occur. For this assume the + following function that replicates a string n times: +*} + +ML{*fun rep n str = implode (replicate n str) *} + +text {* + and suppose we want to print out the string: +*} + +ML{*val test_str = rep 8 "fooooooooooooooobaaaaaaaaaaaar "*} + +text {* + We deliberately chose a large string so that it spans over more than one line. + If we print out the string using the usual ``quick-and-dirty'' method, then + we obtain the ugly output: + +@{ML_response_fake [display,gray] +"tracing test_str" +"fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar foooooooooo +ooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaa +aaaaaaar fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar fo +oooooooooooooobaaaaaaaaaaaar"} + + We obtain the same if we just use the function @{ML pprint}. + +@{ML_response_fake [display,gray] +"pprint (Pretty.str test_str)" +"fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar foooooooooo +ooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaa +aaaaaaar fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar fo +oooooooooooooobaaaaaaaaaaaar"} + + However by using pretty types you have the ability to indicate possible + linebreaks for example at each whitespace. You can achieve this with the + function @{ML_ind breaks in Pretty}, which expects a list of pretty types + and inserts a possible line break in between every two elements in this + list. To print this list of pretty types as a single string, we concatenate + them with the function @{ML_ind blk in Pretty} as follows: + +@{ML_response_fake [display,gray] +"let + val ptrs = map Pretty.str (space_explode \" \" test_str) +in + pprint (Pretty.blk (0, Pretty.breaks ptrs)) +end" +"fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar +fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar +fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar +fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar"} + + Here the layout of @{ML test_str} is much more pleasing to the + eye. The @{ML "0"} in @{ML_ind blk in Pretty} stands for no hanging + indentation of the printed string. You can increase the indentation + and obtain + +@{ML_response_fake [display,gray] +"let + val ptrs = map Pretty.str (space_explode \" \" test_str) +in + pprint (Pretty.blk (3, Pretty.breaks ptrs)) +end" +"fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar + fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar + fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar + fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar"} + + where starting from the second line the indent is 3. If you want + that every line starts with the same indent, you can use the + function @{ML_ind indent in Pretty} as follows: + +@{ML_response_fake [display,gray] +"let + val ptrs = map Pretty.str (space_explode \" \" test_str) +in + pprint (Pretty.indent 10 (Pretty.blk (0, Pretty.breaks ptrs))) +end" +" fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar + fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar + fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar + fooooooooooooooobaaaaaaaaaaaar fooooooooooooooobaaaaaaaaaaaar"} + + If you want to print out a list of items separated by commas and + have the linebreaks handled properly, you can use the function + @{ML_ind commas in Pretty}. For example + +@{ML_response_fake [display,gray] +"let + val ptrs = map (Pretty.str o string_of_int) (99998 upto 100020) +in + pprint (Pretty.blk (0, Pretty.commas ptrs)) +end" +"99998, 99999, 100000, 100001, 100002, 100003, 100004, 100005, 100006, +100007, 100008, 100009, 100010, 100011, 100012, 100013, 100014, 100015, +100016, 100017, 100018, 100019, 100020"} + + where @{ML upto} generates a list of integers. You can print out this + list as a ``set'', that means enclosed inside @{text [quotes] "{"} and + @{text [quotes] "}"}, and separated by commas using the function + @{ML_ind enum in Pretty}. For example +*} + +text {* + +@{ML_response_fake [display,gray] +"let + val ptrs = map (Pretty.str o string_of_int) (99998 upto 100020) +in + pprint (Pretty.enum \",\" \"{\" \"}\" ptrs) +end" +"{99998, 99999, 100000, 100001, 100002, 100003, 100004, 100005, 100006, + 100007, 100008, 100009, 100010, 100011, 100012, 100013, 100014, 100015, + 100016, 100017, 100018, 100019, 100020}"} + + As can be seen, this function prints out the ``set'' so that starting + from the second, each new line has an indentation of 2. + + If you print out something that goes beyond the capabilities of the + standard functions, you can do relatively easily the formatting + yourself. Assume you want to print out a list of items where like in ``English'' + the last two items are separated by @{text [quotes] "and"}. For this you can + write the function + +*} + +ML %linenosgray{*fun and_list [] = [] + | and_list [x] = [x] + | and_list xs = + let + val (front, last) = split_last xs + in + (Pretty.commas front) @ + [Pretty.brk 1, Pretty.str "and", Pretty.brk 1, last] + end *} + +text {* + where Line 7 prints the beginning of the list and Line + 8 the last item. We have to use @{ML "Pretty.brk 1"} in order + to insert a space (of length 1) before the + @{text [quotes] "and"}. This space is also a place where a line break + can occur. We do the same after the @{text [quotes] "and"}. This gives you + for example + +@{ML_response_fake [display,gray] +"let + val ptrs1 = map (Pretty.str o string_of_int) (1 upto 22) + val ptrs2 = map (Pretty.str o string_of_int) (10 upto 28) +in + pprint (Pretty.blk (0, and_list ptrs1)); + pprint (Pretty.blk (0, and_list ptrs2)) +end" +"1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 +and 22 +10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27 and +28"} + + Next we like to pretty-print a term and its type. For this we use the + function @{text "tell_type"}. +*} + +ML %linenosgray{*fun tell_type ctxt t = +let + fun pstr s = Pretty.breaks (map Pretty.str (space_explode " " s)) + val ptrm = Pretty.quote (Syntax.pretty_term ctxt t) + val pty = Pretty.quote (Syntax.pretty_typ ctxt (fastype_of t)) +in + pprint (Pretty.blk (0, + (pstr "The term " @ [ptrm] @ pstr " has type " + @ [pty, Pretty.str "."]))) +end*} + +text {* + In Line 3 we define a function that inserts possible linebreaks in places + where a space is. In Lines 4 and 5 we pretty-print the term and its type + using the functions @{ML_ind pretty_term in Syntax} and @{ML_ind + pretty_typ in Syntax}. We also use the function @{ML_ind quote in + Pretty} in order to enclose the term and type inside quotation marks. In + Line 9 we add a period right after the type without the possibility of a + line break, because we do not want that a line break occurs there. + Now you can write + + @{ML_response_fake [display,gray] + "tell_type @{context} @{term \"min (Suc 0)\"}" + "The term \"min (Suc 0)\" has type \"nat \ nat\"."} + + To see the proper line breaking, you can try out the function on a bigger term + and type. For example: + + @{ML_response_fake [display,gray] + "tell_type @{context} @{term \"op = (op = (op = (op = (op = op =))))\"}" + "The term \"op = (op = (op = (op = (op = op =))))\" has type +\"((((('a \ 'a \ bool) \ bool) \ bool) \ bool) \ bool) \ bool\"."} + + The function @{ML_ind big_list in Pretty} helps with printing long lists. + It is used for example in the command \isacommand{print\_theorems}. An + example is as follows. + + @{ML_response_fake [display,gray] + "let + val pstrs = map (Pretty.str o string_of_int) (4 upto 10) +in + pprint (Pretty.big_list \"header\" pstrs) +end" + "header + 4 + 5 + 6 + 7 + 8 + 9 + 10"} + + Like @{ML blk in Pretty}, the function @{ML_ind chunks in Pretty} prints out + a list of items, but automatically inserts forced breaks between each item. + Compare + + @{ML_response_fake [display,gray] + "let + val a_and_b = [Pretty.str \"a\", Pretty.str \"b\"] +in + pprint (Pretty.blk (0, a_and_b)); + pprint (Pretty.chunks a_and_b) +end" +"ab +a +b"} + + \footnote{\bf FIXME: What happens with printing big formulae?} + + + + \begin{readmore} + The general infrastructure for pretty-printing is implemented in the file + @{ML_file "Pure/General/pretty.ML"}. The file @{ML_file "Pure/Syntax/syntax.ML"} + contains pretty-printing functions for terms, types, theorems and so on. + + @{ML_file "Pure/General/markup.ML"} + \end{readmore} +*} + +(* +text {* + printing into the goal buffer as part of the proof state +*} + +text {* writing into the goal buffer *} + +ML {* fun my_hook interactive state = + (interactive ? Proof.goal_message (fn () => Pretty.str +"foo")) state +*} + +setup %gray {* Context.theory_map (Specification.add_theorem_hook my_hook) *} + +lemma "False" +oops +*) + +(* +ML {* +fun setmp_show_all_types f = + setmp show_all_types + (! show_types orelse ! show_sorts orelse ! show_all_types) f; + +val ctxt = @{context}; +val t1 = @{term "undefined::nat"}; +val t2 = @{term "Suc y"}; +val pty = Pretty.block (Pretty.breaks + [(setmp show_question_marks false o setmp_show_all_types) + (Syntax.pretty_term ctxt) t1, + Pretty.str "=", Syntax.pretty_term ctxt t2]); +pty |> Pretty.string_of +*} + +text {* the infrastructure of Syntax-pretty-term makes sure it is printed nicely *} + + +ML {* Pretty.mark Markup.hilite (Pretty.str "foo") |> Pretty.string_of |> tracing *} +ML {* (Pretty.str "bar") |> Pretty.string_of |> tracing *} +*) + +section {* Summary *} + +text {* + \begin{conventions} + \begin{itemize} + \item Start with a proper context and then pass it around + through all your functions. + \end{itemize} + \end{conventions} +*} + +end