theory Antiquotes

imports "../Base"

begin

section {* Useful Document Antiquotations *}

text {*

  {\bf Problem:} 

  How to keep your ML-code inside a document synchronised with the actual code?\smallskip

  {\bf Solution:} This can be achieved using document antiquotations.\smallskip

  Document antiquotations can be used for ensuring consistent type-setting of

  various entities in a document. They can also be used for sophisticated

  \LaTeX-hacking. If you type @{text "Ctrl-c Ctrl-a h A"} inside ProofGeneral, you

  obtain a list of all currently available document antiquotations and their options.

  You obtain the same list on the ML-level by typing

  @{ML [display,gray] "ThyOutput.print_antiquotations ()"}

  Below we give the code for two additional antiquotations that can be used to typeset

  ML-code and also to check whether the given code actually compiles. This

  provides a sanity check for the code and also allows one to keep documents

  in sync with other code, for example Isabelle.

  We first describe the antiquotation @{text "ML_checked"} with the syntax:

  @{text [display] "@{ML_checked \"a_piece_of_code\"}"}

  The code is checked by sending the ML-expression @{text [quotes] "val _ =

  a_piece_of_code"} to the ML-compiler (i.e.~the function @{ML

  "ML_Context.eval_in"} in Line 4 below). The complete code of the

  antiquotation is as follows:

*}

ML%linenosgray{*fun ml_val code_txt = "val _ = " ^ code_txt

  (ML_Context.eval_in (SOME ctxt) false Position.none (ml_val code_txt); 

text {*

  Note that the parser @{ML "(Scan.lift Args.name)"} in line 9 parses a string, 

  in this case the code given as argument. As mentioned before, this argument 

  is sent to the ML-compiler in the line 4 using the function @{ML ml_val},

  which constructs the appropriate ML-expression.

  If the code is ``approved'' by the compiler, then the output function @{ML

  code. This function expects that the code is a list of strings where each

  string correspond to a line in the output. Therefore the use of 

  @{ML "(space_explode \"\\n\" txt)" for txt} 

  \begin{readmore}

  For more information about options of antiquotations see \rsccite{sec:antiq}).

  \end{readmore}

  Since we used the argument @{ML "Position.none"}, the compiler cannot give specific 

  information about the line number, in case an error is detected. We 

  can improve the code above slightly by writing 

*}

  (ML_Context.eval_in (SOME ctxt) false pos (ml_val code_txt);

text {*

  where in Lines 1 and 2 the positional information is properly treated.

  (FIXME: say something about OuterParse.position)

  We can now write in a document @{text "@{ML_checked \"2 + 3\"}"} in order to

  obtain @{ML_checked "2 + 3"} and be sure that this code compiles until

  somebody changes the definition of \mbox{@{ML "(op +)"}}.

  The second antiquotation we describe extends the first by allowing also to give

  a pattern that specifies what the result of the ML-code should be and to check 

  the consistency of the actual result with the given pattern. For this we are going 

  to implement the antiquotation  

  @{text [display] "@{ML_resp \"a_piece_of_code\" \"pattern\"}"}

  To add some convenience and also to deal with large outputs,

  the user can give a partial specification by giving the abbreviation 

  @{text [quotes] "\<dots>"}. For example @{text "(\<dots>,\<dots>)"} for a pair.

  Whereas in the antiquotation @{text "@{ML_checked \"piece_of_code\"}"} above, 

  we have sent the expression 

  @{text [quotes] "val _ = piece_of_code"} to the compiler, in the second the 

  wildcard @{text "_"} we will be replaced by a proper pattern. To do this we 

  need to replace the @{text [quotes] "\<dots>"} by 

  @{text [quotes] "_"}  before sending the code to the compiler. The following 

  function will do this:

*}

ML{*fun ml_pat (code_txt, pat) =

   let val pat' = 

         implode (map (fn "\<dots>" => "_" | s => s) (Symbol.explode pat))

   in 

     "val " ^ pat' ^ " = " ^ code_txt 

   end*}

text {* 

  Next we like to add a response indicator to the result using:

*}

ML{*fun add_resp_indicator pat =

  map (fn s => "> " ^ s) (space_explode "\n" pat) *}

text {* 

  The rest of the code of the antiquotation is

*}

  (ML_Context.eval_in (SOME ctxt) false pos (ml_pat (code_txt,pat));

   let 

     val output = (space_explode "\n" code_txt) @ (add_resp_indicator pat)

   in 

   end)

text {*

  This extended antiquotation allows us to write

  @{text [display] "@{ML_resp [display] \"true andalso false\" \"false\"}"}

  to obtain

  @{ML_resp [display] "true andalso false" "false"} 

  or 

  @{text [display] "@{ML_resp [display] \"let val i = 3 in (i * i,\"foo\") end\" \"(9,\<dots>)\"}"}

  to obtain

  @{ML_resp [display] "let val i = 3 in (i * i,\"foo\") end" "(9,\<dots>)"} 

  In both cases, the check by the compiler ensures that code and result match. A limitation

  of this antiquotation, however, is that the hints can only be given in case

  they can be constructed as a pattern. This excludes values that are abstract datatypes, like 

  theorems or cterms.

*}

end