theory Antiquotes

imports "../Appendix"

begin

section {* Useful Document Antiquotations\label{rec:docantiquotations} *}

text {*

  {\bf Problem:} 

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

  {\bf Solution:} This can be achieved with 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 on the Isabelle level

*}

print_antiquotations

text {*

  you obtain a list of all currently available document antiquotations and

  their options.  

  Below we will give the code for two additional document

  antiquotations both of which are intended to typeset ML-code. The crucial point

  of these document antiquotations is that they not just print the ML-code, but also 

  check whether it compiles. This will provide a sanity check for the code

  and also allows you 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_source_in"} in Line 7 below). The complete code of the

  document antiquotation is as follows:

*}

let

end

setup {* ml_checked_setup *}

text {*

  The parser @{ML "(Scan.lift Args.name)"} in Line 7 parses a string, in this

  case the code, and then calls the function @{ML output_ml}. As mentioned

  before, the parsed code is sent to the ML-compiler in Line 4 using the

  function @{ML ml_val}, which constructs the appropriate ML-expression, and

  using @{ML "eval_in" in ML_Context}, which calls the compiler.  If the code is

  ``approved'' by the compiler, then the output function @{ML "output" in

  that the code is a list of (pretty)strings where each string correspond to a

  line in the output. Therefore the use of @{ML "(space_explode \"\\n\" txt)"

  for txt} which produces such a list according to linebreaks.  There are a

  number of options for antiquotations that are observed by the function 

  Line 7 sets up the new document antiquotation.

  \begin{readmore}

  For more information about options of document 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 

*}

let

  val srcpos = {delimited = false, pos = pos, text = ml_val code_txt}

in

  (ML_Context.eval_source_in (SOME ctxt) ML_Compiler.flags srcpos;

end

val ml_checked_setup2 = Thy_Output.antiquotation @{binding "ML_checked2"}

         (Scan.lift (Parse.position Args.name)) output_ml *}

setup {* ml_checked_setup2 *}

text {*

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

  parser @{ML Parse.position} encodes the positional information in the 

  result.

  We can now write @{text "@{ML_checked2 \"2 + 3\"}"} in a document in order to

  somebody changes the definition of addition.

  The second document antiquotation we describe extends the first by a pattern

  that specifies what the result of the ML-code should be and checks the

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

  going to implement the document antiquotation:

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

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

  give a partial specification by using ellipses. For example @{text "(\<dots>, \<dots>)"}

  for specifying a pair.  In order to check consistency between the pattern

  and the output of the code, we have to change the ML-expression that is sent 

  to the compiler: in @{text "ML_checked2"} we sent the expression @{text [quotes]

  "val _ = a_piece_of_code"} to the compiler; now the wildcard @{text "_"}

  must be be replaced by the given pattern. However, we have to remove all

  ellipses from it and replace them by @{text [quotes] "_"}. The following 

  function will do this:

*}

let val pat' = 

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

in 

end*}

text {* 

  Next we add a response indicator to the result using:

*}

ML %grayML{*fun add_resp pat = map (fn s => "> " ^ s) pat*}

text {* 

  The rest of the code of @{text "ML_resp"} is: 

*}

ML %linenosgray{*fun output_ml_resp {context = ctxt, ...} ((code_txt, pat), pos) = 

  (let

     val srcpos = {delimited = false, text = ml_pat (code_txt, pat), pos = pos}

   in

     ML_Context.eval_source_in (SOME ctxt) ML_Compiler.flags srcpos 

   end;

   let 

     val code_output = space_explode "\n" code_txt 

     val resp_output = add_resp (space_explode "\n" pat)

   in 

     Thy_Output.output ctxt (map Pretty.str (code_output @ resp_output)) 

   end)

val ml_resp_setup = Thy_Output.antiquotation @{binding "ML_resp"} 

             output_ml_resp*}

  the compiler (Line~2), the lines about

  the output (Lines 4 to 7) and the parser in the setup (Line 11). Now 

  you can 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

  In both cases, the check by the compiler ensures that code and result

  match. A limitation of this document antiquotation, however, is that the

  pattern can only be given for values that can be constructed. This excludes

  values that are abstract datatypes, like @{ML_type thm}s and @{ML_type cterm}s.

*}

end