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

  Below we give the code for two 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 \"\<dots>\"}"}. This

  antiquotation takes a piece of code as argument; this code is then checked

  by sending the ML-expression @{text [quotes] "val _ = \<dots>"} containing the

  given code to the ML-compiler (i.e.~the function @{ML "ML_Context.eval_in"}

  in the snippet below). The code for @{text "@{ML_checked \"\<dots>\"}"} is as

  follows:

ML %linenumbers {*fun ml_val txt = "val _ = " ^ txt

  (ML_Context.eval_in (SOME ctxt) false Position.none (ml txt); 

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

  in this case the code. This code is send to the ML-compiler in the line 4.  

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

  "ThyOutput.output_list (fn _ => fn s => Pretty.str s)"} in the next line pretty prints the

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

  string correspond to a line (therefore the @{ML_open "(space_explode \"\\n\" txt)" for txt} 

  which produces this list).  There are a number of options for antiquotations

  that are observed by @{ML ThyOutput.output_list} when printing the code (for

  example @{text "[display]"}, @{text "[quotes]"} and @{text "[source]"}).

  \begin{readmore}

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

  \end{readmore}

  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 @{ML "(op +)"}.

  The second antiquotation extends the first by allowing to also give

  hints what the result of the ML-code is and check consistency of these

  hints. For this we use the antiquotation  @{text "@{ML_response \"\<dots>\" \"\<dots>\"}"}

  whose first argument is the ML-code and the second is the result. 

  In the antiquotation @{text "@{ML_checked \"\<dots>\"}"} we send the expresion 

  @{text [quotes] "val _ = \<dots>"} to the compiler. Now we will use the hints

  to construct a pattern for the @{text "_"}. To add some convenince we allow

  the user to give partial hints using @{text "\<dots>"}, which however need to

  be replaced by @{text "_"} before sending the code to the compiler. The

  function 

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

in "val " ^ pat' ^ " = " ^ rhs end;

*}

text {* 

  will do this. Next we like to add a response indicator to the result using:

*}

ML {*

*}

text {* 

  The rest of the code of the antiquotation is

  *}

ML {*

     ThyOutput.args 

      (Scan.lift (OuterParse.position (Args.name -- Args.name))) 

      (output_ml_response ml_pat))]

text {*

  This extended antiquotation allows us to write 

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

  to obtain

  or 

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

  to obtain

@{ML_response [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 is that the hints can only be given for results that can actually

  be constructed as a pattern. This excludes values that are abstract types, like 

  theorems or cterms.

*}