(*  Title:      Pure/Tools/value.ML

    ID:         $Id$

    Author:     Florian Haftmann, TU Muenchen

Value command for different evaluators.

*)

signature VALUE =

sig

  val value: Proof.context -> term -> term

  val value_select: string -> Proof.context -> term -> term

  val value_cmd: string option -> string list -> string -> Toplevel.state -> unit

  val add_evaluator: string * (Proof.context -> term -> term) -> theory -> theory

end;

structure Value : VALUE =

struct

structure Evaluator = TheoryDataFun(

  type T = (string * (Proof.context -> term -> term)) list;

  val empty = [];

  val copy = I;

  val extend = I;

  fun merge pp = AList.merge (op =) (K true);

)

val add_evaluator = Evaluator.map o AList.update (op =);

fun value_select name ctxt =

  case AList.lookup (op =) (Evaluator.get (ProofContext.theory_of ctxt)) name

   of NONE => error ("No such evaluator: " ^ name)

    | SOME f => f ctxt;

fun value ctxt t = let val evaluators = Evaluator.get (ProofContext.theory_of ctxt)

  in if null evaluators then error "No evaluators"

  else let val (evaluators, (_, evaluator)) = split_last evaluators

    in case get_first (fn (_, f) => try (f ctxt) t) evaluators

     of SOME t' => t'

      | NONE => evaluator ctxt t

  end end;

fun value_cmd some_name modes raw_t state =

  let

    val ctxt = Toplevel.context_of state;

    val t = Syntax.read_term ctxt raw_t;

    val t' = case some_name

     of NONE => value ctxt t

      | SOME name => value_select name ctxt t;

    val ty' = Term.type_of t';

    val ctxt' = Variable.auto_fixes t ctxt;

    val p = PrintMode.with_modes modes (fn () =>

      Pretty.block [Pretty.quote (Syntax.pretty_term ctxt' t'), Pretty.fbrk,

        Pretty.str "::", Pretty.brk 1, Pretty.quote (Syntax.pretty_typ ctxt' ty')]) ();

  in Pretty.writeln p end;

local structure P = OuterParse and K = OuterKeyword in

val opt_modes = Scan.optional (P.$$$ "(" |-- P.!!! (Scan.repeat1 P.xname --| P.$$$ ")")) [];

val _ = OuterSyntax.improper_command "value" "evaluate and print term" K.diag

  (Scan.option (P.$$$ "[" |-- P.xname --| P.$$$ "]") -- opt_modes -- P.term

    >> (fn ((some_name, modes), t) => Toplevel.no_timing o Toplevel.keep

        (value_cmd some_name modes t)));

end; (*local*)

end;