diff -r 1860f016886d -r 15a4b2cf8c34 src/Tools/value.ML
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Tools/value.ML	Wed Dec 03 15:58:44 2008 +0100
@@ -0,0 +1,66 @@
+(*  Title:      Pure/Tools/value.ML
+    Author:     Florian Haftmann, TU Muenchen
+
+Generic value command for arbitrary 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;