src/HOL/Library/Eval.thy

+(*  Title:      HOL/Library/Eval.thy
+    ID:         $Id$
+    Author:     Florian Haftmann, TU Muenchen
+*)
+
+header {* A simple term evaluation mechanism *}
+
+theory Eval
+imports Pure_term
+begin
+
+subsection {* The typ_of class *}
+
+class typ_of = type +
+  fixes typ_of :: "'a itself \<Rightarrow> typ"
+
+ML {*
+structure TypOf =
+struct
+
+val class_typ_of = Sign.intern_class @{theory} "typ_of";
+
+fun term_typ_of_type ty =
+  Const (@{const_name typ_of}, Term.itselfT ty --> @{typ typ})
+    $ Logic.mk_type ty;
+
+fun mk_typ_of_def ty =
+  let
+    val lhs = Const (@{const_name typ_of}, Term.itselfT ty --> @{typ typ})
+      $ Free ("x", Term.itselfT ty)
+    val rhs = Pure_term.mk_typ (fn v => term_typ_of_type (TFree v)) ty
+  in Logic.mk_equals (lhs, rhs) end;
+
+end;
+*}
+
+setup {*
+let
+  fun mk arities _ thy =
+    (maps (fn (tyco, asorts, _) => [(("", []), TypOf.mk_typ_of_def
+      (Type (tyco,
+        map TFree (Name.names Name.context "'a" asorts))))]) arities, thy);
+  fun hook specs =
+    DatatypeCodegen.prove_codetypes_arities (ClassPackage.intro_classes_tac [])
+      (map (fn (tyco, (is_dt, _)) => (tyco, is_dt)) specs)
+      [TypOf.class_typ_of] mk ((K o K) I)
+in DatatypeCodegen.add_codetypes_hook_bootstrap hook end
+*}
+
+
+subsection {* term_of class *}
+
+class term_of = typ_of +
+  constrains typ_of :: "'a itself \<Rightarrow> typ"
+  fixes term_of :: "'a \<Rightarrow> term"
+
+ML {*
+structure TermOf =
+struct
+
+local
+  fun term_term_of ty =
+    Const (@{const_name term_of}, ty --> @{typ term});
+in
+  val class_term_of = Sign.intern_class @{theory} "term_of";
+  fun mk_terms_of_defs vs (tyco, cs) =
+    let
+      val dty = Type (tyco, map TFree vs);
+      fun mk_eq c =
+        let
+          val lhs : term = term_term_of dty $ c;
+          val rhs : term = Pure_term.mk_term
+            (fn (v, ty) => term_term_of ty $ Free (v, ty))
+            (Pure_term.mk_typ (fn (v, sort) => TypOf.term_typ_of_type (TFree (v, sort)))) c
+        in
+          HOLogic.mk_eq (lhs, rhs)
+        end;
+    in map mk_eq cs end;
+  fun mk_term_of t =
+    term_term_of (Term.fastype_of t) $ t;
+end;
+
+end;
+*}
+
+setup {*
+let
+  fun thy_note ((name, atts), thms) =
+    PureThy.add_thmss [((name, thms), atts)] #-> (fn [thms] => pair (name, thms));
+  fun thy_def ((name, atts), t) =
+    PureThy.add_defs_i false [((name, t), atts)] #-> (fn [thm] => pair (name, thm));
+  fun mk arities css thy =
+    let
+      val (_, asorts, _) :: _ = arities;
+      val vs = Name.names Name.context "'a" asorts;
+      val defs = map (TermOf.mk_terms_of_defs vs) css;
+      val defs' = (map (pair ("", []) o ObjectLogic.ensure_propT thy) o flat) defs;
+    in
+      thy
+      |> PrimrecPackage.gen_primrec thy_note thy_def "" defs'
+      |> snd
+    end;
+  fun hook specs =
+    if (fst o hd) specs = (fst o dest_Type) @{typ typ} then I
+    else
+      DatatypeCodegen.prove_codetypes_arities (ClassPackage.intro_classes_tac [])
+      (map (fn (tyco, (is_dt, _)) => (tyco, is_dt)) specs)
+      [TermOf.class_term_of] ((K o K o pair) []) mk
+in DatatypeCodegen.add_codetypes_hook_bootstrap hook end
+*}
+
+text {* Disable for characters and ml_strings *}
+
+code_const "typ_of \<Colon> char itself \<Rightarrow> typ" and "term_of \<Colon> char \<Rightarrow> term"
+  (SML "!((_); raise Fail \"typ'_of'_char\")"
+    and "!((_); raise Fail \"term'_of'_char\")")
+  (OCaml "!((_); failwith \"typ'_of'_char\")"
+    and "!((_); failwith \"term'_of'_char\")")
+  (Haskell "error/ \"typ'_of'_char\""
+    and "error/ \"term'_of'_char\"")
+
+code_const "term_of \<Colon> ml_string \<Rightarrow> term"
+  (SML "!((_); raise Fail \"term'_of'_ml'_string\")")
+  (OCaml "!((_); failwith \"term'_of'_ml'_string\")")
+
+subsection {* Evaluation infrastructure *}
+
+ML {*
+signature EVAL =
+sig
+  val eval_term: theory -> term -> term
+  val term: string -> unit
+  val eval_ref: term option ref
+end;
+
+structure Eval : EVAL =
+struct
+
+val eval_ref = ref (NONE : term option);
+
+fun eval_term thy t =
+  CodegenPackage.eval_term
+    thy (("Eval.eval_ref", eval_ref), TermOf.mk_term_of t);
+
+fun term t =
+  let
+    val thy = the_context ();
+    val t = eval_term thy (Sign.read_term thy t);
+  in (writeln o Sign.string_of_term thy) t end;
+
+end;
+*}
+
+end