(*  Title:      HOL/Code_Eval.thy

    Author:     Florian Haftmann, TU Muenchen

*)

header {* Term evaluation using the generic code generator *}

theory Code_Eval

imports Plain Typerep

begin

subsection {* Term representation *}

subsubsection {* Terms and class @{text term_of} *}

datatype "term" = dummy_term

definition Const :: "message_string \<Rightarrow> typerep \<Rightarrow> term" where

  "Const _ _ = dummy_term"

definition App :: "term \<Rightarrow> term \<Rightarrow> term" where

  "App _ _ = dummy_term"

code_datatype Const App

class term_of = typerep +

  fixes term_of :: "'a \<Rightarrow> term"

lemma term_of_anything: "term_of x \<equiv> t"

  by (rule eq_reflection) (cases "term_of x", cases t, simp)

subsubsection {* @{text term_of} instances *}

setup {*

let

  fun add_term_of tyco raw_vs thy =

    let

      val vs = map (fn (v, _) => (v, @{sort typerep})) raw_vs;

      val ty = Type (tyco, map TFree vs);

      val lhs = Const (@{const_name term_of}, ty --> @{typ term})

        $ Free ("x", ty);

      val rhs = @{term "undefined \<Colon> term"};

      val eq = HOLogic.mk_Trueprop (HOLogic.mk_eq (lhs, rhs));

      fun triv_name_of t = (fst o dest_Free o fst o strip_comb o fst

        o HOLogic.dest_eq o HOLogic.dest_Trueprop) t ^ "_triv";

    in

      thy

      |> TheoryTarget.instantiation ([tyco], vs, @{sort term_of})

      |> `(fn lthy => Syntax.check_term lthy eq)

      |-> (fn eq => Specification.definition (NONE, ((Binding.name (triv_name_of eq), []), eq)))

      |> snd

      |> Class.prove_instantiation_exit (K (Class.intro_classes_tac []))

    end;

  fun ensure_term_of (tyco, (raw_vs, _)) thy =

    let

      val need_inst = not (can (Sorts.mg_domain (Sign.classes_of thy) tyco) @{sort term_of})

        andalso can (Sorts.mg_domain (Sign.classes_of thy) tyco) @{sort typerep};

    in

      thy

      |> need_inst ? add_term_of tyco raw_vs

    end;

in

  Code.type_interpretation ensure_term_of

end

*}

setup {*

let

  fun mk_term_of_eq thy ty vs tyco (c, tys) =

    let

      val t = list_comb (Const (c, tys ---> ty),

        map Free (Name.names Name.context "a" tys));

      val (arg, rhs) = pairself (Thm.cterm_of thy o map_types Logic.unvarifyT o Logic.varify)

        (t, (map_aterms (fn t as Free (v, ty) => HOLogic.mk_term_of ty t | t => t) o HOLogic.reflect_term) t)

      val cty = Thm.ctyp_of thy ty;

    in

      @{thm term_of_anything}

      |> Drule.instantiate' [SOME cty] [SOME arg, SOME rhs]

      |> Thm.varifyT

    end;

  fun add_term_of_code tyco raw_vs raw_cs thy =

    let

      val vs = map (fn (v, _) => (v, @{sort typerep})) raw_vs;

      val ty = Type (tyco, map TFree vs);

      val cs = (map o apsnd o map o map_atyps)

        (fn TFree (v, _) => TFree (v, (the o AList.lookup (op =) vs) v)) raw_cs;

      val const = AxClass.param_of_inst thy (@{const_name term_of}, tyco);

      val eqs = map (mk_term_of_eq thy ty vs tyco) cs;

   in

      thy

      |> Code.del_eqns const

      |> fold Code.add_eqn eqs

    end;

  fun ensure_term_of_code (tyco, (raw_vs, cs)) thy =

    let

      val has_inst = can (Sorts.mg_domain (Sign.classes_of thy) tyco) @{sort term_of};

    in

      thy

      |> has_inst ? add_term_of_code tyco raw_vs cs

    end;

in

  Code.type_interpretation ensure_term_of_code

end

*}

subsubsection {* Code generator setup *}

lemmas [code del] = term.recs term.cases term.size

lemma [code, code del]: "eq_class.eq (t1\<Colon>term) t2 \<longleftrightarrow> eq_class.eq t1 t2" ..

lemma [code, code del]: "(term_of \<Colon> typerep \<Rightarrow> term) = term_of" ..

lemma [code, code del]: "(term_of \<Colon> term \<Rightarrow> term) = term_of" ..

lemma [code, code del]: "(term_of \<Colon> message_string \<Rightarrow> term) = term_of" ..

lemma [code, code del]:

  "(Code_Eval.term_of \<Colon> 'a::{type, term_of} Predicate.pred \<Rightarrow> Code_Eval.term) = Code_Eval.term_of" ..

lemma [code, code del]:

  "(Code_Eval.term_of \<Colon> 'a::{type, term_of} Predicate.seq \<Rightarrow> Code_Eval.term) = Code_Eval.term_of" ..

lemma term_of_char [unfolded typerep_fun_def typerep_char_def typerep_nibble_def, code]: "Code_Eval.term_of c =

    (let (n, m) = nibble_pair_of_char c

  in Code_Eval.App (Code_Eval.App (Code_Eval.Const (STR ''Pair'') (TYPEREP(nibble \<Rightarrow> nibble \<Rightarrow> char)))

    (Code_Eval.term_of n)) (Code_Eval.term_of m))"

  by (subst term_of_anything) rule 

code_type "term"

  (Eval "Term.term")

code_const Const and App

  (Eval "Term.Const/ (_, _)" and "Term.$/ (_, _)")

code_const "term_of \<Colon> message_string \<Rightarrow> term"

  (Eval "HOLogic.mk'_message'_string")

code_reserved Eval HOLogic

subsection {* Evaluation setup *}

ML {*

signature EVAL =

sig

  val eval_ref: (unit -> term) option ref

  val eval_term: theory -> term -> term

end;

structure Eval : EVAL =

struct

val eval_ref = ref (NONE : (unit -> term) option);

fun eval_term thy t =

  Code_ML.eval NONE ("Eval.eval_ref", eval_ref) I thy (HOLogic.mk_term_of (fastype_of t) t) [];

end;

*}

setup {*

  Value.add_evaluator ("code", Eval.eval_term o ProofContext.theory_of)

*}

subsubsection {* Syntax *}

print_translation {*

let

  val term = Const ("<TERM>", dummyT);

  fun tr1' [_, _] = term;

  fun tr2' [] = term;

in

  [(@{const_syntax Const}, tr1'),

    (@{const_syntax App}, tr1'),

    (@{const_syntax dummy_term}, tr2')]

end

*}

hide const dummy_term

hide (open) const Const App

hide (open) const term_of

end