src/HOL/Tools/Function/mutual.ML

removed support for tail-recursion from function package (now implemented by partial_function)

(*  Title:      HOL/Tools/Function/mutual.ML
    Author:     Alexander Krauss, TU Muenchen

Mutual recursive function definitions.
*)

signature FUNCTION_MUTUAL =
sig

  val prepare_function_mutual : Function_Common.function_config
    -> string (* defname *)
    -> ((string * typ) * mixfix) list
    -> term list
    -> local_theory
    -> ((thm (* goalstate *)
        * (thm -> Function_Common.function_result) (* proof continuation *)
       ) * local_theory)

end


structure Function_Mutual: FUNCTION_MUTUAL =
struct

open Function_Lib
open Function_Common

type qgar = string * (string * typ) list * term list * term list * term

datatype mutual_part = MutualPart of
 {i : int,
  i' : int,
  fvar : string * typ,
  cargTs: typ list,
  f_def: term,

  f: term option,
  f_defthm : thm option}

datatype mutual_info = Mutual of
 {n : int,
  n' : int,
  fsum_var : string * typ,

  ST: typ,
  RST: typ,

  parts: mutual_part list,
  fqgars: qgar list,
  qglrs: ((string * typ) list * term list * term * term) list,

  fsum : term option}

fun mutual_induct_Pnames n =
  if n < 5 then fst (chop n ["P","Q","R","S"])
  else map (fn i => "P" ^ string_of_int i) (1 upto n)

fun get_part fname =
  the o find_first (fn (MutualPart {fvar=(n,_), ...}) => n = fname)

(* FIXME *)
fun mk_prod_abs e (t1, t2) =
  let
    val bTs = rev (map snd e)
    val T1 = fastype_of1 (bTs, t1)
    val T2 = fastype_of1 (bTs, t2)
  in
    HOLogic.pair_const T1 T2 $ t1 $ t2
  end

fun analyze_eqs ctxt defname fs eqs =
  let
    val num = length fs
    val fqgars = map (split_def ctxt (K true)) eqs
    val arity_of = map (fn (fname,_,_,args,_) => (fname, length args)) fqgars
      |> AList.lookup (op =) #> the

    fun curried_types (fname, fT) =
      let
        val (caTs, uaTs) = chop (arity_of fname) (binder_types fT)
      in
        (caTs, uaTs ---> body_type fT)
      end

    val (caTss, resultTs) = split_list (map curried_types fs)
    val argTs = map (foldr1 HOLogic.mk_prodT) caTss

    val dresultTs = distinct (op =) resultTs
    val n' = length dresultTs

    val RST = Balanced_Tree.make (uncurry SumTree.mk_sumT) dresultTs
    val ST = Balanced_Tree.make (uncurry SumTree.mk_sumT) argTs

    val fsum_type = ST --> RST

    val ([fsum_var_name], _) = Variable.add_fixes [ defname ^ "_sum" ] ctxt
    val fsum_var = (fsum_var_name, fsum_type)

    fun define (fvar as (n, _)) caTs resultT i =
      let
        val vars = map_index (fn (j,T) => Free ("x" ^ string_of_int j, T)) caTs (* FIXME: Bind xs properly *)
        val i' = find_index (fn Ta => Ta = resultT) dresultTs + 1

        val f_exp = SumTree.mk_proj RST n' i' (Free fsum_var $ SumTree.mk_inj ST num i (foldr1 HOLogic.mk_prod vars))
        val def = Term.abstract_over (Free fsum_var, fold_rev lambda vars f_exp)

        val rew = (n, fold_rev lambda vars f_exp)
      in
        (MutualPart {i=i, i'=i', fvar=fvar,cargTs=caTs,f_def=def,f=NONE,f_defthm=NONE}, rew)
      end

    val (parts, rews) = split_list (map4 define fs caTss resultTs (1 upto num))

    fun convert_eqs (f, qs, gs, args, rhs) =
      let
        val MutualPart {i, i', ...} = get_part f parts
      in
        (qs, gs, SumTree.mk_inj ST num i (foldr1 (mk_prod_abs qs) args),
         SumTree.mk_inj RST n' i' (replace_frees rews rhs)
         |> Envir.beta_norm)
      end

    val qglrs = map convert_eqs fqgars
  in
    Mutual {n=num, n'=n', fsum_var=fsum_var, ST=ST, RST=RST,
      parts=parts, fqgars=fqgars, qglrs=qglrs, fsum=NONE}
  end

fun define_projections fixes mutual fsum lthy =
  let
    fun def ((MutualPart {i=i, i'=i', fvar=(fname, fT), cargTs, f_def, ...}), (_, mixfix)) lthy =
      let
        val ((f, (_, f_defthm)), lthy') =
          Local_Theory.define
            ((Binding.name fname, mixfix),
              ((Binding.conceal (Binding.name (fname ^ "_def")), []),
              Term.subst_bound (fsum, f_def))) lthy
      in
        (MutualPart {i=i, i'=i', fvar=(fname, fT), cargTs=cargTs, f_def=f_def,
           f=SOME f, f_defthm=SOME f_defthm },
         lthy')
      end

    val Mutual { n, n', fsum_var, ST, RST, parts, fqgars, qglrs, ... } = mutual
    val (parts', lthy') = fold_map def (parts ~~ fixes) lthy
  in
    (Mutual { n=n, n'=n', fsum_var=fsum_var, ST=ST, RST=RST, parts=parts',
       fqgars=fqgars, qglrs=qglrs, fsum=SOME fsum },
     lthy')
  end

fun in_context ctxt (f, pre_qs, pre_gs, pre_args, pre_rhs) F =
  let
    val thy = ProofContext.theory_of ctxt

    val oqnames = map fst pre_qs
    val (qs, _) = Variable.variant_fixes oqnames ctxt
      |>> map2 (fn (_, T) => fn n => Free (n, T)) pre_qs

    fun inst t = subst_bounds (rev qs, t)
    val gs = map inst pre_gs
    val args = map inst pre_args
    val rhs = inst pre_rhs

    val cqs = map (cterm_of thy) qs
    val ags = map (Thm.assume o cterm_of thy) gs

    val import = fold Thm.forall_elim cqs
      #> fold Thm.elim_implies ags

    val export = fold_rev (Thm.implies_intr o cprop_of) ags
      #> fold_rev forall_intr_rename (oqnames ~~ cqs)
  in
    F ctxt (f, qs, gs, args, rhs) import export
  end

fun recover_mutual_psimp all_orig_fdefs parts ctxt (fname, _, _, args, rhs)
  import (export : thm -> thm) sum_psimp_eq =
  let
    val (MutualPart {f=SOME f, ...}) = get_part fname parts

    val psimp = import sum_psimp_eq
    val (simp, restore_cond) =
      case cprems_of psimp of
        [] => (psimp, I)
      | [cond] => (Thm.implies_elim psimp (Thm.assume cond), Thm.implies_intr cond)
      | _ => raise General.Fail "Too many conditions"

  in
    Goal.prove ctxt [] []
      (HOLogic.Trueprop $ HOLogic.mk_eq (list_comb (f, args), rhs))
      (fn _ => (Local_Defs.unfold_tac ctxt all_orig_fdefs)
         THEN EqSubst.eqsubst_tac ctxt [0] [simp] 1
         THEN (simp_tac (simpset_of ctxt)) 1) (* FIXME: global simpset?!! *)
    |> restore_cond
    |> export
  end

fun mk_applied_form ctxt caTs thm =
  let
    val thy = ProofContext.theory_of ctxt
    val xs = map_index (fn (i,T) => cterm_of thy (Free ("x" ^ string_of_int i, T))) caTs (* FIXME: Bind xs properly *)
  in
    fold (fn x => fn thm => Thm.combination thm (Thm.reflexive x)) xs thm
    |> Conv.fconv_rule (Thm.beta_conversion true)
    |> fold_rev Thm.forall_intr xs
    |> Thm.forall_elim_vars 0
  end

fun mutual_induct_rules lthy induct all_f_defs (Mutual {n, ST, parts, ...}) =
  let
    val cert = cterm_of (ProofContext.theory_of lthy)
    val newPs =
      map2 (fn Pname => fn MutualPart {cargTs, ...} =>
          Free (Pname, cargTs ---> HOLogic.boolT))
        (mutual_induct_Pnames (length parts)) parts

    fun mk_P (MutualPart {cargTs, ...}) P =
      let
        val avars = map_index (fn (i,T) => Var (("a", i), T)) cargTs
        val atup = foldr1 HOLogic.mk_prod avars
      in
        HOLogic.tupled_lambda atup (list_comb (P, avars))
      end

    val Ps = map2 mk_P parts newPs
    val case_exp = SumTree.mk_sumcases HOLogic.boolT Ps

    val induct_inst =
      Thm.forall_elim (cert case_exp) induct
      |> full_simplify SumTree.sumcase_split_ss
      |> full_simplify (HOL_basic_ss addsimps all_f_defs)

    fun project rule (MutualPart {cargTs, i, ...}) k =
      let
        val afs = map_index (fn (j,T) => Free ("a" ^ string_of_int (j + k), T)) cargTs (* FIXME! *)
        val inj = SumTree.mk_inj ST n i (foldr1 HOLogic.mk_prod afs)
      in
        (rule
         |> Thm.forall_elim (cert inj)
         |> full_simplify SumTree.sumcase_split_ss
         |> fold_rev (Thm.forall_intr o cert) (afs @ newPs),
         k + length cargTs)
      end
  in
    fst (fold_map (project induct_inst) parts 0)
  end

fun mk_partial_rules_mutual lthy inner_cont (m as Mutual {parts, fqgars, ...}) proof =
  let
    val result = inner_cont proof
    val FunctionResult {G, R, cases, psimps, simple_pinducts=[simple_pinduct],
      termination, domintros, ...} = result

    val (all_f_defs, fs) =
      map (fn MutualPart {f_defthm = SOME f_def, f = SOME f, cargTs, ...} =>
        (mk_applied_form lthy cargTs (Thm.symmetric f_def), f))
      parts
      |> split_list

    val all_orig_fdefs =
      map (fn MutualPart {f_defthm = SOME f_def, ...} => f_def) parts

    fun mk_mpsimp fqgar sum_psimp =
      in_context lthy fqgar (recover_mutual_psimp all_orig_fdefs parts) sum_psimp

    val rew_ss = HOL_basic_ss addsimps all_f_defs
    val mpsimps = map2 mk_mpsimp fqgars psimps
    val minducts = mutual_induct_rules lthy simple_pinduct all_f_defs m
    val mtermination = full_simplify rew_ss termination
    val mdomintros = Option.map (map (full_simplify rew_ss)) domintros
  in
    FunctionResult { fs=fs, G=G, R=R,
      psimps=mpsimps, simple_pinducts=minducts,
      cases=cases, termination=mtermination,
      domintros=mdomintros}
  end

fun prepare_function_mutual config defname fixes eqss lthy =
  let
    val mutual as Mutual {fsum_var=(n, T), qglrs, ...} =
      analyze_eqs lthy defname (map fst fixes) (map Envir.beta_eta_contract eqss)

    val ((fsum, goalstate, cont), lthy') =
      Function_Core.prepare_function config defname [((n, T), NoSyn)] qglrs lthy

    val (mutual', lthy'') = define_projections fixes mutual fsum lthy'

    val mutual_cont = mk_partial_rules_mutual lthy'' cont mutual'
  in
    ((goalstate, mutual_cont), lthy'')
  end

end