ind_syntax.ML

Added headers and made various small mods.

(*  Title: 	HOL/ind_syntax.ML
    ID:         $Id$
    Author: 	Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   1994  University of Cambridge

Abstract Syntax functions for Inductive Definitions
See also ../Pure/section-utils.ML
*)

(*The structure protects these items from redeclaration (somewhat!).  The 
  datatype definitions in theory files refer to these items by name!
*)
structure Ind_Syntax =
struct

(** Abstract syntax definitions for HOL **)

val termC: class = "term";
val termS: sort = [termC];

val termTVar = TVar(("'a",0),termS);

val boolT = Type("bool",[]);
val unitT = Type("unit",[]);

val conj = Const("op &", [boolT,boolT]--->boolT)
and disj = Const("op |", [boolT,boolT]--->boolT)
and imp = Const("op -->", [boolT,boolT]--->boolT);

fun eq_const T = Const("op =", [T,T]--->boolT);

fun mk_set T = Type("set",[T]);

fun dest_set (Type("set",[T])) = T
  | dest_set _                 = error "dest_set: set type expected"

fun mk_mem (x,A) = 
  let val setT = fastype_of A
  in  Const("op :", [dest_set setT, setT]--->boolT) $ x $ A
  end;

fun Int_const T = 
  let val sT = mk_set T
  in  Const("op Int", [sT,sT]--->sT)  end;

fun exists_const T = Const("Ex", [T-->boolT]--->boolT);
fun mk_exists (Free(x,T),P) = exists_const T $ (absfree (x,T,P));

fun all_const T = Const("All", [T-->boolT]--->boolT);
fun mk_all (Free(x,T),P) = all_const T $ (absfree (x,T,P));

(*Creates All(%v.v:A --> P(v)) rather than Ball(A,P) *)
fun mk_all_imp (A,P) = 
  let val T = dest_set (fastype_of A)
  in  all_const T $ Abs("v", T, imp $ (mk_mem (Bound 0, A)) $ (P $ Bound 0))
  end;

(** Cartesian product type **)

fun mk_prod (T1,T2) = Type("*", [T1,T2]);

(*Maps the type T1*...*Tn to [T1,...,Tn], if nested to the right*)
fun factors (Type("*", [T1,T2])) = T1 :: factors T2
  | factors T                    = [T];

(*Make a correctly typed ordered pair*)
fun mk_Pair (t1,t2) = 
  let val T1 = fastype_of t1
      and T2 = fastype_of t2
  in  Const("Pair", [T1, T2] ---> mk_prod(T1,T2)) $ t1 $ t2  end;
   
fun split_const(Ta,Tb,Tc) = 
    Const("split", [[Ta,Tb]--->Tc, mk_prod(Ta,Tb)] ---> Tc);

(*Given u expecting arguments of types [T1,...,Tn], create term of 
  type T1*...*Tn => Tc using split.  Here * associates to the LEFT*)
fun ap_split_l Tc u [ ]   = Abs("null", unitT, u)
  | ap_split_l Tc u [_]   = u
  | ap_split_l Tc u (Ta::Tb::Ts) = ap_split_l Tc (split_const(Ta,Tb,Tc) $ u) 
                                              (mk_prod(Ta,Tb) :: Ts);

(*Given u expecting arguments of types [T1,...,Tn], create term of 
  type T1*...*Tn => i using split.  Here * associates to the RIGHT*)
fun ap_split Tc u [ ]   = Abs("null", unitT, u)
  | ap_split Tc u [_]   = u
  | ap_split Tc u [Ta,Tb] = split_const(Ta,Tb,Tc) $ u
  | ap_split Tc u (Ta::Ts) = 
      split_const(Ta, foldr1 mk_prod Ts, Tc) $ 
      (Abs("v", Ta, ap_split Tc (u $ Bound(length Ts - 2)) Ts));

(** Disjoint sum type **)

fun mk_sum (T1,T2) = Type("+", [T1,T2]);
val Inl	= Const("Inl", dummyT)
and Inr	= Const("Inr", dummyT);		(*correct types added later!*)
(*val elim	= Const("case", [iT-->iT, iT-->iT, iT]--->iT)*)

fun summands (Type("+", [T1,T2])) = summands T1 @ summands T2
  | summands T                    = [T];

(*Given the destination type, fills in correct types of an Inl/Inr nest*)
fun mend_sum_types (h,T) =
    (case (h,T) of
	 (Const("Inl",_) $ h1, Type("+", [T1,T2])) =>
	     Const("Inl", T1 --> T) $ (mend_sum_types (h1, T1))
       | (Const("Inr",_) $ h2, Type("+", [T1,T2])) =>
	     Const("Inr", T2 --> T) $ (mend_sum_types (h2, T2))
       | _ => h);

fun Collect_const T = Const("Collect", [T-->boolT] ---> mk_set T);
fun mk_Collect (a,T,t) = Collect_const T $ absfree(a, T, t);

val Trueprop = Const("Trueprop",boolT-->propT);
fun mk_tprop P = Trueprop $ P;


(*simple error-checking in the premises of an inductive definition*)
fun chk_prem rec_hd (Const("op &",_) $ _ $ _) =
	error"Premises may not be conjuctive"
  | chk_prem rec_hd (Const("op :",_) $ t $ X) = 
	deny (Logic.occs(rec_hd,t)) "Recursion term on left of member symbol"
  | chk_prem rec_hd t = 
	deny (Logic.occs(rec_hd,t)) "Recursion term in side formula";

(*Return the conclusion of a rule, of the form t:X*)
fun rule_concl rl = 
    let val Const("Trueprop",_) $ (Const("op :",_) $ t $ X) = 
		Logic.strip_imp_concl rl
    in  (t,X)  end;

(*As above, but return error message if bad*)
fun rule_concl_msg sign rl = rule_concl rl
    handle Bind => error ("Ill-formed conclusion of introduction rule: " ^ 
			  Sign.string_of_term sign rl);

(*For simplifying the elimination rule*)
val sumprod_free_SEs = 
    Pair_inject ::
    map make_elim [Inl_neq_Inr, Inr_neq_Inl, Inl_inject, Inr_inject];

(*For deriving cases rules.  
  read_instantiate replaces a propositional variable by a formula variable*)
val equals_CollectD = 
    read_instantiate [("W","?Q")]
        (make_elim (equalityD1 RS subsetD RS CollectD));

(*Delete needless equality assumptions*)
val refl_thin = prove_goal HOL.thy "!!P. [| a=a;  P |] ==> P"
     (fn _ => [assume_tac 1]);

end;