src/HOL/Sexp.thy

minor fix: instance now raises error if witness axioms don't exist;

(*  Title: 	HOL/Sexp
    ID:         $Id$
    Author: 	Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   1992  University of Cambridge

S-expressions, general binary trees for defining recursive data structures
*)

Sexp = Univ +
consts
  sexp      :: "'a item set"

  sexp_case :: "['a=>'b, nat=>'b, ['a item, 'a item]=>'b, 
                'a item] => 'b"

  sexp_rec  :: "['a item, 'a=>'b, nat=>'b, 	
                ['a item, 'a item, 'b, 'b]=>'b] => 'b"
  
  pred_sexp :: "('a item * 'a item)set"

inductive "sexp"
  intrs
    LeafI  "Leaf(a): sexp"
    NumbI  "Numb(a): sexp"
    SconsI "[| M: sexp;  N: sexp |] ==> M$N : sexp"

defs

  sexp_case_def	
   "sexp_case c d e M == @ z. (? x.   M=Leaf(x) & z=c(x))  
                           | (? k.   M=Numb(k) & z=d(k))  
                           | (? N1 N2. M = N1 $ N2  & z=e N1 N2)"

  pred_sexp_def
     "pred_sexp == UN M: sexp. UN N: sexp. {(M, M$N), (N, M$N)}"

  sexp_rec_def
   "sexp_rec M c d e == wfrec pred_sexp M  
             (%M g. sexp_case c d (%N1 N2. e N1 N2 (g N1) (g N2)) M)"
end