author  wenzelm 
Sat, 14 Apr 2007 17:36:05 +0200  
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parent 22255  8fcd11cb9be7 
child 23222  daca4731942f 
permissions  rwrr 
12784  1 
(* Title: Pure/pattern.ML 
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ID: $Id$ 
12784  3 
Author: Tobias Nipkow, Christine Heinzelmann, and Stefan Berghofer 
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Unification of HigherOrder Patterns. 

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See also: 

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Tobias Nipkow. Functional Unification of HigherOrder Patterns. 

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In Proceedings of the 8th IEEE Symposium Logic in Computer Science, 1993. 

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TODO: optimize red by specialcasing it 
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*) 
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2751  14 
infix aeconv; 
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0  16 
signature PATTERN = 
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sig 
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val trace_unify_fail: bool ref 
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val aeconv: term * term > bool 

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val eta_long: typ list > term > term 

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val eta_contract_atom: term > term 

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val match: theory > term * term > Type.tyenv * Envir.tenv > Type.tyenv * Envir.tenv 
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val first_order_match: theory > term * term 
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> Type.tyenv * Envir.tenv > Type.tyenv * Envir.tenv 
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val matches: theory > term * term > bool 
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val equiv: theory > term * term > bool 
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val matches_subterm: theory > term * term > bool 
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val unify: theory > term * term > Envir.env > Envir.env 
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val first_order: term > bool 
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val pattern: term > bool 

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val rewrite_term: theory > (term * term) list > (term > term option) list > term > term 

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exception Unif 
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exception MATCH 

34 
exception Pattern 

14787  35 
end; 
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17203  37 
structure Pattern: PATTERN = 
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struct 
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40 
exception Unif; 

41 
exception Pattern; 

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val trace_unify_fail = ref false; 
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fun string_of_term thy env binders t = Sign.string_of_term thy 
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(Envir.norm_term env (subst_bounds(map Free binders,t))); 
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fun bname binders i = fst (nth binders i); 
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fun bnames binders is = space_implode " " (map (bname binders) is); 
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fun typ_clash thy (tye,T,U) = 
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if !trace_unify_fail 
17203  53 
then let val t = Sign.string_of_typ thy (Envir.norm_type tye T) 
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and u = Sign.string_of_typ thy (Envir.norm_type tye U) 

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in tracing("The following types do not unify:\n" ^ t ^ "\n" ^ u) end 
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else () 
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fun clash a b = 
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if !trace_unify_fail then tracing("Clash: " ^ a ^ " =/= " ^ b) else () 
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fun boundVar binders i = 
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"bound variable " ^ bname binders i ^ " (depth " ^ string_of_int i ^ ")"; 
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fun clashBB binders i j = 
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if !trace_unify_fail then clash (boundVar binders i) (boundVar binders j) 
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else () 
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fun clashB binders i s = 
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if !trace_unify_fail then clash (boundVar binders i) s 
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else () 
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17203  72 
fun proj_fail thy (env,binders,F,_,is,t) = 
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if !trace_unify_fail 
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then let val f = Term.string_of_vname F 
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val xs = bnames binders is 
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val u = string_of_term thy env binders t 
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val ys = bnames binders (subtract (op =) is (loose_bnos t)) 
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in tracing("Cannot unify variable " ^ f ^ 
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" (depending on bound variables " ^ xs ^ ")\nwith term " ^ u ^ 
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"\nTerm contains additional bound variable(s) " ^ ys) 
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end 
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else () 
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17203  84 
fun ocheck_fail thy (F,t,binders,env) = 
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if !trace_unify_fail 
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then let val f = Term.string_of_vname F 
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val u = string_of_term thy env binders t 
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in tracing("Variable " ^ f ^ " occurs in term\n" ^ u ^ 
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"\nCannot unify!\n") 
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end 
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else () 
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12784  93 
fun occurs(F,t,env) = 
15797  94 
let fun occ(Var (G, T)) = (case Envir.lookup (env, (G, T)) of 
15531  95 
SOME(t) => occ t 
96 
 NONE => F=G) 

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 occ(t1$t2) = occ t1 orelse occ t2 
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 occ(Abs(_,_,t)) = occ t 

99 
 occ _ = false 

100 
in occ t end; 

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102 

103 
fun mapbnd f = 

104 
let fun mpb d (Bound(i)) = if i < d then Bound(i) else Bound(f(id)+d) 

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 mpb d (Abs(s,T,t)) = Abs(s,T,mpb(d+1) t) 

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 mpb d ((u1 $ u2)) = (mpb d u1)$(mpb d u2) 
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 mpb _ atom = atom 
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in mpb 0 end; 
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fun idx [] j = raise Unif 
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 idx(i::is) j = if (i:int) =j then length is else idx is j; 
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fun mkabs (binders,is,t) = 

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let fun mk(i::is) = let val (x,T) = nth binders i 
12784  115 
in Abs(x,T,mk is) end 
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 mk [] = t 
117 
in mk is end; 

118 

119 
val incr = mapbnd (fn i => i+1); 

120 

121 
fun ints_of [] = [] 

12784  122 
 ints_of (Bound i ::bs) = 
0  123 
let val is = ints_of bs 
20672  124 
in if member (op =) is i then raise Pattern else i::is end 
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 ints_of _ = raise Pattern; 
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12232  127 
fun ints_of' env ts = ints_of (map (Envir.head_norm env) ts); 
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130 
fun app (s,(i::is)) = app (s$Bound(i),is) 

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 app (s,[]) = s; 

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fun red (Abs(_,_,s)) (i::is) js = red s is (i::js) 

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 red t [] [] = t 
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 red t is jn = app (mapbnd (nth jn) t,is); 
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(* split_type ([T1,....,Tn]> T,n,[]) = ([Tn,...,T1],T) *) 

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fun split_type (T,0,Ts) = (Ts,T) 

140 
 split_type (Type ("fun",[T1,T2]),n,Ts) = split_type (T2,n1,T1::Ts) 

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 split_type _ = error("split_type"); 
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fun type_of_G (env as Envir.Envir {iTs, ...}) (T,n,is) = 
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let val (Ts, U) = split_type (Envir.norm_type iTs T, n, []) 
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in map (nth Ts) is > U end; 
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fun mkhnf (binders,is,G,js) = mkabs (binders, is, app(G,js)); 

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fun mknewhnf(env,binders,is,F as (a,_),T,js) = 

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let val (env',G) = Envir.genvar a (env,type_of_G env (T,length is,js)) 
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in Envir.update (((F, T), mkhnf (binders, is, G, js)), env') end; 
0  152 

153 

154 
(* mk_proj_list(is) = [ is  k  1 <= k <= is and is[k] >= 0 ] *) 

155 
fun mk_proj_list is = 

19502  156 
let fun mk(i::is,j) = if is_some i then j :: mk(is,j1) else mk(is,j1) 
0  157 
 mk([],_) = [] 
158 
in mk(is,length is  1) end; 

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160 
fun proj(s,env,binders,is) = 

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let fun trans d i = if i<d then i else (idx is (id))+d; 

12232  162 
fun pr(s,env,d,binders) = (case Envir.head_norm env s of 
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Abs(a,T,t) => let val (t',env') = pr(t,env,d+1,((a,T)::binders)) 
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in (Abs(a,T,t'),env') end 

165 
 t => (case strip_comb t of 

166 
(c as Const _,ts) => 

167 
let val (ts',env') = prs(ts,env,d,binders) 

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in (list_comb(c,ts'),env') end 

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 (f as Free _,ts) => 

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let val (ts',env') = prs(ts,env,d,binders) 

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in (list_comb(f,ts'),env') end 

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 (Bound(i),ts) => 

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let val j = trans d i 

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val (ts',env') = prs(ts,env,d,binders) 
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in (list_comb(Bound j,ts'),env') end 
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 (Var(F as (a,_),Fty),ts) => 
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let val js = ints_of' env ts; 
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val js' = map (try (trans d)) js; 
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val ks = mk_proj_list js'; 
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val ls = map_filter I js' 
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val Hty = type_of_G env (Fty,length js,ks) 
0  182 
val (env',H) = Envir.genvar a (env,Hty) 
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val env'' = 

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Envir.update (((F, Fty), mkhnf (binders, js, H, ks)), env') 
0  185 
in (app(H,ls),env'') end 
186 
 _ => raise Pattern)) 

187 
and prs(s::ss,env,d,binders) = 

188 
let val (s',env1) = pr(s,env,d,binders) 

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val (ss',env2) = prs(ss,env1,d,binders) 

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in (s'::ss',env2) end 

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 prs([],env,_,_) = ([],env) 

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in if downto0(is,length binders  1) then (s,env) 

193 
else pr(s,env,0,binders) 

194 
end; 

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197 
(* mk_ff_list(is,js) = [ length(is)  k  1 <= k <= is and is[k] = js[k] ] *) 

12784  198 
fun mk_ff_list(is,js) = 
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let fun mk([],[],_) = [] 

16668  200 
 mk(i::is,j::js, k) = if (i:int) = j then k :: mk(is,js,k1) 
0  201 
else mk(is,js,k1) 
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 mk _ = error"mk_ff_list" 
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in mk(is,js,length is1) end; 
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fun flexflex1(env,binders,F,Fty,is,js) = 

206 
if is=js then env 

207 
else let val ks = mk_ff_list(is,js) 

208 
in mknewhnf(env,binders,is,F,Fty,ks) end; 

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fun flexflex2(env,binders,F,Fty,is,G,Gty,js) = 

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let fun ff(F,Fty,is,G as (a,_),Gty,js) = 

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if js subset_int is 
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then let val t= mkabs(binders,is,app(Var(G,Gty),map (idx is) js)) 
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in Envir.update (((F, Fty), t), env) end 
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else let val ks = is inter_int js 
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val Hty = type_of_G env (Fty,length is,map (idx is) ks) 
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val (env',H) = Envir.genvar a (env,Hty) 
218 
fun lam(is) = mkabs(binders,is,app(H,map (idx is) ks)); 

15797  219 
in Envir.update (((G, Gty), lam js), Envir.update (((F, Fty), lam is), env')) 
0  220 
end; 
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in if Term.indexname_ord (G,F) = LESS then ff(F,Fty,is,G,Gty,js) else ff(G,Gty,js,F,Fty,is) end 
0  222 

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fun unify_types thy (T,U) (env as Envir.Envir{asol,iTs,maxidx}) = 
0  224 
if T=U then env 
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else let val (iTs',maxidx') = Sign.typ_unify thy (U, T) (iTs, maxidx) 
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in Envir.Envir{asol=asol,maxidx=maxidx',iTs=iTs'} end 
17203  227 
handle Type.TUNIFY => (typ_clash thy (iTs,T,U); raise Unif); 
0  228 

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fun unif thy binders (s,t) env = case (Envir.head_norm env s, Envir.head_norm env t) of 
0  230 
(Abs(ns,Ts,ts),Abs(nt,Tt,tt)) => 
231 
let val name = if ns = "" then nt else ns 

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in unif thy ((name,Ts)::binders) (ts,tt) env end 
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 (Abs(ns,Ts,ts),t) => unif thy ((ns,Ts)::binders) (ts,(incr t)$Bound(0)) env 
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 (t,Abs(nt,Tt,tt)) => unif thy ((nt,Tt)::binders) ((incr t)$Bound(0),tt) env 
17203  235 
 p => cases thy (binders,env,p) 
0  236 

17203  237 
and cases thy (binders,env,(s,t)) = case (strip_comb s,strip_comb t) of 
12784  238 
((Var(F,Fty),ss),(Var(G,Gty),ts)) => 
12232  239 
if F = G then flexflex1(env,binders,F,Fty,ints_of' env ss,ints_of' env ts) 
240 
else flexflex2(env,binders,F,Fty,ints_of' env ss,G,Gty,ints_of' env ts) 

17203  241 
 ((Var(F,Fty),ss),_) => flexrigid thy (env,binders,F,Fty,ints_of' env ss,t) 
242 
 (_,(Var(F,Fty),ts)) => flexrigid thy (env,binders,F,Fty,ints_of' env ts,s) 

243 
 ((Const c,ss),(Const d,ts)) => rigidrigid thy (env,binders,c,d,ss,ts) 

244 
 ((Free(f),ss),(Free(g),ts)) => rigidrigid thy (env,binders,f,g,ss,ts) 

245 
 ((Bound(i),ss),(Bound(j),ts)) => rigidrigidB thy (env,binders,i,j,ss,ts) 

0  246 
 ((Abs(_),_),_) => raise Pattern 
247 
 (_,(Abs(_),_)) => raise Pattern 

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 ((Const(c,_),_),(Free(f,_),_)) => (clash c f; raise Unif) 
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 ((Const(c,_),_),(Bound i,_)) => (clashB binders i c; raise Unif) 
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 ((Free(f,_),_),(Const(c,_),_)) => (clash f c; raise Unif) 
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 ((Free(f,_),_),(Bound i,_)) => (clashB binders i f; raise Unif) 
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 ((Bound i,_),(Const(c,_),_)) => (clashB binders i c; raise Unif) 
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253 
 ((Bound i,_),(Free(f,_),_)) => (clashB binders i f; raise Unif) 
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254 

0  255 

17203  256 
and rigidrigid thy (env,binders,(a,Ta),(b,Tb),ss,ts) = 
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257 
if a<>b then (clash a b; raise Unif) 
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else env > unify_types thy (Ta,Tb) > fold (unif thy binders) (ss~~ts) 
0  259 

17203  260 
and rigidrigidB thy (env,binders,i,j,ss,ts) = 
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261 
if i <> j then (clashBB binders i j; raise Unif) 
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262 
else fold (unif thy binders) (ss~~ts) env 
0  263 

17203  264 
and flexrigid thy (params as (env,binders,F,Fty,is,t)) = 
265 
if occurs(F,t,env) then (ocheck_fail thy (F,t,binders,env); raise Unif) 

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266 
else (let val (u,env') = proj(t,env,binders,is) 
15797  267 
in Envir.update (((F, Fty), mkabs (binders, is, u)), env') end 
17203  268 
handle Unif => (proj_fail thy params; raise Unif)); 
0  269 

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fun unify thy = unif thy []; 
0  271 

272 

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(*Etacontract a term from outside: just enough to reduce it to an atom 
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274 
DOESN'T QUITE WORK! 
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275 
*) 
12784  276 
fun eta_contract_atom (t0 as Abs(a, T, body)) = 
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(case eta_contract2 body of 
12784  278 
body' as (f $ Bound 0) => 
279 
if loose_bvar1(f,0) then Abs(a,T,body') 

280 
else eta_contract_atom (incr_boundvars ~1 f) 

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281 
 _ => t0) 
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282 
 eta_contract_atom t = t 
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283 
and eta_contract2 (f$t) = f $ eta_contract_atom t 
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 eta_contract2 t = eta_contract_atom t; 
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285 

13998  286 
(* put a term into eta long beta normal form *) 
287 
fun eta_long Ts (Abs (s, T, t)) = Abs (s, T, eta_long (T :: Ts) t) 

288 
 eta_long Ts t = (case strip_comb t of 

289 
(Abs _, _) => eta_long Ts (Envir.beta_norm t) 

14787  290 
 (u, ts) => 
13998  291 
let 
292 
val Us = binder_types (fastype_of1 (Ts, t)); 

293 
val i = length Us 

294 
in list_abs (map (pair "x") Us, 

295 
list_comb (incr_boundvars i u, map (eta_long (rev Us @ Ts)) 

296 
(map (incr_boundvars i) ts @ map Bound (i  1 downto 0)))) 

297 
end); 

298 

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299 

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300 
(*Tests whether 2 terms are alpha/etaconvertible and have same type. 
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301 
Note that Consts and Vars may have more than one type.*) 
2751  302 
fun t aeconv u = aconv_aux (eta_contract_atom t, eta_contract_atom u) 
303 
and aconv_aux (Const(a,T), Const(b,U)) = a=b andalso T=U 

304 
 aconv_aux (Free(a,T), Free(b,U)) = a=b andalso T=U 

305 
 aconv_aux (Var(v,T), Var(w,U)) = eq_ix(v,w) andalso T=U 

12784  306 
 aconv_aux (Bound i, Bound j) = i=j 
2751  307 
 aconv_aux (Abs(_,T,t), Abs(_,U,u)) = (t aeconv u) andalso T=U 
12784  308 
 aconv_aux (f$t, g$u) = (f aeconv g) andalso (t aeconv u) 
2751  309 
 aconv_aux _ = false; 
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310 

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311 

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312 
(*** Matching ***) 
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313 

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314 
exception MATCH; 
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315 

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fun typ_match thy TU tyenv = Sign.typ_match thy TU tyenv 
16939  317 
handle Type.TYPE_MATCH => raise MATCH; 
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318 

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319 
(*Firstorder matching; 
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320 
The pattern and object may have variables in common. 
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321 
Instantiation does not affect the object, so matching ?a with ?a+1 works. 
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322 
Object is etacontracted on the fly (by etaexpanding the pattern). 
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323 
Precondition: the pattern is already etacontracted! 
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324 
Types are matched on the fly*) 
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325 
fun first_order_match thy = 
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326 
let 
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327 
fun mtch (instsp as (tyinsts,insts)) = fn 
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328 
(Var(ixn,T), t) => 
12784  329 
if loose_bvar(t,0) then raise MATCH 
16651  330 
else (case Envir.lookup' (insts, (ixn, T)) of 
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NONE => (typ_match thy (T, fastype_of t) tyinsts, 
17412  332 
Vartab.update_new (ixn, (T, t)) insts) 
15531  333 
 SOME u => if t aeconv u then instsp else raise MATCH) 
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334 
 (Free (a,T), Free (b,U)) => 
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if a=b then (typ_match thy (T,U) tyinsts, insts) else raise MATCH 
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336 
 (Const (a,T), Const (b,U)) => 
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337 
if a=b then (typ_match thy (T,U) tyinsts, insts) else raise MATCH 
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338 
 (Bound i, Bound j) => if i=j then instsp else raise MATCH 
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339 
 (Abs(_,T,t), Abs(_,U,u)) => 
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340 
mtch (typ_match thy (T,U) tyinsts, insts) (t,u) 
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341 
 (f$t, g$u) => mtch (mtch instsp (f,g)) (t, u) 
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342 
 (t, Abs(_,U,u)) => mtch instsp ((incr t)$(Bound 0), u) 
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343 
 _ => raise MATCH 
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344 
in fn tu => fn env => mtch env tu end; 
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345 

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346 

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347 
(* Matching of higherorder patterns *) 
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348 

15797  349 
fun match_bind(itms,binders,ixn,T,is,t) = 
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350 
let val js = loose_bnos t 
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351 
in if null is 
17412  352 
then if null js then Vartab.update_new (ixn, (T, t)) itms else raise MATCH 
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353 
else if js subset_int is 
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354 
then let val t' = if downto0(is,length binders  1) then t 
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355 
else mapbnd (idx is) t 
17412  356 
in Vartab.update_new (ixn, (T, mkabs (binders, is, t'))) itms end 
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357 
else raise MATCH 
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358 
end; 
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359 

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360 
fun match thy (po as (pat,obj)) envir = 
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361 
let 
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362 
(* Pre: pat and obj have same type *) 
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363 
fun mtch binders (pat,obj) (env as (iTs,itms)) = 
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364 
case pat of 
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365 
Abs(ns,Ts,ts) => 
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366 
(case obj of 
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367 
Abs(nt,Tt,tt) => mtch ((nt,Tt)::binders) (ts,tt) env 
15797  368 
 _ => let val Tt = Envir.typ_subst_TVars iTs Ts 
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369 
in mtch((ns,Tt)::binders) (ts,(incr obj)$Bound(0)) env end) 
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370 
 _ => (case obj of 
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371 
Abs(nt,Tt,tt) => 
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372 
mtch((nt,Tt)::binders) ((incr pat)$Bound(0),tt) env 
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373 
 _ => cases(binders,env,pat,obj)) 
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374 

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375 
and cases(binders,env as (iTs,itms),pat,obj) = 
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376 
let val (ph,pargs) = strip_comb pat 
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377 
fun rigrig1(iTs,oargs) = fold (mtch binders) (pargs~~oargs) (iTs,itms) 
16668  378 
fun rigrig2((a:string,Ta),(b,Tb),oargs) = 
379 
if a <> b then raise MATCH 

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380 
else rigrig1(typ_match thy (Ta,Tb) iTs, oargs) 
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381 
in case ph of 
15797  382 
Var(ixn,T) => 
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383 
let val is = ints_of pargs 
16651  384 
in case Envir.lookup' (itms, (ixn, T)) of 
15797  385 
NONE => (iTs,match_bind(itms,binders,ixn,T,is,obj)) 
15531  386 
 SOME u => if obj aeconv (red u is []) then env 
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387 
else raise MATCH 
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388 
end 
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389 
 _ => 
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390 
let val (oh,oargs) = strip_comb obj 
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391 
in case (ph,oh) of 
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392 
(Const c,Const d) => rigrig2(c,d,oargs) 
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393 
 (Free f,Free g) => rigrig2(f,g,oargs) 
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394 
 (Bound i,Bound j) => if i<>j then raise MATCH 
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395 
else rigrig1(iTs,oargs) 
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396 
 (Abs _, _) => raise Pattern 
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397 
 (_, Abs _) => raise Pattern 
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398 
 _ => raise MATCH 
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399 
end 
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400 
end; 
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401 

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402 
val pT = fastype_of pat 
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403 
and oT = fastype_of obj 
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404 
val envir' = apfst (typ_match thy (pT, oT)) envir; 
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405 
in mtch [] po envir' handle Pattern => first_order_match thy po envir' end; 
0  406 

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407 
fun matches thy po = (match thy po (Vartab.empty, Vartab.empty); true) handle MATCH => false; 
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408 

19880  409 
fun equiv thy (t, u) = matches thy (t, u) andalso matches thy (u, t); 
410 

0  411 

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412 
(* Does pat match a subterm of obj? *) 
22255  413 
fun matches_subterm thy (pat, obj) = 
414 
let 

415 
fun msub bounds obj = matches thy (pat, obj) orelse 

416 
(case obj of 

417 
Abs (x, T, t) => msub (bounds + 1) (snd (Term.dest_abs (Name.bound bounds, T, t))) 

418 
 t $ u => msub bounds t orelse msub bounds u 

419 
 _ => false) 

420 
in msub 0 obj end; 

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421 

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422 
fun first_order(Abs(_,_,t)) = first_order t 
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423 
 first_order(t $ u) = first_order t andalso first_order u andalso 
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424 
not(is_Var t) 
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425 
 first_order _ = true; 
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426 

20672  427 
fun pattern (Abs (_, _, t)) = pattern t 
428 
 pattern t = 

429 
let val (head, args) = strip_comb t in 

430 
if is_Var head then 

431 
forall is_Bound args andalso not (has_duplicates (op aconv) args) 

432 
else forall pattern args 

433 
end; 

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434 

12784  435 

436 
(* rewriting  simple but fast *) 

437 

17203  438 
fun rewrite_term thy rules procs tm = 
12784  439 
let 
13195  440 
val skel0 = Bound 0; 
441 

16939  442 
fun variant_absfree bounds (x, T, t) = 
12797  443 
let 
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444 
val (x', t') = Term.dest_abs (Name.bound bounds, T, t); 
16939  445 
fun abs u = Abs (x, T, abstract_over (Free (x', T), u)); 
446 
in (abs, t') end; 

12797  447 

12784  448 
fun match_rew tm (tm1, tm2) = 
18940  449 
let val rtm = the_default tm2 (Term.rename_abs tm1 tm tm2) in 
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tuned interfaces to support incremental match/unify (cf. versions in type.ML);
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450 
SOME (Envir.subst_vars (match thy (tm1, tm) (Vartab.empty, Vartab.empty)) rtm, rtm) 
16939  451 
handle MATCH => NONE 
13195  452 
end; 
12784  453 

15531  454 
fun rew (Abs (_, _, body) $ t) = SOME (subst_bound (t, body), skel0) 
13195  455 
 rew tm = (case get_first (match_rew tm) rules of 
15570  456 
NONE => Option.map (rpair skel0) (get_first (fn p => p tm) procs) 
13195  457 
 x => x); 
458 

16939  459 
fun rew1 bounds (Var _) _ = NONE 
460 
 rew1 bounds skel tm = (case rew2 bounds skel tm of 

15531  461 
SOME tm1 => (case rew tm1 of 
18940  462 
SOME (tm2, skel') => SOME (the_default tm2 (rew1 bounds skel' tm2)) 
15531  463 
 NONE => SOME tm1) 
464 
 NONE => (case rew tm of 

18940  465 
SOME (tm1, skel') => SOME (the_default tm1 (rew1 bounds skel' tm1)) 
15531  466 
 NONE => NONE)) 
12784  467 

16939  468 
and rew2 bounds skel (tm1 $ tm2) = (case tm1 of 
12784  469 
Abs (_, _, body) => 
470 
let val tm' = subst_bound (tm2, body) 

18940  471 
in SOME (the_default tm' (rew2 bounds skel0 tm')) end 
14787  472 
 _ => 
13195  473 
let val (skel1, skel2) = (case skel of 
474 
skel1 $ skel2 => (skel1, skel2) 

475 
 _ => (skel0, skel0)) 

16939  476 
in case rew1 bounds skel1 tm1 of 
477 
SOME tm1' => (case rew1 bounds skel2 tm2 of 

15531  478 
SOME tm2' => SOME (tm1' $ tm2') 
479 
 NONE => SOME (tm1' $ tm2)) 

16939  480 
 NONE => (case rew1 bounds skel2 tm2 of 
15531  481 
SOME tm2' => SOME (tm1 $ tm2') 
482 
 NONE => NONE) 

13195  483 
end) 
16939  484 
 rew2 bounds skel (Abs body) = 
13195  485 
let 
16939  486 
val (abs, tm') = variant_absfree bounds body; 
13195  487 
val skel' = (case skel of Abs (_, _, skel') => skel'  _ => skel0) 
16939  488 
in case rew1 (bounds + 1) skel' tm' of 
15531  489 
SOME tm'' => SOME (abs tm'') 
490 
 NONE => NONE 

12797  491 
end 
16939  492 
 rew2 _ _ _ = NONE; 
12784  493 

18940  494 
in the_default tm (rew1 0 skel0 tm) end; 
12784  495 

0  496 
end; 
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added failure trace information to pattern unification
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changeset

497 

a3d97348ceb6
added failure trace information to pattern unification
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changeset

498 
val trace_unify_fail = Pattern.trace_unify_fail; 