# HG changeset patch
# User clasohm
# Date 778935868 -7200
# Node ID 91d5ac5ebb1739ebeeb3ca95d47652eadf53f1a3
# Parent  3ba470399605819444e636dac4139cdde24c07fa
moved from Contrib

diff -r 3ba470399605 -r 91d5ac5ebb17 src/Provers/astar.ML
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Provers/astar.ML	Wed Sep 07 13:04:28 1994 +0200
@@ -0,0 +1,59 @@
+(*  Title: 	astar
+    ID:         $Id$
+    Author: 	Norbert Voelker, FernUniversitaet Hagen
+    Remarks:    Implementation of A*-like proof procedure by modification
+		of the existing code for BEST_FIRST and best_tac so that the 
+		current level of search is taken into account.
+*)		
+		
+(*Insertion into priority queue of states, marked with level *)
+fun insert_with_level (lnth: int*int*thm, []) = [lnth]
+  | insert_with_level ((l,m,th), (l',n,th')::nths) = 
+      if  n<m then (l',n,th') :: insert_with_level ((l,m,th), nths)
+      else if  n=m andalso eq_thm(th,th')
+              then (l',n,th')::nths
+              else (l,m,th)::(l',n,th')::nths;
+
+(*For creating output sequence*)
+fun some_of_list []     = None
+  | some_of_list (x::l) = Some (x, Sequence.seqof (fn () => some_of_list l));
+
+infix THEN_ASTAR;
+val trace_ASTAR = ref false; 
+
+fun (Tactic tf0) THEN_ASTAR (satp, costf, tac) = 
+  let val tf = tracify trace_ASTAR tac;   
+      fun bfs (news,nprfs,level) =
+      let fun cost thm = (level,costf level thm,thm)
+      in (case  partition satp news  of
+            ([],nonsats) 
+		 => next (foldr insert_with_level (map cost nonsats, nprfs))
+          | (sats,_)  => some_of_list sats)
+      end and    
+      next []  = None
+        | next ((level,n,prf)::nprfs)  =
+            (if !trace_ASTAR 
+               then writeln("level = " ^ string_of_int level ^
+			 "  cost = " ^ string_of_int n ^ 
+                         "  queue length =" ^ string_of_int (length nprfs))  
+               else ();
+             bfs (Sequence.list_of_s (tf prf), nprfs,level+1))
+      fun tf st = bfs (Sequence.list_of_s (tf0 st), [], 0)
+  in traced_tac tf end;
+
+(*Ordinary ASTAR, with no initial tactic*)
+fun ASTAR (satp,costf) tac = all_tac THEN_ASTAR (satp,costf,tac);
+
+(* ASTAR with weight weight_ASTAR as a classical prover *) 
+val weight_ASTAR = ref 5; 
+
+fun astar_tac cs = 
+  SELECT_GOAL ( ASTAR (has_fewer_prems 1
+	      , fn level =>(fn thm =>size_of_thm thm + !weight_ASTAR *level)) 
+	      (step_tac cs 1));
+
+fun slow_astar_tac cs = 
+  SELECT_GOAL ( ASTAR (has_fewer_prems 1
+	      , fn level =>(fn thm =>size_of_thm thm + !weight_ASTAR *level)) 
+	      (slow_step_tac cs 1));
+