Use a subclassed tuple with methods instead of quotations

extra/astar/astar-docs.factor

@@ -3,7 +3,40 @@
 USING: help.markup help.syntax ;
 IN: astar
 
-{ find-path <astar> considered } related-words
+HELP: astar
+{ $description "This tuple must be subclassed and its method " { $link cost } ", "
+  { $link heuristic } ", and " { $link neighbours } " must be implemented. "
+  "Alternatively, the " { $link <astar> } " word can be used to build a non-specialized version." } ;
+
+HELP: cost
+{ $values
+  { "from" "a node" }
+  { "to" "a node" }
+  { "astar" "an instance of a subclassed " { $link astar } " tuple" }
+  { "n" "a number" }
+}
+{ $description "Return the cost to go from " { $snippet "from" } " to " { $snippet "to" } ". "
+  { $snippet "to" } " is necessarily a neighbour of " { $snippet "from" } "."
+} ;
+
+HELP: heuristic
+{ $values
+  { "from" "a node" }
+  { "to" "a node" }
+  { "astar" "an instance of a subclassed " { $link astar } " tuple" }
+  { "n" "a number" }
+}
+{ $description "Return the estimated (undervalued) cost to go from " { $snippet "from" } " to " { $snippet "to" } ". "
+  { $snippet "from" } " and " { $snippet "to" } " are not necessarily neighbours."
+} ;
+
+HELP: neighbours
+{ $values
+  { "node" "a node" }
+  { "astar" "an instance of a subclassed " { $link astar } " tuple" }
+  { "seq" "a sequence of nodes" }
+}
+{ $description "Return the list of nodes reachable from " { $snippet "node" } "." } ;
 
 HELP: <astar>
 { $values
@@ -16,7 +49,8 @@ HELP: <astar>
   { $snippet "neighbours" } " one builds the list of neighbours. The "
   { $snippet "cost" } " and " { $snippet "heuristic" } " ones represent "
   "respectively the cost for transitioning from a node to one of its neighbour, "
-  "and the underestimated cost for going from a node to the target."
+  "and the underestimated cost for going from a node to the target. This solution "
+  "may not be as efficient as subclassing the " { $link astar } " tuple."
 } ;
 
 HELP: find-path

extra/astar/astar.factor

@@ -5,44 +5,48 @@ IN: astar
 
 ! This implements the A* algorithm. See http://en.wikipedia.org/wiki/A*
 
+TUPLE: astar g in-closed-set ;
+GENERIC: cost ( from to astar -- n )
+GENERIC: heuristic ( from to astar -- n )
+GENERIC: neighbours ( node astar -- seq )
+
 <PRIVATE
 
-TUPLE: astar neighbours heuristic cost
-    goal g origin in-open-set in-closed-set open-set ;
+TUPLE: (astar) astar goal origin in-open-set open-set ;
 
 : (add-to-open-set) ( h node astar -- )
     2dup in-open-set>> at* [ over open-set>> heap-delete ] [ drop ] if
     [ swapd open-set>> heap-push* ] [ in-open-set>> set-at ] 2bi ;
 
 : add-to-open-set ( node astar -- )
-    [ g>> at ] 2keep
-    [ [ goal>> ] [ heuristic>> call( n1 n2 -- c ) ] bi + ] 2keep
+    [ astar>> g>> at ] 2keep
+    [ [ goal>> ] [ astar>> heuristic ] bi + ] 2keep
     (add-to-open-set) ;
 
 : ?add-to-open-set ( node astar -- )
-    2dup in-closed-set>> key? [ 2drop ] [ add-to-open-set ] if ;
+    2dup astar>> in-closed-set>> key? [ 2drop ] [ add-to-open-set ] if ;
 
 : move-to-closed-set ( node astar -- )
-    [ in-closed-set>> conjoin ] [ in-open-set>> delete-at ] 2bi ;
+    [ astar>> in-closed-set>> conjoin ] [ in-open-set>> delete-at ] 2bi ;
 
 : get-first ( astar -- node )
     [ open-set>> heap-pop drop dup ] [ move-to-closed-set ] bi ;
 
 : set-g ( origin g node astar -- )
-    [ [ origin>> set-at ] [ g>> set-at ] bi-curry bi-curry bi* ] [ ?add-to-open-set ] 2bi ;
+    [ [ origin>> set-at ] [ astar>> g>> set-at ] bi-curry bi-curry bi* ] [ ?add-to-open-set ] 2bi ;
 
 : cost-through ( origin node astar -- cost )
-    [ cost>> call( n1 n2 -- c ) ] [ nip g>> at ] 3bi + ;
+    [ astar>> cost ] [ nip astar>> g>> at ] 3bi + ;
 
 : ?set-g ( origin node astar -- )
     [ cost-through ] 3keep [ swap ] 2dip
-    3dup g>> at [ 1/0. ] unless* > [ 4drop ] [ set-g ] if ;
+    3dup astar>> g>> at [ 1/0. ] unless* > [ 4drop ] [ set-g ] if ;
 
 : build-path ( target astar -- path )
     [ over ] [ over [ [ origin>> at ] keep ] dip ] produce 2nip reverse ;
 
 : handle ( node astar -- )
-    dupd [ neighbours>> call( node -- neighbours ) ] keep [ ?set-g ] curry with each ;
+    dupd [ astar>> neighbours ] keep [ ?set-g ] curry with each ;
 
 : (find-path) ( astar -- path/f )
     dup open-set>> heap-empty? [
@@ -53,20 +57,25 @@ TUPLE: astar neighbours heuristic cost
 
 : (init) ( from to astar -- )
     swap >>goal
-    H{ } clone >>g
+    H{ } clone over astar>> (>>g)
+    H{ } clone over astar>> (>>in-closed-set)
     H{ } clone >>origin
     H{ } clone >>in-open-set
-    H{ } clone >>in-closed-set
     <min-heap> >>open-set
-    [ 0 ] 2dip [ (add-to-open-set) ] [ g>> set-at ] 3bi ;
+    [ 0 ] 2dip [ (add-to-open-set) ] [ astar>> g>> set-at ] 3bi ;
+
+TUPLE: astar-simple < astar cost heuristic neighbours ;
+M: astar-simple cost cost>> call( n1 n2 -- c ) ;
+M: astar-simple heuristic heuristic>> call( n1 n2 -- c ) ;
+M: astar-simple neighbours neighbours>> call( n -- neighbours ) ;
 
 PRIVATE>
 
 : find-path ( start target astar -- path/f )
-    [ (init) ] [ (find-path) ] bi ;
+    (astar) new [ (>>astar) ] keep [ (init) ] [ (find-path) ] bi ;
 
 : <astar> ( neighbours cost heuristic -- astar )
-    astar new swap >>heuristic swap >>cost swap >>neighbours ;
+    astar-simple new swap >>heuristic swap >>cost swap >>neighbours ;
 
 : considered ( astar -- considered )
     in-closed-set>> keys ;