New benchmark

extra/benchmark/backtrack/backtrack.factor

@@ -0,0 +1,65 @@
+! Copyright (C) 2008 Slava Pestov.
+! See http://factorcode.org/license.txt for BSD license.
+USING: backtrack shuffle math math.ranges quotations locals fry
+kernel words io memoize macros io prettyprint sequences assocs
+combinators namespaces ;
+IN: benchmark.backtrack
+
+! This was suggested by Dr_Ford. Compute the number of quadruples
+! (a,b,c,d) with 1 <= a,b,c,d <= 10 such that we can make 24 by
+! placing them on the stack, and applying the operations
+! +, -, * and rot as many times as we wish.
+
+: nop ;
+
+MACRO: amb-execute ( seq -- quot )
+    [ length ] [ <enum> [ 1quotation ] assoc-map ] bi
+    '[ , amb , case ] ;
+
+: if-amb ( true false -- )
+    [
+        [ { t f } amb ]
+        [ '[ @ require t ] ]
+        [ '[ @ f ] ]
+        tri* if
+    ] with-scope ; inline
+
+: do-something ( a b -- c )
+    { + - * } amb-execute ;
+
+: some-rots ( a b c -- a b c )
+    #! Try to rot 0, 1 or 2 times.
+    { nop rot -rot } amb-execute ;
+
+MEMO: 24-from-1 ( a -- ? )
+    24 = ;
+
+MEMO: 24-from-2 ( a b -- ? )
+    [ do-something 24-from-1 ] [ 2drop ] if-amb ;
+
+MEMO: 24-from-3 ( a b c -- ? )
+    [ some-rots do-something 24-from-2 ] [ 3drop ] if-amb ;
+
+MEMO: 24-from-4 ( a b c d -- ? )
+    [ some-rots do-something 24-from-3 ] [ 4drop ] if-amb ;
+
+: find-impossible-24 ( -- n )
+    1 10 [a,b] [| a |
+        1 10 [a,b] [| b |
+            1 10 [a,b] [| c |
+                1 10 [a,b] [| d |
+                    a b c d 24-from-4
+                ] count
+            ] sigma
+        ] sigma
+    ] sigma ;
+
+: words { 24-from-1 24-from-2 24-from-3 24-from-4 } ;
+
+: backtrack-benchmark ( -- )
+    words [ reset-memoized ] each
+    find-impossible-24 pprint "/10000 quadruples can make 24." print
+    words [
+        dup pprint " tested " write "memoize" word-prop assoc-size pprint
+        " possibilities" print
+    ] each ;