math.combinatorics: improve all-subsets and selections words.

basis/math/combinatorics/combinatorics-tests.factor

@@ -78,7 +78,7 @@ IN: math.combinatorics.tests
 
 [ { } ] [ { 1 2 } 0 selections ] unit-test
 
-[ { { 1 2 } } ] [ { 1 2 } 1 selections ] unit-test
+[ { { 1 } { 2 } } ] [ { 1 2 } 1 selections ] unit-test
 
 [ { { 1 1 } { 1 2 } { 2 1 } { 2 2 } } ]
 [ { 1 2 } 2 selections ] unit-test

basis/math/combinatorics/combinatorics.factor

@@ -1,8 +1,10 @@
 ! Copyright (c) 2007-2010 Slava Pestov, Doug Coleman, Aaron Schaefer, John Benediktsson.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: accessors assocs binary-search fry kernel locals math math.order
-    math.ranges namespaces sequences sorting make sequences.deep arrays
-    combinators ;
+
+USING: accessors arrays assocs binary-search fry kernel locals
+math math.order math.ranges namespaces sequences sequences.deep
+sorting ;
+
 IN: math.combinatorics
 
 <PRIVATE
@@ -129,21 +131,14 @@ PRIVATE>
     [ -rot ] dip each-combination ; inline
 
 : all-subsets ( seq -- subsets )
-    dup length [0,b] [
-        [ dupd all-combinations [ , ] each ] each
-    ] { } make nip ;
+    dup length [0,b] [ all-combinations ] with map concat ;
 
 : (selections) ( seq n -- selections )
-    dupd [ dup 1 > ] [
-        swap pick cartesian-product [
-            [ [ dup length 1 > [ flatten ] when , ] each ] each
-        ] { } make swap 1 -
-    ] while drop nip ;
+    [ [ 1array ] map dup ] [ 1 - ] bi*
+    [ cartesian-product concat ] with times
+    [ flatten ] map ;
 
 : selections ( seq n -- selections )
-    {
-        { 0 [ drop { } ] }
-        { 1 [ 1array ] }
-        [ (selections) ]
-    } case ;
+    dup 0 > [ (selections) ] [ 2drop { } ] if ;
+