Fix stack effects

Add take-while

extra/sequences/lib/lib-tests.factor

@@ -41,3 +41,4 @@ math.functions tools.test ;
 [ V{ } [ delete-random drop ] keep length ] unit-test-fails
 
 [ { 1 9 25 } ] [ { 1 3 5 6 } [ sq ] [ even? ] map-until ] unit-test
+[ { 2 4 } ] [ { 2 4 1 3 } [ even? ] take-while ] unit-test

extra/sequences/lib/lib.factor

@@ -63,10 +63,14 @@ IN: sequences.lib
 : delete-random ( seq -- value )
     [ length random ] keep [ nth ] 2keep delete-nth ;
 
-: (map-until) ( quot pred -- )
+: (map-until) ( quot pred -- quot )
     [ dup ] swap 3compose
     [ [ drop t ] [ , f ] if ] compose [ find 2drop ] curry ;
 
-: map-until ( seq quot pred -- )
-    #! Example: { 1 3 5 6 } [ sq ] [ even? ] map-until . -> { 1 9 25 }
+: map-until ( seq quot pred -- newseq )
     (map-until) { } make ;
+
+: take-while ( seq quot -- newseq )
+    [ not ] compose
+    [ find drop [ head-slice ] when* ] curry
+    [ dup ] swap compose keep like ;