sequences.extras: make rotate support negative n.

extra/sequences/extras/extras-tests.factor

@@ -75,7 +75,7 @@ IN: sequences.extras.tests
 
 { "hello" "hello" } [ "hello" dup 0 rotate ] unit-test
 { "hello" "llohe" } [ "hello" dup 2 rotate ] unit-test
-[ "hello" dup -1 rotate ] must-fail
+{ "hello" "ohell" } [ "hello" dup -1 rotate ] unit-test
 
 { "hello" } [ "hello" dup 0 rotate! ] unit-test
 { "lohel" } [ "hello" dup 3 rotate! ] unit-test

extra/sequences/extras/extras.factor

@@ -196,7 +196,7 @@ ERROR: slices-don't-touch slice1 slice2 ;
     ] if ;
 
 : rotate ( seq n -- seq' )
-    cut prepend ;
+    dup 0 > [ cut ] [ abs cut* ] if prepend ;
 
 :: rotate! ( seq n -- )
     n seq bounds-check length :> end