sequences.extras: add a nullable span-slices word that allows f.

diff --git a/extra/sequences/extras/extras.factor b/extra/sequences/extras/extras.factor
index b057f6e4c208acaee5ceaf5a8ecc6bd28cf94b30..664100765a5dae381ef571783c98116635520634 100644 (file)
--- a/extra/sequences/extras/extras.factor
+++ b/extra/sequences/extras/extras.factor
@@ -207,6 +207,9 @@ ERROR: underlying-mismatch slice1 slice2 ;
     [ [ to>> ] bi@ max ]
     [ drop seq>> ] 2tri <slice> ;
 
+: ?span-slices ( slice1/f slice2/f -- slice )
+    2dup and [ span-slices ] [ or ] if ;
+
 :: rotate! ( seq n -- )
     seq length :> len
     n len mod dup 0 < [ len + ] when seq bounds-check drop 0 over