X-Git-Url: https://gitweb.factorcode.org/gitweb.cgi?p=factor.git;a=blobdiff_plain;f=extra%2Fsequences%2Fextras%2Fextras.factor;h=f47ebc56508934065d8e4552fe9df11cd3efa84e;hp=fbe65dc2ee477ef1e8bcbed358451a3d777c3b9c;hb=458848d43c085d649c58f0fbb399c4b6608f892f;hpb=726a8b784b91bb5e5d1ee01af46a6b91cf0ff438

diff --git a/extra/sequences/extras/extras.factor b/extra/sequences/extras/extras.factor
index fbe65dc2ee..f47ebc5650 100644
--- a/extra/sequences/extras/extras.factor
+++ b/extra/sequences/extras/extras.factor
@@ -801,6 +801,18 @@ INSTANCE: step-slice virtual-sequence
         [ [ push ] curry compose 3nested-each ] keep
     ] keep like ; inline
 
+: each-prior ( ... seq quot: ( ... prior elt -- ... ) -- ... )
+    '[ [ swap @ ] keep ]
+    sequence-operator 0 -rot each-integer-from drop ; inline
+
+: map-prior-as ( ... seq quot: ( ... prior elt -- elt' ) exemplar -- seq' )
+    [
+        '[ [ swap @ ] keep swap ] length-operator 0 -rot
+    ] dip map-integers-as nip ; inline
+
+: map-prior ( ... seq quot: ( ... prior elt -- elt' ) -- seq' )
+    over map-prior-as ; inline
+
 TUPLE: virtual-zip-index seq ;
 
 C: <zip-index> virtual-zip-index