From: John Benediktsson <mrjbq7@gmail.com>
Date: Sun, 21 Aug 2022 16:16:34 +0000 (-0700)
Subject: sequences.extras: adding nth-index
X-Git-Tag: 0.99~1120
X-Git-Url: https://gitweb.factorcode.org/gitweb.cgi?p=factor.git;a=commitdiff_plain;h=cdf7cce0463bea3ea406c7ef5bcac72991413326

sequences.extras: adding nth-index
---

diff --git a/extra/sequences/extras/extras-tests.factor b/extra/sequences/extras/extras-tests.factor
index 430e82ea33..53104befe7 100644
--- a/extra/sequences/extras/extras-tests.factor
+++ b/extra/sequences/extras/extras-tests.factor
@@ -322,4 +322,9 @@ math prettyprint sequences sequences.extras strings tools.test ;
 
 { { 5 11 26 61 } } [
     V{ 5 16 42 103 } [ - ] { } map-prior-as
-] unit-test
\ No newline at end of file
+] unit-test
+
+{ f } [ 0 CHAR: a "foo" nth-index ] unit-test
+{ 0 } [ 0 CHAR: a "abba" nth-index ] unit-test
+{ 3 } [ 1 CHAR: a "abba" nth-index ] unit-test
+{ f } [ 2 CHAR: a "abba" nth-index ] unit-test
diff --git a/extra/sequences/extras/extras.factor b/extra/sequences/extras/extras.factor
index f47ebc5650..027a3af199 100644
--- a/extra/sequences/extras/extras.factor
+++ b/extra/sequences/extras/extras.factor
@@ -823,3 +823,6 @@ M: virtual-zip-index nth-unsafe
     over [ seq>> nth-unsafe ] [ 2array ] bi* ; inline
 
 INSTANCE: virtual-zip-index immutable-sequence
+
+: nth-index ( n obj seq -- i )
+    [ = dup [ drop 1 - dup 0 < ] when ] with find drop nip ;