From 49e0ce47d4fdd3f41dde1e376977d545fc8c542e Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rhogenson@posteo.net>
Date: Sun, 7 Aug 2022 15:54:30 -0700
Subject: Define last-index.

---
 lib/csc/strings-test.csc | 18 ++++++++++++++++++
 lib/csc/strings.csc      |  8 ++++++++
 2 files changed, 26 insertions(+)

(limited to 'lib/csc')

diff --git a/lib/csc/strings-test.csc b/lib/csc/strings-test.csc
index 1f981ad..95dbb59 100644
--- a/lib/csc/strings-test.csc
+++ b/lib/csc/strings-test.csc
@@ -42,6 +42,24 @@
         (index "def" "a")))
 
 
+    (test last-index-last
+      (assert-equal
+        4
+        (last-index "ababa" "a")))
+
+
+    (test last-index-penultimate
+      (assert-equal
+        4
+        (last-index "ababab" "a")))
+
+
+    (test last-index-notfound
+      (assert-equal
+        -1
+        (last-index "abcdfads" ";")))
+
+
     (test contains
       (assert-equal
         #t
diff --git a/lib/csc/strings.csc b/lib/csc/strings.csc
index 255a2fd..373f9be 100644
--- a/lib/csc/strings.csc
+++ b/lib/csc/strings.csc
@@ -4,6 +4,7 @@
     has-prefix?
     index
     join
+    last-index
     split
     str-quote)
   (import (scheme base)
@@ -36,6 +37,13 @@
             finally (return -1)))
 
 
+    (define (last-index s substr)
+      (loop for i downfrom (- (string-length s) (string-length substr)) to 0
+            if (has-prefix? (string-copy s i) substr)
+              return i
+            finally (return -1)))
+
+
     (define (contains? s substr)
       (if (string=? "" substr)
         #t
-- 
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