From acc561366f3fe6ec0377103f52ef0f7e923711c9 Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rhogenson@posteo.net>
Date: Mon, 1 Aug 2022 19:35:19 -0700
Subject: Modify the project structure.

Now the lib directory contains what will eventually end up on the
user's /usr/lib/csc. When I write make install, it will copy all of
the .csc files from lib into the destination lib directory. This means I
can start working on the standard library in lib/scheme.
---
 lib/csc/strings.csc | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 lib/csc/strings.csc

(limited to 'lib/csc/strings.csc')

diff --git a/lib/csc/strings.csc b/lib/csc/strings.csc
new file mode 100644
index 0000000..255a2fd
--- /dev/null
+++ b/lib/csc/strings.csc
@@ -0,0 +1,64 @@
+(define-library (csc strings)
+  (export
+    contains?
+    has-prefix?
+    index
+    join
+    split
+    str-quote)
+  (import (scheme base)
+          (only (scheme case-lambda) case-lambda)
+          (only (scheme write) write)
+          (only (csc list) intercalate)
+          (only (csc loop)
+            loop
+            return))
+  (begin
+
+
+    (define (has-prefix? str prefix)
+      (and (<= (string-length prefix) (string-length str))
+           (string=? prefix (substring str 0 (string-length prefix)))))
+
+
+    (define (str-quote s)
+      (let ((out (open-output-string)))
+        (write s out)
+        (get-output-string out)))
+
+
+    (define (index s substr)
+      (loop for i from 0
+            for s = s then (string-copy s 1)
+            until (string=? "" s)
+            if (has-prefix? s substr)
+              return i
+            finally (return -1)))
+
+
+    (define (contains? s substr)
+      (if (string=? "" substr)
+        #t
+        (not (negative? (index s substr)))))
+
+
+    (define (join sep strings)
+      (apply string-append (intercalate sep strings)))
+
+
+    (define split
+      (case-lambda
+        ((s sep n)
+          (if (= 0 n)
+            '()
+            (loop for n = n then (- n 1)
+                  for s = s then (string-copy s (+ i (string-length sep)))
+                  for i = (let ((i (index s sep)))
+                            (if (or (negative? i)
+                                    (= 1 n))
+                              (string-length s)
+                              i))
+                  collect (substring s 0 i)
+                  while (< i (string-length s)))))
+        ((s sep)
+          (split s sep -1))))))
-- 
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