1 files changed, 37 insertions, 1 deletions

@@ -7,9 +7,12 @@
 
   (export identity
           o
+          constantly
           assoc-ref
           slurp
-          eval/q)
+          eval/q
+          intersperse
+          string-intersperse)
 
   (begin
     (define (identity x) x)
@@ -24,6 +27,9 @@
                   h
                   (lambda (x) (h ((loop t) x))))))))
 
+    (define (constantly x)
+      (lambda _ x))
+
     (define assoc-ref
       (case-lambda
         ((key alist)
@@ -47,4 +53,34 @@
     (define (eval/q form env)           ; this is probably a bad idea
       (eval (list 'quasiquote form) env))
 
+    (define (intersperse xs delim)
+      (if (null? xs)
+          '()
+          (let loop ((acc (list (car xs)))
+                     (rest (cdr xs)))
+            (if (null? rest)
+                (reverse acc)
+                (loop (cons (car rest) (cons delim acc))
+                      (cdr rest))))))
+
+    (define (string-intersperse ss delim)
+      (apply string-append (intersperse ss delim)))
+
+    (define index
+      (case-lambda
+        ((xs needle)
+         (index xs needle eq? (constantly #f)))
+        ((xs needle comparator)
+         (index xs needle comparator (constantly #f)))
+        ((xs needle comparator fail)
+         (let loop ((i 0)
+                    (xs xs))
+           (cond
+            ((null? xs) (fail))
+            ((comparator (car xs) needle) i)
+            (else (loop (+ i 1) (cdr xs))))))))
+
+    (define (string-index str ch)
+      (index (string->list str) ch))
+
     ))