From 77583a881b03ce38c8065c40641489fe88b61eb2 Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rhogenson@posteo.net>
Date: Sun, 9 Jan 2022 22:55:59 -0800
Subject: Write the linker.

---
 list.csc | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

(limited to 'list.csc')

diff --git a/list.csc b/list.csc
index 799b070..f425146 100644
--- a/list.csc
+++ b/list.csc
@@ -1,5 +1,7 @@
 (define-library (csc list)
   (export
+    enumerate
+    filter
     intercalate
     revappend
     split-at
@@ -40,4 +42,23 @@
       (match l
         ('() '())
         ((_) l)
-        ((head . tail) (cons head (cons x (intercalate x tail))))))))
+        ((head . tail) (cons head (cons x (intercalate x tail))))))
+
+
+    (define (enumerate l)
+      (let loop ((i 0)
+                 (l l))
+        (match l
+          ('() '())
+          ((head . tail) (cons (cons i head) (loop (+ 1 i) tail))))))
+
+
+    (define (filter p l)
+      (let loop ((l l)
+                 (acc '()))
+        (match l
+          ('() (reverse acc))
+          ((x . xs)
+           (if (p x)
+             (loop xs (cons x acc))
+             (loop xs acc))))))))
-- 
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