problem 1 2 in scheme

1 files changed, 22 insertions, 0 deletions

diff --git a/scheme/utils.scm b/scheme/utils.scm
new file mode 100644
index 0000000..6ba98cd
--- /dev/null
+++ b/scheme/utils.scm
@@ -0,0 +1,22 @@
+(define fold
+  (lambda (f acc xs)
+    (if (null? xs)
+      acc
+      (fold f (f acc (car xs)) (cdr xs)))))
+
+(define sum
+  (lambda (xs) (fold + 0 xs)))
+
+(define range
+  (lambda (start stop step)
+    (if (>= start stop)
+      '()
+      (cons start (range (+ start step) stop step)))))
+
+(define filter
+  (lambda (predicate xs)
+    (if (null? xs)
+      '()
+      (let* ((x (car xs))
+             (filtered (filter predicate (cdr xs))))
+        (if (predicate x) (cons x filtered) filtered)))))