introduce modulus arithmetic to std lisp

1 files changed, 12 insertions, 6 deletions

diff --git a/src/lisp/std.lisp b/src/lisp/std.lisp
index 2a042a0..6c5beed 100644
--- a/src/lisp/std.lisp
+++ b/src/lisp/std.lisp
@@ -9,6 +9,18 @@
 (define (cdddddr ls) (cdr (cddddr ls)))
 
 (define (null? ls) (eq? ls '()))
+(define (zero? x) (eq? x 0))
+
+(define (remainder x y)
+  (if (> y x)
+      x
+      (remainder (- x y) y)))
+
+(define (quotient x y)
+  (/ x y))
+
+(define (even? x) (zero? (remainder x 2)))
+(define (odd? x) (not (even? x)))
 
 (define (length ls)
   (if (null? ls)
@@ -45,9 +57,3 @@
 
 (define (sum ls) (fold 0 + ls))
 (define (product ls) (fold 1 * ls))
-
-(define (enumerate start stop step)
-  (if (>= start stop)
-      '()
-      (cons start
-            (enumerate (+ start step) stop step))))