Add negative?, positive?, zero?, 1+ 1-.

* module/mes/scm.mes (negative?, positive?, zero?, 1+, 1-): New functions.

module/mes/scm.mes

@@ -157,6 +157,21 @@
 (define (odd? x)
   (= 1 (remainder x 2)))
 
+(define (negative? x)
+  (< x 0))
+
+(define (positive? x)
+  (> x 0))
+
+(define (zero? x)
+  (= x 0))
+
+(define (1+ x)
+  (+ x 1))
+
+(define (1- x)
+  (- x 1))
+
 (define (expt x y)
   (let loop ((s 1) (count y))
     (if (= 0 count) s