if-not and when-not

d-.scm

@@ -3,6 +3,8 @@
   #:export
   (~>
    ~>>
+   if-not
+   when-not
    partial
    argmin))
 
@@ -18,6 +20,12 @@
     [(_ v (fn args ...) more ...) (~> (fn args ... v) more ...)]
     [(_ v fn more ...) (~> (fn v) more ...)]))
 
+(define-syntax-rule (if-not pred body ...)
+  (if (not pred) body ...))
+
+(define-syntax-rule (when-not pred body ...)
+  (when (not pred) body ...))
+
 (define (partial fn . args)
   (lambda x (apply fn (append args x))))
 

test.scm

@@ -23,6 +23,15 @@
    (define value (~>> 1 (/ 2) (/ 2)))
    (assert (= value 1))))
 
+(define-test if-not
+  (assert (eq? (if-not #f 'a 'b) 'a)))
+
+(define-test when-not
+  (positive-case
+   (assert (eq? (when-not #f 'do-some-stuff 'return) 'return)))
+  (negative-case
+   (assert (unspecified? (when-not #t 'do-some-stuff 'return)))))
+
 (define-test partial
   (test
    (define value (partial / 2))