Fix if-let, add when-let

d-.scm

@@ -7,6 +7,7 @@
    as~>
    if-not
    if-let
+   when-let
    for
    partial
    argmin
@@ -39,14 +40,20 @@
      (let [(as v)]
        (as~> as (fn args ...) more ...))]))
 
-(define-syntax-rule (if-not pred body ...)
-  (if (not pred) body ...))
+(define-syntax-rule (if-not pred true-arm false-arm)
+  (if (not pred) true-arm false-arm))
 
-(define-syntax-rule (if-let ([ident test]) expr ...)
+(define-syntax-rule (if-let ([ident test]) true-arm false-arm)
+  (let ([t test])
+    (if t
+        (let ([ident t])
+          true-arm)
+        false-arm)))
+
+(define-syntax-rule (when-let ([ident test]) expr ...)
   (let ([ident test])
-    (if ident
-        (begin expr ...)
-        #f)))
+    (when ident
+      expr ...)))
 
 (define-syntax for
   (syntax-rules ()