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 ()

test.scm

@@ -31,6 +31,21 @@
   (define-test "test"
     (assert-equal 'a (if-not #f 'a 'b))))
 
+(define-test-suite "if-let"
+  (define-test "positive case"
+    (assert-equal 2 (if-let ([v (or #f 1)]) (+ v 1) 3)))
+  (define-test "negative case"
+    (assert-equal 3 (if-let ([v (and #f 1)]) (+ v 1) 3)))
+  (define-test "variable not shadowed in false arm"
+    (define v 3)
+    (assert-equal 3 (if-let ([v #f]) (+ v 1) v))))
+
+(define-test-suite "when-let"
+  (define-test "positive case"
+    (assert-equal 2 (when-let ([v (or #f 1)]) (+ v 1))))
+  (define-test "negative case"
+    (assert-equal (when #f #t) (when-let ([v (and #f 1)]) (+ v 1)))))
+
 (define-test-suite "for"
   (define-test "permutation"
     (define value (for ([i (iota 2)]
@@ -38,12 +53,6 @@
                        (cons i j)))
     (assert-equal '((0 . 0) (0 . 1) (1 . 0) (1 . 1)) value)))
 
-(define-test-suite "if-let"
-  (define-test "positive-case"
-    (assert-equal 2 (if-let ([v (or #f 1)]) (+ v 1))))
-  (define-test "negative-case"
-    (assert-equal #f (if-let ([v (and #f 1)]) (+ v 1)))))
-
 (define-test-suite "partial"
   (define-test "test"
     (define value (partial / 2))