Merge branch 'master' into pr/430

hy/core/macros.hy

@@ -45,10 +45,18 @@
 
   (if (empty? body)
     (macro-error None "`for' requires a body to evaluate"))
-  (if args
-    `(for* [~(.pop args 0) ~(.pop args 0)]
-       (for ~args ~@body))
-    `(do ~@body)))
+
+  (if (empty? args)
+    `(do ~@body)
+    (if (= (len args) 2)
+      ; basecase, let's just slip right in.
+      `(for* [~@args] ~@body)
+      ; otherwise, let's do some legit handling.
+      (let [[alist (slice args 0 nil 2)]
+            [ilist (slice args 1 nil 2)]]
+        `(do
+           (import itertools)
+           (for* [(, ~@alist) (itertools.product ~@ilist)] ~@body))))))
 
 
 (defmacro with [args &rest body]

tests/native_tests/language.hy

@@ -41,6 +41,46 @@
   (assert (= count 150)))
 
 
+(defn test-nasty-for-nesting []
+  "NATIVE: test nesting for loops harder"
+  ;; This test and feature is dedicated to @nedbat.
+
+  ;; let's ensure empty iterating is an implicit do
+  (setv t 0)
+  (for [] (setv t 1))
+  (assert (= t 1))
+
+  ;; OK. This first test will ensure that the else is hooked up to the
+  ;; for when we break out of it.
+  (for [x (range 2)
+        y (range 2)]
+      (break)
+    (else (throw Exception)))
+
+  ;; OK. This next test will ensure that the else is hooked up to the
+  ;; "inner" iteration
+  (for [x (range 2)
+        y (range 2)]
+    (if (= y 1) (break))
+    (else (throw Exception)))
+
+  ;; OK. This next test will ensure that the else is hooked up to the
+  ;; "outer" iteration
+  (for [x (range 2)
+        y (range 2)]
+    (if (= x 1) (break))
+    (else (throw Exception)))
+
+  ;; OK. This next test will ensure that we call the else branch exactly
+  ;; once.
+  (setv flag 0)
+  (for [x (range 2)
+        y (range 2)]
+    (+ 1 1)
+    (else (setv flag (+ flag 2))))
+  (assert (= flag 2)))
+
+
 (defn test-while-loop []
   "NATIVE: test while loops?"
   (setv count 5)