Moving `for' to a "macro"

hy/compiler.py

@@ -380,7 +380,7 @@ class HyASTCompiler(object):
             col_offset=expression.start_column,
             targets=[name], value=what)
 
-    @builds("for")
+    @builds("foreach")
     def compile_for_expression(self, expression):
         ret_status = self.returnable
         self.returnable = False

hy/core/bootstrap.py

@@ -22,6 +22,7 @@
 from hy.macros import macro
 from hy.models.expression import HyExpression
 from hy.models.symbol import HySymbol
+from hy.models.list import HyList
 
 
 @macro("defn")
@@ -47,6 +48,37 @@ def cond_macro(tree):
     return root
 
 
+@macro("for")
+def for_macro(tree):
+    tree.pop(0)
+    ret = None
+    # for [x iter y iter] ...
+    # ->
+    # foreach x iter
+    #   foreach y iter
+    #     ...
+
+    it = iter(tree.pop(0))
+    blocks = list(zip(it, it))  # List for Python 3.x degenerating.
+
+    key, val = blocks.pop(0)
+    ret = HyExpression([HySymbol("foreach"),
+                        HyList([key, val])])
+    root = ret
+    ret.replace(tree)
+
+    for key, val in blocks:
+        # x, [1, 2, 3,  4]
+        nret = HyExpression([HySymbol("foreach"),
+                             HyList([key, val])])
+        nret.replace(key)
+        ret.append(nret)
+        ret = nret
+
+    [ret.append(x) for x in tree]  # we really need ~@
+    return root
+
+
 @macro("_>")
 def threading_macro(tree):
     tree.pop(0)

hy/macros.py

@@ -37,6 +37,7 @@ def process(tree):
     if isinstance(tree, HyExpression):
         fn = tree[0]
         ntree = HyExpression([fn] + [process(x) for x in tree[1:]])
+        ntree.replace(tree)
 
         if isinstance(fn, HyString):
             if fn in _hy_macros: