futzing with condlike things.

hy/compiler.py

@@ -94,10 +94,15 @@ class HyASTCompiler(object):
     @builds("if")
     def compile_if_expression(self, expr):
         expr.pop(0)
+        test = self.compile(expr.pop(0))
+        body = self._code_branch(self.compile(expr.pop(0)))
+        orel = []
+        if len(expr) > 0:
+            orel = self._code_branch(self.compile(expr.pop(0)))
 
-        return ast.If(test=self.compile(expr.pop(0)),
-                      body=self._code_branch(self.compile(expr.pop(0))),
-                      orelse=self._code_branch(self.compile(expr.pop(0))),
+        return ast.If(test=test,
+                      body=body,
+                      orelse=orel,
                       lineno=expr.start_line,
                       col_offset=expr.start_column)
 

hy/core/bootstrap.py

@@ -28,3 +28,20 @@ from hy.models.symbol import HySymbol
 def defn_macro(tree):
     return HyExpression([HySymbol("def"),
                          tree[1], HyExpression([HySymbol("fn")] + tree[2:])])
+
+
+@macro("cond")
+def cond_macro(tree):
+    tree.pop(0)  # cond flag
+    it = iter(tree)
+    conds = iter(zip(it, it))
+    test, branch = next(conds)
+
+    root = HyExpression([HySymbol("if"), test, branch])
+    ret = root
+    for (test, branch) in conds:
+        n = HyExpression([HySymbol("if"), test, branch])
+        ret.append(n)
+        ret = n
+
+    return root