fix bug: let, letrec should require unique binding names in the same let/letrec

Technologicat · Technologicat · commit 6706ba0e22ed · 2018-10-03T17:26:06.000+03:00
diff --git a/unpythonic/let.py b/unpythonic/let.py
@@ -246,6 +246,8 @@ def _let(mode, body, **bindings):
     # are then already bound when the wrappers are called.
     env = _envcls()
     for k, v in bindings.items():
+        if k in env:
+            raise AttributeError("Cannot rebind the same name '{}' in a {} initializer list".format(k, mode))
         if mode == "letrec" and callable(v):
             try:
                 if not arity_includes(v, 1):
diff --git a/unpythonic/lispylet.py b/unpythonic/lispylet.py
@@ -238,6 +238,8 @@ def _let(bindings, body, *, env=None, mode="let"):
         return env if body is None else body(env)
 
     (k, v), *more = bindings
+    if k in env:
+        raise AttributeError("Cannot rebind the same name '{}' in a {} initializer list".format(k, mode))
     if mode == "letrec" and callable(v):
         try:
             if not arity_includes(v, 1):
