bullet-proof against UnknownArity

Technologicat · Technologicat · commit ba543628d2e8 · 2018-08-29T01:28:38.000+03:00
diff --git a/unpythonic/let.py b/unpythonic/let.py
@@ -249,17 +249,23 @@ def _let(mode, body, **bindings):
     env = _envcls()
     for k, v in bindings.items():
         if mode == "letrec" and callable(v):
-            if not arity_includes(v, 1):
-                raise ValueError("Arity mismatch; callable value must allow arity 1, to take in the environment.")
+            try:
+                if not arity_includes(v, 1):
+                    raise ValueError("Arity mismatch; callable value must allow arity 1, to take in the environment.")
+            except UnknownArity:  # well, we tried!
+                pass
             v = v(env)
         env[k] = v
     # decorators need just the final env; else run body now
     env.finalize()
     if body:
         if not callable(body):
             raise TypeError("Expected callable body, got '{}' with value '{}'".format(type(body), body))
-        if not arity_includes(body, 1):
-            raise ValueError("Arity mismatch; body must allow arity 1, to take in the environment.")
+        try:
+            if not arity_includes(body, 1):
+                raise ValueError("Arity mismatch; body must allow arity 1, to take in the environment.")
+        except UnknownArity:  # well, we tried!
+            pass
     return env if body is None else body(env)
 
 # decorator factory: almost as fun as macros?
diff --git a/unpythonic/lispylet.py b/unpythonic/lispylet.py
@@ -231,15 +231,21 @@ def _let(bindings, body, *, env=None, mode="let"):
         if body:
             if not callable(body):
                 raise TypeError("Expected callable body, got '{}' with value '{}'".format(type(body), body))
-            if not arity_includes(body, 1):
-                raise ValueError("Arity mismatch; body must allow arity 1, to take in the environment.")
+            try:
+                if not arity_includes(body, 1):
+                    raise ValueError("Arity mismatch; body must allow arity 1, to take in the environment.")
+            except UnknownArity:  # well, we tried!
+                pass
         # decorators need just the final env; else run body now
         return env if body is None else body(env)
 
     (k, v), *more = bindings
     if mode == "letrec" and callable(v):
-        if not arity_includes(v, 1):
-            raise ValueError("Arity mismatch; callable value must allow arity 1, to take in the environment.")
+        try:
+            if not arity_includes(v, 1):
+                raise ValueError("Arity mismatch; callable value must allow arity 1, to take in the environment.")
+        except UnknownArity:  # well, we tried!
+            pass
         v = v(env)
     env[k] = v
     return _let(more, body, env=env, mode=mode)  # FP loop (without TCO)
diff --git a/unpythonic/seq.py b/unpythonic/seq.py
@@ -10,7 +10,7 @@
 from unpythonic.env import env
 
 # evil inspect dependency, used only to provide informative error messages.
-from unpythonic.arity import arity_includes
+from unpythonic.arity import arity_includes, UnknownArity
 
 # sequence side effects in a lambda
 def begin(*vals):
@@ -310,8 +310,11 @@ def do(*items):
     e = env()
     def maybe_call(v):
         if callable(v):
-            if not arity_includes(v, 1):
-                raise ValueError("Arity mismatch; callable value must allow arity 1, to take in the environment.")
+            try:
+                if not arity_includes(v, 1):
+                    raise ValueError("Arity mismatch; callable value must allow arity 1, to take in the environment.")
+            except UnknownArity:  # well, we tried!
+                pass
             return v(e)
         else:
             return v
