Merge pull request #404 from github/none-is-the-loneliest-umber

Compile Python None expressions.

semantic-python/src/Language/Python/Core.hs

@@ -341,7 +341,11 @@ instance Compile Py.Module where
     in fmap (locate it) . foldr compile buildRecord stmts
 
 instance Compile Py.NamedExpression
-instance Compile Py.None
+
+instance Compile Py.None where
+  -- None is not overridable, and thus always points to the prelude's None.
+  compile _it cc _ = cc (pure "__semantic_prelude" ... "None")
+
 instance Compile Py.NonlocalStatement
 instance Compile Py.NotOperator
 

semantic-python/src/Prelude.score

@@ -10,8 +10,16 @@
 
   str <- type "str" object #record { __new__: \prim -> instance #unit prim #record{} };
 
+  NoneType <- type "None" object #record { __new__: \prim -> instance #unit prim #record{} };
+  None <- NoneType.__slots.__new__ #unit;
+
   getitem <- \super -> \item -> \attr ->
     if item.slots.?attr then item.slots.attr else #unit;
 
-  #record { type: type, object: object, str: str, getitem: getitem}
+  #record { type: type
+          , object: object
+          , str: str
+          , NoneType: NoneType
+          , None: None
+          , getitem: getitem}
 }

semantic-python/test/fixtures/4-02-nonetype.py

@@ -0,0 +1,2 @@
+# CHECK-TREE: { x <- __semantic_prelude.None; #record { x : x }}
+x = None