Drop types from fn, which is nontrivial & simplify do

src/python/flowmetal/syntax_analyzer.py

@@ -49,17 +49,20 @@ class ConstraintExpr(TypeLevelExpr, NamedTuple):
 class ValueLevelExpr(object):
     """A base class for value-level expressions."""
 
+
+class TriviallyTypedExpr(ValueLevelExpr):
+    """And some of those expressions have trivial types."""
     @property
     def type(self) -> TypeExpr:
         """The type of an expression."""
 
 
-class AscribeExpr(TypeLevelExpr):
+class AscribeExpr(TriviallyTypedExpr, NamedTuple):
     value: ValueLevelExpr
     type: TypeLevelExpr
 
 
-class ConstExpr(ValueLevelExpr, NamedTuple):
+class ConstExpr(TriviallyTypedExpr, NamedTuple):
     """Constant expressions. Keywords, strings, numbers, that sort of thing."""
 
     token: p.ConstTokenBase
@@ -114,42 +117,22 @@ class StringExpr(ConstExpr):
 class ListExpr(ValueLevelExpr, NamedTuple):
     elements: List[ValueLevelExpr]
 
-    # FIXME (arrdem 2020-07-18):
-    #  Probably typed? Not sure.
-
-    @property
-    def type(self) -> TypeExpr:
-        if self.elements:
-            return self.elements[-1].type
-
 
 ## 'real' AST nodes
 class DoExpr(ValueLevelExpr, NamedTuple):
     effect_exprs: List[ValueLevelExpr]
     ret_expr: ValueLevelExpr
 
-    @property
-    def type(self) -> TypeExpr:
-        return self.ret_expr.type
-
 
 class LetExpr(ValueLevelExpr, NamedTuple):
     binding_exprs: List[Tuple]
     ret_expr: DoExpr
 
-    @property
-    def type(self) -> TypeExpr:
-        return self.ret_expr.type
-
 
 class FnExpr(ValueLevelExpr, NamedTuple):
     arguments: List
-    ret_expr: DoExpr
     ret_type: TypeExpr
-
-    @property
-    def type(self) -> TypeExpr:
-        return self.ret_type
+    ret_expr: DoExpr
 
 
 ## Reader implementation
@@ -310,7 +293,10 @@ class Analyzer(AnalyzerBase):
     def analyze_do(cls, do_token):
         tokens = cls._nows(do_token.data[1:])
         exprs = cls._terms(tokens)
-        return DoExpr(exprs[:-1], exprs[-1])
+        if exprs[:-1]:
+            return DoExpr(exprs[:-1], exprs[-1])
+        else:
+            return exprs[-1]
 
     @classmethod
     def analyze_fn(cls, fn_token):
@@ -334,7 +320,7 @@ class Analyzer(AnalyzerBase):
         # FIXME (arrdem 2020-07-18):
         #   This needs to happen with bindings
         body = cls.analyze(cls._do(fn_token, tokens))
-        return FnExpr(args, body, ascription or body.type)
+        return FnExpr(args, ascription, body)
 
 
 ## Analysis interface