fix(resolver): define variable on assignment

if a variable is not already defined when an assignment is visited, it is then defined in the current scope

midas/checker/resolver.py

@@ -13,7 +13,7 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
 
     def __init__(self):
         self.locals: dict[p.Expr, int] = {}
-        self.scopes: list[dict[str, bool]] = []
+        self.scopes: list[dict[str, bool]] = [{}]
 
     def resolve(self, *objects: p.Stmt | p.Expr) -> None:
         """Resolve the given statements or expressions"""
@@ -77,6 +77,12 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
                 self.locals[expr] = i
                 return
 
+    def is_defined(self, name: str) -> bool:
+        for scope in self.scopes:
+            if name in scope:
+                return True
+        return False
+
     def resolve_function(self, function: p.Function) -> None:
         """Resolve a function definition
 
@@ -111,7 +117,13 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
         self.resolve(stmt.value)
         for target in stmt.targets:
             match target:
-                case p.VariableExpr() | p.GetExpr():
+                case p.VariableExpr(name=name):
+                    if not self.is_defined(name):
+                        self.declare(name)
+                        self.define(name)
+                    target.accept(self)
+
+                case p.GetExpr():
                     target.accept(self)
                 case _:
                     raise Exception(f"Unsupported assignment to {target}")