feat(checker): type check slice expressions

midas/checker/builtins.py

@@ -29,6 +29,7 @@ def define_builtins(reg: TypesRegistry):
     int = reg.define_type("int", BaseType(name="int"))
     float = reg.define_type("float", BaseType(name="float"))
     str = reg.define_type("str", BaseType(name="str"))
+    slice = reg.define_type("slice", BaseType(name="slice"))
 
     list = reg.define_type(
         "list",

midas/checker/python.py

@@ -507,6 +507,9 @@ class PythonTyper(
             expr.location, operation, [(expr.index, index)], {}
         )
 
+    def visit_slice_expr(self, expr: p.SliceExpr) -> Type:
+        return self.types.get_type("slice")
+
     def visit_base_type(self, node: p.BaseType) -> Type:
         base: Type
         try:

midas/checker/resolver.py

@@ -200,3 +200,11 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
     def visit_subscript_expr(self, expr: p.SubscriptExpr) -> None:
         self.resolve(expr.object)
         self.resolve(expr.index)
+
+    def visit_slice_expr(self, expr: p.SliceExpr) -> None:
+        if expr.lower is not None:
+            self.resolve(expr.lower)
+        if expr.upper is not None:
+            self.resolve(expr.upper)
+        if expr.step is not None:
+            self.resolve(expr.step)