add len to Ltup interp and type check

Author: jsiek

interp_Ltup.py

@@ -19,6 +19,9 @@ def interp_exp(self, e, env):
         t = self.interp_exp(tup, env)
         n = self.interp_exp(index, env)
         return t[n]
+      case Call(Name('len'), [tup]):
+        t = self.interp_exp(tup, env)
+        return len(t)
       case Allocate(length, typ):
         array = [None] * length
         return array

type_check_Ltup.py

@@ -26,6 +26,15 @@ def type_check_exp(self, e, env):
             return ts[index]
           case _:
             raise Exception('error: expected a tuple, not ' + repr(tup_ty))
+      case Call(Name('len'), [tup]):
+        tup_t = self.type_check_exp(tup, env)
+        match tup_t:
+          case TupleType(ts):
+            return int
+          case Bottom():
+            return Bottom()
+          case _:
+            raise Exception('error, expected a tuple, not ' + repr(tup_t))
       case _:
         return super().type_check_exp(e, env)