Implement 'as' operator.

tests/language/language.status

Index: tests/language/language.status
diff --git a/tests/language/language.status b/tests/language/language.status
index eea8c38553d0f04b71eff579eb4b1f46b90a25e1..7866f896fb72a4ee31c9a1454f2731a8d9d00dce 100644
--- a/tests/language/language.status
+++ b/tests/language/language.status
@@ -16,6 +16,7 @@
 # 3) Update the language/src directory with the updated test.
 
 [ $compiler == none ]
+cast_test: Fail # Issue 3400
 gc_test: Fail # Issue 1487
 field_override_test/none: Fail  # Issue 742: field shadowing now allowed
 field_override_test/01: Fail    # Issue 742: field shadowing now allowed
@@ -53,8 +54,8 @@ parameter_initializer6_negative_test: Fail # Issue 3502
 prefix_core_test: Fail # Issue 3638.
 
 # Issue 2501
-cascade_test: Pass,Fail  # Some cases pass, but for the wrong reason  
-cascade_precedence_test: Fail 
+cascade_test: Pass,Fail  # Some cases pass, but for the wrong reason
+cascade_precedence_test: Fail
 
 fauxverride_test/none: Fail # Issue 3778.
 
@@ -70,9 +71,10 @@ application_negative_test: Fail # Runtime only test, rewrite as multitest
 assert_keyword_negative_test: Fail # Runtime only test, rewrite as multitest
 assign_instance_method_negative_test: Fail  # Issue 3662
 body_less_constructor_wrong_arg_negative_test: Fail  # Runtime only test, rewrite as multitest
-call_operator_test: Pass # Issue 1355  
+call_operator_test: Pass # Issue 1355
 cascade_test: Pass,Fail # Issue 3729  Some cases pass, but for the wrong reason
 cascade_precedence_test: Fail  # Issue 3729
+cast_test: Fail  # Issue 3401
 char_escape_test: Pass # Issue 1654
 closure_call_wrong_argument_count_negative_test: Fail # Runtime only test, rewrite as multitest
 compile_time_constant_p_test/01: Fail # Issue 2580
@@ -85,7 +87,7 @@ default_factory_library_test: Fail          # Issue 514
 disable_privacy_test: Skip  # Issue 1882: Needs --disable_privacy support.
 duplicate_implements_test: Skip # Issue 976
 factory5_test/00: Fail # issue 3079
-field3a_negative_test: Fail # Issue 3655  
+field3a_negative_test: Fail # Issue 3655
 field_method4_negative_test: Fail  # Runtime only test, rewrite as multitest
 final_syntax_test/*: Skip  # can't handle base case
 instance_call_wrong_argument_count_negative_test: Fail # Runtime only test, rewrite as multitest
@@ -96,7 +98,7 @@ list_literal4_test: Fail       # Issue 1343
 map_literal4_test: Fail        # Issue 1343
 named_parameters_negative_test: Fail # Runtime only test, rewrite as multitest
 named_parameters_with_object_property_names_test: Fail # Issue 2137
-no_such_method_negative_test: Fail # Runtime only test, rewrite as multitest 
+no_such_method_negative_test: Fail # Runtime only test, rewrite as multitest
 override_field_test/04: Fail # Issue 3656
 private_member3_negative_test: Fail # Runtime only test?  rewrite as multitest
 pseudo_kw_illegal_test/08: Fail # Issue 356