More grammar to ast implementation

Author: ncw

ast/dump_test.go

@@ -19,6 +19,7 @@ func TestDump(t *testing.T){
 `BinOp(Left=Str(S="one"),Op=Add,Right=Str(S="two"))`},
 {&Module{}, `Module(Body=[])`},
 {&Module{Body: []Stmt{&Pass{}}}, `Module(Body=[Pass()])`},
+{&Module{Body: []Stmt{&ExprStmt{Value: &Tuple{}}}}, `Module(Body=[ExprStmt(Value=Tuple(Elts=[],Ctx=UnknownExprContext(0)))])`},
  }{
 out:=Dump(test.in)
 ifout!=test.out{