I am a Mac user.
after edit the hdl file by the external editor i can not load the file. but before edit the file i could load the hdl file.
The most common cause is that your editor is saving the the edited file in UTF-8 encoding.
You need to set your editor to save in ASCII or ANSI encoding.
There is also a bug in your HDL. You might want to read the Hardware Construction Survival Guide
, specifically the HDL syntax and the meaning of "a=a"