Language front-end is almost the same as the one in a conventional compiler. It will perform syn tax and semantics checking on input language, constructing the intermediate representation of the source code.
The intermediate representation is a set of highly structured data items, recording the information in the source program, possible of being easily manipulated later in the front processor. The design and implementation of the language front-end may reference to PCRC project in NPAC: HPF front-end. (like a fig of front-end?)