FORTH parsers are ultra simple - get the next space-separated token, if it is a number, push it on the stack, otherwise it's a word - look it up in the dictionary and (if it exists there) execute it.

Even simpler is you go the colorforth route, part of the source code is "pre parsed" by the editor, a prefix byte is added to each word (which is shown as different colors), then a simple dispatch loop with that prefix as a sort of opcode.