ATN in Lisp [file atn.lsp]

• A global variable *sent* points to a list of words that is the remaining input sentence:
  (GOOD CHINESE RESTAURANT IN LOS ALTOS)

• A global variable *word* points to the current word: GOOD

• (cat category ) tests whether a word is in the specified category. It can also translate the word, e.g. (cat 'month) might return 3 if *word* is MARCH.

• (next) moves to the next word in the input

• (saveptr) saves the current sentence position on a stack.

• (success) pops a saved position off the stack and returns T.

• (fail) restores a saved position from the stack (restoring *sent* and *word*) and returns NIL.