[antlr-interest] recursive-descent Lisp example

[Terence Parr]

Howdy.  Henry Baker has a nice example:

(defun parse-int (&aux (s +1) d (n 0))
  (and
   (and (or (match #\+)
            (and (match #\-) (setq s -1))
            (and))
        (match-type digit d) (setq n (ctoi d))
        (not (do () ((not (and (match-type digit d)
                               (setq n (+ (* n 10) (ctoi d)))))))))
   (* s n)))

from

http://home.pipeline.com/~hbaker1/Prag-Parse.html

this parses signed integers and returns the integer.  I'm no Lisp  
expert but I'm pretty sure that since "the operations [], {} and $  
correspond to the Common Lisp control structures AND, OR, and DO", I  
could go from rule to Lisp defun rather easily.

Rules are just pure-functional functions that return attributes; we  
use methods instead in OO languages but Lisp is the king of this sort  
of stuff.  My paper on ST by the way is called "A Pure Functional  
Language for Generating Structured Text".  I harp on how the nature  
of code gen and enforcing model-view separation tightly brackets the  
solution to a pure functional language (with lazy eval)....that is ST :)

Ter