info bigloo

12.6 A simple example

Here is the code for a simple calculator implemented by an Lalr(1) grammar:

(begin
  (read/lalrp
   (lalr-grammar
    (nl plus mult minus div const lpar rpar)
    (lines
     (())
     ((lines expression nl)    (display "--> ") 
                               (display expression) 
                               (newline))
     ((lines nl)))
    (expression
     ((expression plus term)   (+ expression term))
     ((expression minus term)  (- expression term))
     ((term)                   term))
    (term
     ((term mult factor)       (* term factor))
     ((term div factor)        (/ term factor))
     ((factor)                 factor))
    (factor
     ((lpar expression rpar)   expression)
     ((const)                  const)))

   (regular-grammar ()
    ((+ (or #\tab #\space)) (ignore))
    (#\newline              'nl)
    ((+ digit)              (cons 'const (string->number (the-string))))
    (#\+                    'plus)
    (#\-                    'minus)
    (#\*                    'mult)
    (#\/                    'div)
    (#\(                    'lpar)
    (#\)                    'rpar))

   (current-input-port))
  (reset-eof (current-input-port)))

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