{/*   FOUR FUNCTION CALCULATOR: FFCALC.SYN           */}

// -- CONFIGURATION SECTION ----------------------------
[
  default token type = double
  disregard white space
  lexeme { real}
]

// -- FOUR FUNCTION CALCULATOR -------------------------
(void) calculator $
 -> [calculation?, '\n']..., eof

(void) calculation
 -> expression:x                      =printf("%g\n",x);
 -> name:n, '=', expression:x                         ={
                  printf("%c = %g\n",n+'A',value[n]=x);}
 -> error

expression
 -> term
 -> expression:x, '+', term:t                     = x+t;
 -> expression:x, '-', term:t                     = x-t;

term
 -> factor
 -> term:t, '*', factor:f                         = t*f;
 -> term:t, '/', factor:f                         = t/f;

factor
 -> name:n                                   = value[n];
 -> real
 -> '(', expression:x, ')'                          = x;
 -> '-', factor:f                                  = -f;

// -- LEXICAL UNITS ------------------------------------
digit   = '0-9'
eof     = -1

(void) white space
 -> ' ' + '\t' + '\r' + '\f' + '\v'
 -> "/*", ~eof?..., "*/"

(int) name
 -> 'a-z' + 'A-Z':c                             = c-'A';

real
 -> integer part:i, '.', fraction part:f          = i+f;
 -> integer part, '.'?
 -> '.', fraction part:f                            = f;

integer part
 -> digit:d                                     = d-'0';
 -> integer part:x, digit:d              = 10*x + d-'0';

fraction part
 -> digit:d                                =(d-'0')/10.;
 -> digit:d, fraction part:f           =(d-'0' + f)/10.;

{ /* -- EMBEDDED C ---------------------------------- */
  double value[64];                      /* registers */
  int main(void) {
    ffcalc();
    return 0;
  }
} /* -- END OF EMBEDDED C ----------------------------*/