www.pudn.com > 12cocorc.zip > EXPR.ATG

$C   /* Generate Main Module */ 
COMPILER Expr 
/* This is a simple expression calculator */ 
 
/*----------------- Scanner Specifications ----------------------*/ 
 
CHARACTERS 
    letter = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz". 
    digit  = "0123456789". 
    tab    = CHR(9). 
    eol    = CHR(10). 
 
TOKENS 
    ident   =  letter {letter|digit}. 
    number  =  digit  { digit }. 
 
IGNORE eol+tab 
 
COMMENTS FROM "--" TO eol 
 
/*--------------------Parser Specification -------------------*/ 
 
PRODUCTIONS 
    Expr = StatSeq . 
 
    StatSeq = SYNC { Stat ";" SYNC} . 
 
    Stat =                          (. int value; .) 
       Expression<&value>           (. printf("%d\n", value); .) 
      . 
 
    Expression =       (. int result1, result2; .) 
       Term<&result1> 
       {   "+" Term<&result2>       (. result1 += result2; .) 
	 | "-" Term<&result2>       (. result1 -= result2; .) 
       }                            (. *result = result1; .) 
       . 
 
    Term =             (. int result1, result2; .) 
       Factor<&result1> 
       {   '*' Factor<&result2>     (. result1 *= result2; .) 
	 | '/' Factor<&result2>     (. result1 /= result2; .) 
       }                            (. *result = result1; .) 
       . 
 
    Factor =           (. int sign = 1; .) 
      [ "-"                         (. sign =- 1; .) 
      ] 
      (   Number 
	| "(" Expression ")" 
      )                            (. *result *= sign; .) 
      . 
 
   Number 
	=                          (. char buff[20]; .) 
	number                     (. S_GetString(S_Pos, S_Len, buff, sizeof(buff) - 1); 
				      *result = atoi(buff); .) 
	. 
 
/* 
   Ident 
	= 
	ident                      (. S_GetString(S_Pos, S_Len, name, 20); .) 
	. 
*/ 
 
END Expr.