CAP/TP02/ariteval/Arit.g4

grammar Arit;

// MIF08@Lyon1 and CAP@ENSL, arit evaluator

@header {
# header - mettre les déclarations globales
import sys
idTab = {};

class UnknownIdentifier(Exception):
    pass

class DivByZero(Exception):
    pass

def checkID(s):
  if s not in idTab:
    raise UnknownIdentifier(s)

def getID(s):
  try:
    return idTab[s]
  except IndexError:
    raise UnknownIdentifier(s)

}

prog: e0=expr EOF {print($e0.text, "=>", $e0.val)};

expr returns [int val]:
  | e=expr '+' t=term {$val = $e.val + $t.val}
  | t=term {$val = $t.val}
  ;

term returns [int val]:
  | t=term '*' f=fxpr {$val = $t.val * $f.val}
  | f=fxpr {$val = $f.val}
  ;

fxpr returns [int val]:
  | ID {$val = getID($ID.text)}
  | INT {$val = int($INT.text)}
  | '(' e=expr ')' {$val = $e.val}
  ;


COMMENT
 : '//' ~[\r\n]* -> skip
 ;

ID : ('a'..'z'|'A'..'Z')+;
INT: '0'..'9'+;
WS : [ \t\r\n]+ -> skip ; // skip spaces, tabs, newlines