parser.py

error = lambda t: pass # hipotetico
getToken = lambda: pass # hipotetico

token = getToken()

def eat(t):
    if token == t:
        token = getToken()
    else
        error()

EXPR,IF,FOR,OTHER,SEMICOLON,OPEN_BRACKET,CLOSE_BRACKET=(1,2,3,4,5,6) # definicao dos tokens para essa primeira gramitca

def stmt():
    if token == EXPR:
        eat(EXPR)
        eat(SEMICOLON)
    elif token == IF:
        eat(OPEN_BRACKET)
        eat(IF)
        eat(EXPR)
        eat(CLOSE_BRACKET)
        stmt()
    elif token == FOR:
        eat(FOR)
        eat(OPEN_BRACKET)
        optexpr()
        eat(SEMICOLON)
        optexpr()
        eat(SEMICOLON)
        optexpr()
        eat(CLOSE_BRACKET)
        stmt()
    elif token == OTHER:
        eat(OTHER)
    else:
        error()

def optexpr():
    if token == EXPR:
        eat(EXPR)