pratt_cps.c

// Direct style

int paren_prefix(Ctx *c) {
    next(c); // LPAREN
    int x = binary(c, -1);
    expect(c, RPAREN);
    return x;
}

int binary(Ctx *c, int min_prec) {
    int x = c->tok.prefix(c);
    while (c->tok.prec > min_prec)
        x = c->tok.postfix(c, x);
    return x;
}

// Continuation passing style

typedef int (*Cont)(Ctx *c, int x);

int paren_prefix(Ctx *c, Cont k) {
    pushk(c, k);
    next(c); // LPAREN
    return binary(c, paren_prefix2, -1);
}

int paren_prefix2(Ctx *c, int x) {
    expect(c, RPAREN);
    Cont k = popk(c);
    return k(c, x);
}

int binary(Ctx *c, Cont k, int min_prec) {
    pushk(c, k);
    pushi(c, min_prec);
    return c->tok.prefix(c, binary2);
}

int binary2(Ctx *c, int x) {
    int min_prec = popi(c);
    if (c->tok.prec > min_prec) {
        pushi(c, min_prec);
        return c->tok.postfix(c, binary2, x);
    }
    Cont k = popk(c);
    return k(c, x);
}