bux-lang/examples/macro_hygiene.bux

// Session 66 — gensym hygiene + fragment kinds literal / block
import Std::Io::{PrintLine};
import Std::String::{String_FromInt};

// Template locals are gensym'd per expansion — two uses of `n` in one Main
// must not collide under the C backend's function-scoped locals.
macro! with_acc {
    ( $start:literal ) => {
        var n: int = $start;
        n = n + 1;
        n
    }
}

// literal: only int/float/string/char/bool literals (not 1+2)
macro! only_lit {
    ( $x:literal ) => {
        {
            $x
        }
    }
}

// block: only `{ … }` block expressions
macro! wrap_block {
    ( $b:block ) => {
        $b
    }
}

// lit alias for literal
macro! double_lit {
    ( $n:lit ) => {
        ($n) + ($n)
    }
}

func Main() -> int {
    // gensym: two expansions both introduce `n`
    let a: int = with_acc!(10);
    let b: int = with_acc!(20);
    // 11, 21
    let c: int = only_lit!(7);
    let d: int = wrap_block!({ 1 + 2 });
    let e: int = double_lit!(21);
    PrintLine(String_FromInt(a));
    PrintLine(String_FromInt(b));
    PrintLine(String_FromInt(c));
    PrintLine(String_FromInt(d));
    PrintLine(String_FromInt(e));
    if a != 11 {
        PrintLine("FAIL with_acc gensym a");
        return 1;
    }
    if b != 21 {
        PrintLine("FAIL with_acc gensym b");
        return 1;
    }
    if c != 7 {
        PrintLine("FAIL only_lit");
        return 1;
    }
    if d != 3 {
        PrintLine("FAIL wrap_block");
        return 1;
    }
    if e != 42 {
        PrintLine("FAIL double_lit");
        return 1;
    }
    PrintLine("PASS macro_hygiene");
    return 0;
}