bux-lang/examples/macro_stmt_pat.bux

// Session 72 — macro fragment kinds `stmt` and `pat`
import Std::Io::{PrintLine};
import Std::String::{String_FromInt};
import Std::Test::{Test_AssertTrue, Test_Pass};

// stmt: splice a full statement (let / assign) into the template
macro! with_setup {
    ( $s:stmt, $body:expr ) => {
        {
            $s
            $body
        }
    }
}

// stmt from an expression-statement (assign)
macro! do_twice {
    ( $s:stmt ) => {
        {
            $s
            $s
            0
        }
    }
}

// pat: match arm pattern from call-site
macro! matches {
    ( $p:pat, $e:expr ) => {
        match $e {
            $p => 1,
            _ => 0
        }
    }
}

// Combined: extract payload when pattern matches
macro! if_let_like {
    ( $p:pat, $e:expr, $then:expr ) => {
        match $e {
            $p => $then,
            _ => -1
        }
    }
}

enum Opt {
    Some(int),
    None
}

func Main() -> int {
    // with_setup: inject `let x = 10` then use x
    let a: int = with_setup!(let x: int = 10, x + 1);
    Test_AssertTrue(a == 11);

    // do_twice: run assign twice
    var n: int = 0;
    discard do_twice!(n = n + 1);
    Test_AssertTrue(n == 2);

    // matches: literal / wildcard / enum (bind results — match-as-arg is fragile on buxc2)
    let m1: int = matches!(1, 1);
    let m2: int = matches!(2, 1);
    let m3: int = matches!(_, 99);
    Test_AssertTrue(m1 == 1);
    Test_AssertTrue(m2 == 0);
    Test_AssertTrue(m3 == 1);

    var o1: Opt = Opt { tag: Opt_Some };
    o1.data.Some_0 = 7;
    let o2: Opt = Opt { tag: Opt_None };
    let e1: int = if_let_like!(Opt::Some(v), o1, v);
    let e2: int = if_let_like!(Opt::Some(v), o2, v);
    let e3: int = matches!(Opt::None, o2);
    Test_AssertTrue(e1 == 7);
    Test_AssertTrue(e2 == -1);
    Test_AssertTrue(e3 == 1);

    PrintLine(String_FromInt(a));
    PrintLine(String_FromInt(n));
    Test_Pass("macro_stmt_pat");
    return 0;
}