haste-compiler-0.5.3: lib/MVar.js

// MVar implementation.
// Since Haste isn't concurrent, takeMVar and putMVar don't block on empty
// and full MVars respectively, but terminate the program since they would
// otherwise be blocking forever.

function newMVar() {
    return ({empty: true});
}

function tryTakeMVar(mv) {
    if(mv.empty) {
        return {_:0, a:0, b:undefined};
    } else {
        var val = mv.x;
        mv.empty = true;
        mv.x = null;
        return {_:0, a:1, b:val};
    }
}

function takeMVar(mv) {
    if(mv.empty) {
        // TODO: real BlockedOnDeadMVar exception, perhaps?
        err("Attempted to take empty MVar!");
    }
    var val = mv.x;
    mv.empty = true;
    mv.x = null;
    return val;
}

function putMVar(mv, val) {
    if(!mv.empty) {
        // TODO: real BlockedOnDeadMVar exception, perhaps?
        err("Attempted to put full MVar!");
    }
    mv.empty = false;
    mv.x = val;
}

function tryPutMVar(mv, val) {
    if(!mv.empty) {
        return 0;
    } else {
        mv.empty = false;
        mv.x = val;
        return 1;
    }
}

function sameMVar(a, b) {
    return (a == b);
}

function isEmptyMVar(mv) {
    return mv.empty ? 1 : 0;
}