callbacks.js

// map :: (A -> B) -> Continuable<A> -> Continuable<B>
function map(lambda) {
    return function duplex(source) {
        return function continuable(callback) {
            source(function (err, value) {
                callback(err, err ? null : lambda(value))
            })
        }
    }
}

var source = function continuable(cb) {
  cb(null, 42)
}

function sink(err, value) {
  console.log("(", err, ", ", value, ")")
}

map(function (x) { return x * 2 })(source)(sink)

monad.js

// map :: (A -> B) -> ContinuableStream<A> -> ContinuableStream<B>
function map(lambda) {
    return function duplex(source) {
        return return { read: return function read(cb) {
            source.read()(function (err, value) {
                cb(err, err ? null : lambda(value))
            })
        } }
    }
}

pull-stream.js

// map :: (A -> B) -> PullStream<A> -> PullStream<B>
function map(lambda) {
    return function duplex(source) {
        return function stream(abort, callback) {
            source(abort, function (err, value) {
                callback(err, err ? null : lambda(value))
            })
        }
    }
}