iferr.coffee

iferr = (fail, succ) -> (err, a...) -> if err? then fail err else succ a...

# example
foo = (cb) ->
  fs.readFile something, iferr cb, (contents) ->
    # yey, no need to `return cb err if err?` all over the place

Javascript version:

function iferr(fail, succ) {
    return function(err, result) {
        if (err) {
            fail(err);
        } else {
            succ(result); // Multiple arguments would require some succ.apply magic
        }
    };
}

// Example
function foo(cb) {
    fs.readFile(something, iferr(cb, function(contents) {
        // No need to check for err here.
        // If there was one, it will be passed to cb and we won't be called.
    }));
}