New syntax proposal: Constructor Cascade (returns the cascadee) · Issue #172 · satyr/coco (original) (raw)

I've got a fair amount of code that looks like this:

head = document.createElement \head
style = document.createElement \style
  &id = \html5chan-style
  &textContent =
    '''
    %hakase.css%
    '''
head.appendChild style

title = document.createElement \title
  &textContent = board.title
head.appendChild title
html.appendChild head

or more purely, like this:

thing = new Thing
  &foo = 'bar'
  &baz = quux 'stuff'
something-with thing

where some of the code initializes and mutates an object just to pass it into another function (or return it). When available, I usually use a full constructor:

something-with new Thing foo: \bar baz: quux \stuff

But some constructors, e.g. DOM Image, have stupid arguments (no src), so an extra line of initialization is necessary.

I know I can use new with a block to create the new function() {...} form, but that doesn't work with Image, and it introduces overhead. Thus, my straw man is:

Constructor Cascade

Similar to cascade, but expression returns the original reference (after execution of the block) instead of the result of the last expression in the block.

fn = -> construct new Image
  &src = 'image.jpg'

document.body.appendChild do
  construct document.createElement \div
    &id = \stuff
    &classList.add \things
    &style
      &display = \block
    &textContent = 'are you a wizard'

=>

var img, x,x,x,y; img = function() { var $y = new Image $y.src = 'image.jpg' return $y }

$x = document.createElement('div') $x.id = 'stuff' $x.classList.add('things') y=y = y=x.style $y.display = 'block' $x.textContent = 'are you a wizard' document.body.appendChild($x)

Advantages

• Avoids needing an extra reference to a variable used only as an argument
• Cuts down on the verbosity of creating DOM trees, without any function calling overhead
• Avoids an extra return this at the end of a function, e.g. when using with new XMLHttpRequest
• Extends cascade to cover the other use of "fluent interface"-style chaining APIs, e.g: $(body).append($('<p>').text('just look at all this overhead!'))

Problems

• Couldn't think of a better symbol/keyword than construct
• Complicates the meaning of & even more
• Changes the order of code in the compiled js compared to the source