Pattern Matching but also Entire Result

[yfeldblum]

It would be nice to be able to specify both a name for the whole value and also the names for the parts of the value in the LHS (or in a formal parameter). Here's sample syntax:

myobj: { p1: { a: 1, b: 2 }, p2 : { c: 3, d: 4 } }
myp1@{x, y}: myobj.p1
# myp1 == { a: 1, b: 2 }, x == 1, y == 2

The @ is the character that Haskell uses for this feature. CoffeeScript should choose the syntax most appropriate for and integrated with the rest of CoffeeScript for this particular feature.

[zmthy]

Does this achieve what you're asking for?
{ a: x, b: y }: myp1: myobj.p1
This assigns myobj.p1 to myp1, then deconstructs it into x and y.

[yfeldblum]

That is nice too. It is not exactly what I had in mind, because it does not operate in a single assignment expression and because it would be difficult to work into the formal parameters.

[jashkenas]

I think that Tesco has a solid answer ... that a series of partial matches is a fine way to accomplish this without adding a new symbol to the current syntax. And because pattern-matching-in-parameters isn't happening for now (the sister-issue for this, #362), it's less necessary. Closing as a wontfix.

[mitar]

{ a: x, b: y }: myp1: myobj.p1 does not seem to compile on http://coffeescript.org/ anymore?

[lydell]

@mitar use { a: x, b: y } = myp1 = myobj.p1 :)