Contracts For CoffeeScript

#1

Post by swannodette » Tue, Aug 30, 2011, 12:03 AM UTC

Contracts For CoffeeScript
disnetdev.com

Re: Contracts For CoffeeScript

#2

Post by mobileman » Tue, Aug 30, 2011, 12:42 AM UTC

This is just static types

Re: Contracts For CoffeeScript

#3

Post by jashkenas » Tue, Aug 30, 2011, 12:44 AM UTC

mobileman wrote: post #2

This is just static types

Not quite.

    isEven = (x) -> 
      x % 2 is 0

    f :: (!isOdd) -> !isEven
    f = (x) -> ...

Re: Contracts For CoffeeScript

#4

Post by chucknthem » Tue, Aug 30, 2011, 12:47 AM UTC

mobileman wrote: post #2

This is just static types

No, if you read the article, contracts are enforced at runtime!

Re: Contracts For CoffeeScript

#5

Post by jvoorhis » Tue, Aug 30, 2011, 12:47 AM UTC

jashkenas wrote: post #3

mobileman wrote: post #2

This is just static types

Not quite. isEven = (x) -> x % 2 is 0 f :: (!isOdd) -> !isEven f = (x) -> ...

Not hardly. The runtime can detect that a function invocation violates a post-condition only after all of that function's side-effects have been run.

Re: Contracts For CoffeeScript

#6

Post by chucknthem » Tue, Aug 30, 2011, 12:52 AM UTC

This is great, it's like Google's compiler library[0] but with run-time checking! Coffee script is still very hard to debug, this should help avoid about 80% of the mistakes I normally make when coding.

[0] http://code.google.com/closure/compiler/

Re: Contracts For CoffeeScript

#7

Post by gfodor » Tue, Aug 30, 2011, 1:01 AM UTC

jvoorhis wrote: post #5

jashkenas wrote: post #3

Earlier quoted context omitted.

Not quite. isEven = (x) -> x % 2 is 0 f :: (!isOdd) -> !isEven f = (x) -> ...

Not hardly. The runtime can detect that a function invocation violates a post-condition only after all of that function's side-effects have been run.

What's your point?

Re: Contracts For CoffeeScript

#8

Post by swannodette » Tue, Aug 30, 2011, 1:14 AM UTC

Library author covers the relevant history here, http://disnetdev.com/blog/2011/08/23/Contracts.coffee-Contra...

This Lambda The Ultimate discussion on Benjamin C. Pierce's (Types And Programming Languages) talk Types Considered Harmful is also of interest - the gist being that contracts are useful because sometimes static types are just too damn hard - http://lambda-the-ultimate.org/node/2828

EDIT: Might as well link to Brendan Eich's talk Proxies Are Awesome!, http://www.slideshare.net/BrendanEich/metaprog-5303821. I haven't really been following the Proxy thing and they seem quite useful. It's nice to see them applied so powerfully here.

Re: Contracts For CoffeeScript

#9

Post by bilalhusain » Tue, Aug 30, 2011, 1:33 AM UTC

jashkenas wrote: post #3

mobileman wrote: post #2

This is just static types

Not quite. isEven = (x) -> x % 2 is 0 f :: (!isOdd) -> !isEven f = (x) -> ...

it doesn't conflict with the prototype operator?

Re: Contracts For CoffeeScript

#10

Post by jvoorhis » Tue, Aug 30, 2011, 1:38 AM UTC

gfodor wrote: post #7

jvoorhis wrote: post #5

Earlier quoted context omitted.

Not hardly. The runtime can detect that a function invocation violates a post-condition only after all of that function's side-effects have been run.

What's your point?

That while this looks like a good extension to CoffeeScript, it's unfortunate that Haskell's type syntax was appropriated when the relationship between contracts and types is tenuous at best.

There are good uses for static type checkers and design by contract, but neither one is a good substitute for the other.