Add 'Arbitrary' instance for records

[sharkdp]

This adds an Arbitrary instance for general records:

Example

type Person =
  { name :: { first :: String
            , last :: String
            }
  , age :: Int
  , height :: Number
  }

> persons ← randomSample' 10 (arbitrary :: Gen Person)

Note: This is the first time that I'm using the new (and awesome) typelevel-programming features of PureScript, so I'm not sure if I'm doing this correctly 😄

[LiamGoodacre]

Very cool 👍

[paf31]

This makes me think we should add ST support to purescript-records, so we can build the record in place.

[paf31]

That said, I'm not sure what type we'd give to in-place insertion of a new field :/

[paf31]

Thanks, looks great! I'll think a bit about the ST thing.

[paf31]

Here's something I put together for building records efficiently in place:

http://try.purescript.org/?backend=core&gist=27a137278caa203b3ebbd42f7386a0db

I might add this to purescript-records.