[Haskell-cafe] In " returnIO x = IO $ \ s -> (# s, x #)" what are the # symbols?

[Tikhon Jelvis]

That's special syntax to make an unboxed tuple. See the manual section on
unboxed types[1].

[1]:
https://downloads.haskell.org/~ghc/7.6.3/docs/html/users_guide/primitives.html

On Mon, Jul 13, 2015 at 5:23 PM, Jeffrey Brown <jeffbrown.the at gmail.com>
wrote:

> That appears here:
> http://hackage.haskell.org/package/base-4.8.0.0/docs/src/GHC-Base.html#line-1057
>
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