[Haskell-cafe] identity function

[Edward Amsden]

It does precisely what you'd think. It returns the value passed in.
It's mainly used in cases where a higher-order function expects a
function, but you don't want to modify anything. See for instance
http://www.haskell.org/ghc/docs/7.0-latest/html/libraries/base-4.3.0.0/Data-Maybe.html#v:maybe

If I want to extract a value from a Maybe, but I don't particularly
care to apply a function to it, I can write (for instance)

maybe 0 id ma

Where 'ma' is my maybe value. (There's a library function fromMaybe,
but this should illustrate the idea.)

On Mon, Dec 20, 2010 at 5:14 PM, A Smith <asmith9983 at gmail.com> wrote:
> I've been reviewing the library, and have come unstuck with the id function.
> What's its purpose and can someone give me an example of its practical use.
> --
> Andrew
>
>
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-- 
------
Edward Amsden
Undergraduate
Computer Science
Rochester Institute of Technology