Haskell: What is the difference between $ (dollar) and $! (dollar exclamation point)

Posted by Jelle Fresen on Stack Overflow See other posts from Stack Overflow or by Jelle Fresen
Published on 2010-05-07T09:36:48Z Indexed on 2010/05/07 9:48 UTC
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Can anybody explain the difference in Haskell between the operators ($) and ($!) (dollar sign vs dollar sign exclamation point)?

I haven't seen the use of $! anywhere so far, but while browsing through the Haskell reference on www.zvon.org, I noticed its existence and that it has the exact same definition as $. When trying some simple statements in a Haskell interpreter (ghci), I couldn't find any difference, nor could I find any reference to the operator in the top listed tutorials when googling for haskell tutorial.

So, just out of curiosity, what is the difference, if at all?

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