From: Ivan Lazar Miljenovic <ivan.miljenovic@gmail.com>
Subject: Re: [Haskell-cafe] Constructor question
To: "michael rice" <nowgate@yahoo.com>
Cc: haskell-cafe@haskell.org
Date: Saturday, July 31, 2010, 9:32 AM

michael rice <nowgate@yahoo.com> writes:

> From: Data.Complex
>
> data (RealFloat a) => Complex a
>   = !a :+ !a
>
> What's the purpose of the exclamation marks?

Forcing; it means that the values are evaluated (up to WHNF) before the
Complex value is constructed:

http://www.haskell.org/ghc/docs/6.12.1/html/users_guide/bang-patterns.html

--
Ivan Lazar Miljenovic
Ivan.Miljenovic@gmail.com
IvanMiljenovic.wordpress.com