Re: [Haskell-cafe] IO and lazyness.

On Mar 6, 2007, at 16:22 , D.V. wrote:

On 3/6/07, mm wrote:

...

I cannot help you with your question more than pointing you to

http://bugs.darcs.net/issue391

where Simon Marlow explains how to avoid "IO.bracket".

I'm using Control.Exception's bracket.

Also, following Jeremy's advice, I replaced the last line of rechf2 with return $! rech r $ lines f and indeed it works.

I don't understand why it doesn't without the !

The documentation for hGetContents says the items are read on demand. the function rech needs the strings so they should be read on demand. This confuses me :(

Because rech is lazy so it only reads them when something demands it do so (e.g. IO, or $! which forces strict evaluation). -- brandon s. allbery [linux,solaris,freebsd,perl] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH