[Haskell-cafe] problem with IO, strictness, and "let"

[Andrew Coppin]

Stefan O'Rear wrote:
> On Fri, Jul 13, 2007 at 07:59:22PM +0100, Andrew Coppin wrote:
>   
>> Care to elaborate on "bad things"? (I.e., will this just crash the program 
>> with an error, or will it do something more serious?) I must admit, I 
>> thought closing such a file was simply no-op.
>>     
>
> If you close the file, the stream will suddenly end.  I believe silent
> data corruption is worse than a crash :)
>   

Agreed...! o_O

>> I can't remember why exactly, but somewhere or other I wrote some code that 
>> does this. (Basically I want to shut the file without reading all of it, so 
>> I can reopen it and start reading from the beginning again.) Is there a 
>> sane way to do this? Or am I going to have to start playing with explicit 
>> reads and writes? (Obviously I could just hang on to *all* of the input 
>> stream returned from getContents - but that could be quite large. The 
>> current way gives me low memory usage...)
>>     
>
> Did you actually try it?

I am not 100% sure about this. I wrote code that had an execution path 
that does this, but I don't know if I ever actually *excercised* it...

(The idea was to read, say, 10% of the file, and then close it and start 
reading from the beginning again.)

How about redundantly closing the file after you've already read all of 
it anyway? Is that dangerous?