[Haskell-cafe] Exception handling when using STUArray

Jonathan Cast jonathanccast at fastmail.fm
Mon Mar 10 20:48:29 EDT 2008

On 10 Mar 2008, at 12:37 AM, Donn Cave wrote:

> On Mar 9, 2008, at 1:07 PM, Henning Thielemann wrote:
>> Errors are programming errors and must be fixed as Denis  
>> explained. Thus
>> there is no need for a complex system of handling these situations at
>> run-time. The program error might be unexpected but it isn't the  
>> fault of
>> the user or of the context the program runs in but of the fault of  
>> the
>> programmer. The program may report "bug detected, send an e-mail  
>> to the
>> author" but eventually it should quit (at least the buggy thread)  
>> before
>> worse things happen. This is possible in Haskell but should not be  
>> mixed
>> up with handling of exceptions like "non-existing file".
> I am not sure I see the difference in principle that you see.
> An exception is, for me, any state that isn't properly accounted  
> for in its
> immediate context.  openFile could return 'Maybe Handle', but it  
> doesn't,
> so the context demands a Handle or an exception.

In the context of this discussion, `Maybe Handle' /is/ an exception  
type, because Maybe is an exception monad.  As is IO.  This  
distinction is one between an unusual-but-anticipated code path, and  
a case the programmer simply didn't handle at all.  The former is an  
exception; the latter is an error.


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