[Haskell-cafe] Re: New Hackage category: Error Handling
lemming at henning-thielemann.de
Mon Dec 7 19:15:50 EST 2009
On Tue, 8 Dec 2009, Richard O'Keefe wrote:
>> X/0, sqrt(-1), head  are errors
> It depends on WHERE THE DATA CAME FROM.
If your program actually computes X/0 or sqrt(-1) or head  your program
is buggy, independent from where the zero, the minus one or the empty list
>> Sure, the distinction exception/error depends on the source of the data
>> that causes problems.
> And sadly, the library does not know this, so the library cannot classify
> problems _that_ way.
To this end the library documentation says: "Precondition: This function
must only be called on non-empty lists." If the programmer calls it with
an empty list anyway, it's his fault. The library user made the error
then. Of course it would be better, if types or contracts could force such
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