#2309: containers: specialize functions that fail in a Monad to Maybe

[Iavor Diatchki]

Hi,
I also like Maybe---it is simpler, it is what you want most of the time.
-Iavor

On Thu, May 29, 2008 at 6:57 AM, Jonathan Cast
<jonathanccast at fastmail.fm> wrote:
>
> On 29 May 2008, at 1:30 AM, Neil Mitchell wrote:
>
>> Hi
>>
>>>> Following this line of reasoning: why is  1  syntactic sugar for
>>>>  fromIntegral 1? If 1 has type Integer then the generic value is just a
>>>> fromIntergal away!
>>>
>>> That's a good point the other way --- I suspect, like most things Num,
>>> numeric literals were rather grand-fathered in than designed
>>> intentionally
>>> that way.
>>
>> fromIntegral is essential if you have two "integer" types, namely Int
>> and Integer. If you are looking for something to blame, then its the
>> premature optimisation that is Int. Int is really just a performance
>> hack around Integer.
>
> Um, that de-railed quickly...  'fromIntegral' in the original is a typo  or
> mis-understanding for 'fromInteger'.  My comment was re: implicit
> fromInteger (and polymorphic numeric literals).  GP was arguing for making
> Map.lookup polymorphic in the failure monad; I replied I thought, in the
> case of numeric literals, that no-one designing Haskell without the
> tradition that 3 `member` IR, no-one would have thought that 3 :: Integer
> and 3 :: Double both made sense.  Explicit conversions are not really the
> issue here.
>
> jcc
>
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