[Haskell-cafe] Harder than you'd think

[Andrew Coppin]

Philippa Cowderoy wrote:
> On 13/06/2010 14:52, Andrew Coppin wrote:
>> Marc Weber wrote:
>>>> Does anybody have a less-insane way of doing this?
>>>
>>> Sure:
>>>   type MyMap = Map (KeyID, Key) Value
>>>
>>> Don't use multiple keys. Put the keys into a tuple and use that as key.
>>>
>>> Let me know whether this is what you were looking for.
>>
>> Trouble is, this requires you to have *all* the keys to perform a 
>> single lookup. You can't do a lookup on just one attribute.
>>
>
> No it doesn't - think sum/or, not product/and, your tuple's (KeyID, 
> Key) not (Key1, Key2, Key3...).
>

Oh, I see - so you enter (1, author), (2, date), (3, time), etc?

That then requires all keys to have the same type - although I think for 
my needs I can put together an ADT to fix that...