[Haskell-cafe] Deduce problem.
magicloud.magiclouds at gmail.com
Thu Nov 17 06:44:08 CET 2011
On Thu, Nov 17, 2011 at 1:17 PM, Brandon Allbery <allbery.b at gmail.com> wrote:
> On Wed, Nov 16, 2011 at 23:54, Magicloud Magiclouds
> <magicloud.magiclouds at gmail.com> wrote:
>> I think this is where I did not understand from the very beginning.
>> If the the declaration was correct, then why cannot b be H?
>> Referring to Data.List.genericLength, I was confused.
> Because it doesn't mean that *you* get to decide what it is; it means *the
> caller* gets to decide, and you are obligated to honor the caller's wishes.
> Returning always an H violates this, because there is no way to prove that
> H is the only possible response.
> brandon s allbery allbery.b at gmail.com
> wandering unix systems administrator (available) (412) 475-9364 vm/sms
Ah, list and single value is a typo problem.
So I think I got what you guys meant, I limited ClassB to only H.
Then how to archive my requirement, that from and to only return items
that instanced ClassB?
More information about the Haskell-Cafe