[Haskell-cafe] Type trickery
lrpalmer at gmail.com
Wed Mar 16 21:03:51 CET 2011
On Wed, Mar 16, 2011 at 7:52 AM, Andrew Coppin
<andrewcoppin at btinternet.com> wrote:
>>> Hmm, yes. That will work, but I wonder if there's some way of doing this
>>> that doesn't limit the scope of the container to one single span of
>> You can write helper functions which take containers as argument by
>> parameterizing these helper functions over s:
>> takesTwoContainers :: Container s1 -> Container s2 -> ...
>> takesTwoContainers c1 c2 = ... -- c1 and c2 can be used here
>> This function could be called like this:
>> withContainer (\c1 ->
>> withContainer (\c2 ->
>> takesTwoContainers c1 c2)) -- c1 and c2 can be used here
>> In this example, the scope of the containers is not limited to a single
>> span of code.
> What you can't do is write functions such as
> foo :: Container x -> (Cursor x, Cursor x)
> for example.
I don't follow.
foo = cursor &&& cursor
Did you mean to have some extra condition on foo that can't be satisfied?
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