[Haskell-cafe] Question about HList possibilities
saynte at gmail.com
Mon Jun 25 10:39:47 EDT 2007
Given an HList (http://homepages.cwi.nl/~ralf/HList/) would it be
possible to do the following:
Create a class/function/magicks that would essentially do what
hOccursMany does, except it would not return a list of elements, but a
new HList. For example, would this allow us to be able to write more
lax typing constraints and say extract only things that are in lists.
ie) HCons "hi" (HCons [2.2,3.3] (HCons 'a' hNil)) -> HCons "hi"
(HCons [2.2,3.3] hNil)
(removing the Char element).
I tried to write something like this but I did not get very far, is it
even possible? I'm new to this type-level programming :)
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