[Haskell-cafe] Avoiding parametric function binding
quick at sparq.org
Tue Jan 3 07:46:18 CET 2012
On Sun, 01 Jan 2012 05:29:42 -0700, Sebastian Fischer <fischer at nii.ac.jp>
> On Sat, Dec 31, 2011 at 4:09 PM, Kevin Quick <quick at sparq.org> wrote:
>> onVarElem :: forall a . (Show a) => (Maybe a -> String) -> Var ->
> The problem is the scope of the quantification of the type variable 'a'.
> You can use higher-rank types (via the Rank2Types or RankNTypes language
> extension) to achieve what you want. Change the type of 'onVarElem' to
> onVarElem :: (forall a . (Show a) => Maybe a -> String) -> Var ->
Thanks to both Sebastian and Sean for the solution (abbreviated from
Sebastian's reponse above).
P.S. Sorry for the late followup: some minor system issues prevented
checking email for a little while. The delay notwithstanding, *all* of
the responses were much appreciated.
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