[Haskell-cafe] reading existential types
mailing_list at istitutocolli.org
Fri Jul 13 13:59:29 EDT 2007
On Mon, Jul 09, 2007 at 09:41:32PM +0100, Claus Reinke wrote:
> hiding concrete types in existentials sometimes only defers problems
> instead of solving them, but exposing class interfaces instead of types is a
> useful way to mitigate that effect. it just so happens that this particular
> problem, reading an existential type, slightly exceeds that pattern, as
> 'read' needs to know the hidden type to do its job ('read' does not
> determine the type from the input form, but uses the type to determine what
> form.the input should have).
> a workaround is to try to read all possible types, then hide the type again
> once a match is found. the main disadvantage of this method is that we need
> a list of all the types that could possibly be hidden
As a follow up, mainly meant to thank you, I wanted to let you know
that I adopted this approach in a piece of software I'm writing.
It's a status bar for the XMonad Window Manager, the tiling WM written
Actually it is a text based status bar that can be used with any
WM, but we love XMonad particularly...;-)
More information about this status bar can be found here:
with link to the source code, a screen shot and eve a link to a
I obviously credited you for the help and the code!
One again, thank you.
All the best,
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