What are you trying to acomplish? A case doesn't necessarily force
evaluation in haskell depending on the binding pattern. for instance
case x of _ -> undefined will parse, but the function is still lazy in
x. it is exactly equivalant to
quodlibet x = undefined
If you want to actually enforce that quodlibet _|_ evaluates to _|_
then you want quodlibet x = x `seq` undefined. Though, that too is
technically equivalent in a theoretical sense, but may have practical
benefits when it comes to error messages depending on what you are
trying to acomplish.
John
On Sun, Oct 9, 2011 at 4:26 AM, Roman Beslik
Hi.
Why the following code does not work?
data Empty quodlibet :: Empty -> a quodlibet x = case x of "parse error (possibly incorrect indentation)"
This works in Coq, for instance. Demand for empty types is not big, but they are useful for generating finite types:
Empty ≅ {} Maybe Empty ≅ {0} Maybe (Maybe Empty) ≅ {0, 1} Maybe (Maybe (Maybe Empty)) ≅ {0, 1, 2} etc. Number of 'Maybe's = number of elements. I can replace @Maybe Empty@ with @()@, but this adds some complexity.
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