[Haskell-cafe] Use unsafePerformIO to catch Exception?

Duncan Coutts duncan.coutts at worc.ox.ac.uk
Fri Mar 27 20:23:24 EDT 2009

On Fri, 2009-03-27 at 12:26 +0100, Henning Thielemann wrote:
> On Thu, 26 Mar 2009, wren ng thornton wrote:
> > Functions like uncons and viewL are nicer (because they're safe), but they 
> > can have overhead because they're unnecessarily complete (e.g. the Maybe 
> > wrapper can be avoided if we know a-priori that Just will be the constructor 
> > used).
> If you know, it's always Just, then don't use Maybe. There must be some 
> point in your program, from where it is sure, that it is always Just and 
> that is the point where to leave Maybe. When I searched my old code for 
> fromJust and head and review it carefully, I could eliminate them in most 
> cases.
> In another thread (Grouping - Map/Reduce)

Yes, grouping is the one where I most often find the need for head or
partial patterns. The function group produces a list of non-empty lists
but that is not reflected in the type. On the other hand, actually
reflecting it in the type would make it more awkward:

group :: Eq a => [a] -> [(a,[a])]


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