[Haskell-cafe] GADTs vs arrows/typeclasses

Henrik Nilsson nhn at Cs.Nott.AC.UK
Wed Dec 6 18:02:20 EST 2006

Dear all,

S. Alexander Jacobson wrote:

 > I don't think I'm the only one confused here.  Henrik Nilson in his
 > paper on adding GADTs to Yampa comments that:
 > ...
 >   In particular, GADTs are just what is needed to address the problem
 >   discussed above since the key idea is to allow constructors that
 >   have more specific types than usual, and to take that extra type
 >   information into account in individual case branches. GADTs would no
 >   doubt also offer an interesting alternative to the methods described
 >   by Baars and Swierstra [1] and Hughes [19].
 > [1] and [19] are papers about Arrows.

I categorically deny being confused! :-)

The comment refers to the methods Baars, Swierstra, and Hughes employ
to encode type equality in order to be able to perform optimizations
along similar lines as outlined in my paper.

I was not at all proposing to use GADTs in place of arrows, and
I cannot really see how the quote can be read as suggesting that. As
Neil has already said: GADTs and arrows are just different kinds of



Henrik Nilsson
School of Computer Science and Information Technology
The University of Nottingham
nhn at cs.nott.ac.uk

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