If a newbie considers this as something natural, this is another reason for syntactic sugaring of HList:
http://www.haskell.org/pipermail/haskell-cafe/2011-April/090986.html 2011/10/2 Du Xi <sdiy...@sjtu.edu.cn> > --I tried to write such polymorphic function: > > expand (x,y,z) = (x,y,z) > expand (x,y) = (x,y,1) > > --And it didn't compile. Then I added a type signature: > > expand::a->b > expand (x,y,z) = (x,y,z) > expand (x,y) = (x,y,1) > > --It still didn't compile. I think the reason is that the following is > disallowed: > > f::a->b > f x = x > > --Is it possible to get around this and write the "expand" function? Of > course, x and y may be of different types > > > > ______________________________**_________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/**mailman/listinfo/haskell-cafe<http://www.haskell.org/mailman/listinfo/haskell-cafe> >
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