2-tuple and 3-tuple *are not the same type*.
So to do this you must use typeclasses.
Plus you have to deal with the type parameters
class To3Tuple a where
expand :: a -> (Int, Int, Int)
instance To3Tuple (Int, Int, Int) where
expand = id
instance To3Tuple (Int, Int) where
expand (x,y) = (x,y,1)
Here I had to force my tuples to be tuples of integers.
It's more complicated if you want polymorphism.
2011/10/2 Du Xi
--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
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