Removal candidates in patterns

Duncan Coutts duncan.coutts at
Thu Jan 26 13:37:13 EST 2006

On Thu, 2006-01-26 at 17:31 +0000, Simon Peyton-Jones wrote:
> I agree that if (n+k) patterns go, then so should k patterns.  Both are
> overloaded, and that's the root of their complexity.

I have to say that we use 'k' patterns in teaching all the time, though
we do not teach n+k patterns. There are lots of cases where it's
convenient to say:

foo 0 = ...
foo n = ...

Intuitively it seems reasonable to me that 1 is a constructor for the
Int type just as 'c' is a constructor for type Char, and since it's a
constructor we can pattern patch on it.

To be honest, the difficulty of the internal translation needed for
tools seems less important to me than the convenience for users. I don't
think the difference that character constants are not overloaded where
as numeric constants are overloaded causes any difficult in
understanding for users.


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