Case expressions, matching, and "constants"

[Bayley, Alistair]

I've just debugged a program that used a case expression, but where I was
trying to match on constants rather than literals. Here's a contrived
example:


> module Main where
> one = 1
> two = 2
>
> test n =
>	case n of
>		one -> "one"
>		two -> "two"
>		_ -> "three"
>
> main = putStrLn (test 2)


This initial version seems to me to be the "natural" way to write the case
expression, but it doesn't work because the first alternative always
succeeds.

This is what I've turned it into to get it to work. It seems a bit clumsy;
is there a better way to write this?

> test n =
>	case True of
>		_ | n == one -> "one"
>		  | n == two -> "two"
>		  | otherwise -> "three"


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