[Haskell] help with some basic code that doesn't work
Malcolm.Wallace at cs.york.ac.uk
Tue Feb 8 06:19:34 EST 2005
Matthew Walton <matthew at alledora.co.uk> writes:
> (==) works on types which are members of the Eq typeclass. You can
> define this instance manually, or, since your type is nice and simple,
> you can get Haskell to derive it for you.
Just a comment, since a couple of people have made similar statements.
Haskell will derive Eq for arbitrarily complex types - there is no
restriction to "simple" types, whatever they might be. It will
always give you the "obvious" structural equality. There /are/
occasions when structural equality is not quite what you want, but
that decision is entirely orthogonal to whether the type definition
is simple or complex.
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