[Haskell-cafe] Re: Type classes: Missing language feature?
apfelmus at quantentunnel.de
Tue Aug 7 09:46:16 EDT 2007
> newtype Lex = Lex Monomial deriving (Eq)
> newtype Glex = Glex Monomial deriving (Eq)
> Now, what I'd like to do is have Lex and Glex, and any further monomial
> orderings I define later, automatically derive Show and Num instances from
> Monomial (because it seems like boilerplate to have to define Show and Num
> instances by hand).
Good news: it's already implemented and called newtype deriving :)
In short, you just write
newtype Lex = Lex Monomial deriving (Eq, Show, Num)
I guess that the Show instance will add the constructor Lex , though.
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