[Haskell-cafe] Equality constraints in type families

Wolfgang Jeltsch g9ks157k at acme.softbase.org
Thu Mar 27 20:53:59 EDT 2008

Am Donnerstag, 27. März 2008 23:12 schrieben Sie:
> The reason for the braces in type families is because type indices are
> treated differently than normal parameters. I don't think this should be
> adopted for type synonyms either.
> Cheers,
> hugo

In a way, there is also different treatment in the case of type synonyms.  If 
you have the definition

    type ReaderWriterT m = ReaderT (WriterT m),

you cannot leave out the m but you can leave out the result type parameter.

I think, it would be good if the syntax of type synonyms and type synonym 
families was consistent.

Best wishes,

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