Am Freitag, 26. März 2004 09:19 schrieb Robert Will:
On Tue, 23 Mar 2004, Malcolm Wallace wrote:
Multi-parameter type classes, as used in your proposal, are also a language extension. Every implementation that supports MPTC also supports fundeps.
Hair-splitting reply: MPTC are not an extension, but the suppression of a restriction.
Then every so-called language extension is the suppression of a restriction since it allows Haskell programs which were incorrect before. ;-)
Not being restricted to one TC parameter is also a simplification in some sense... FunDeps, otoh, are a completely new concept.
But they are often needed or at least useful when MPTCs are used.
Honest reply: I don't fully understand FunDeps and I don't want to learn (now), since the Collections should also be understandable for people less intelligent than me. (This is a design criterion used throughout, and I think my not-too-high intelligence has made this one of the Collection's success factors!)
Fundeps basics are not so difficult to understand IMHO, at least if you have some database background. A one-parameter type class defines a predicate on the types, a multi-parameter type class defines a relation, and a MPTC with fundeps defines a relation with functional dependencies just like in relational database technology.
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