[Haskell-cafe] Re: What I wish someone had told me...

John Lato jwlato at gmail.com
Tue Oct 14 11:44:34 EDT 2008

While this may be true, it's missing the point.  The claim that type
classes are like interfaces (the usual argument is that they define an
interface, but not an implementation) misleads OO-grounded programmers
into thinking of type classes in terms of an already-familiar concept.
 This is bad because said programmers then attempt to apply familiar
OO-styles, when they would be better off abandoning most of what they
already know about design.  I don't mean in the sense of "abstraction
good, separation of processing good, repetition bad", but rather how
to develop a useful/stable API, how to divide up the different
processing the module should do, etc.  In short, how to approach API
design, which is very different in Haskell than the practice that most
OO disciples are familiar with.

IMHO, stating that type classes act like interfaces in argument types,
but not return types, is too complicated a relationship to be useful
to somebody's first introduction to FP.  Better to avoid the whole
issue completely.

John Lato

Alexey Romanov wrote:
> Well, they act like interfaces in argument types, just not variable or
> return types.
> Yours, Alexey Romanov

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