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

Jonathan Cast jonathanccast at fastmail.fm
Tue Oct 14 18:45:29 EDT 2008

On Tue, 2008-10-14 at 22:28 +0400, Alexey Romanov wrote:
> On Tue, Oct 14, 2008 at 9:14 PM, Jonathan Cast
> <jonathanccast at fastmail.fm> wrote:
> > On Tue, 2008-10-14 at 18:15 +0100, John Lato wrote:
> >> Are you advocating introducing existential types to beginning
> >> Haskellers?  I think something with the scary name
> >
> > Invalid argument.
> >
> >> "existential
> >> quantification" would greatly increase the head'splodin' on the
> >> learnin' slope.
> >
> > Invalid argument.  Head explosion is the *goal* of teaching Haskell.
> Is it? I would certainly prefer my students to say "This is obvious. Why would
> things work in any other way?"

Sure.  But I see head explosion as a means to that end (in the finest
tradition of functional languages, from lisp onward).

> They don't, but I can dream.
> >> Certainly there's a place for them, but I wouldn't
> >> want to see new Haskell programmers habitually approach problems with
> >> a "first create a type class, then make an existential wrapper"
> >> mentality.
> >
> > Of course not.  That's just translating OO into Haskell.  Personally, I
> > would avoid comparing Haskell to other language at all (SOE I believe
> > takes this approach).

> I find such comparisons pretty useful.

What kind of comparisons?  Translations between languages or comparisons
of idioms (which usually involve quite different factorings)?  And
useful for getting students to be quiet, or useful for getting them to
produce idiomatic Haskell?


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