Haskell 1.3 (n+k patterns)

[John Launchbury]

I feel the need to be inflamatory:

  I believe n+k should go.

There are lots of good reasons why they should go, of course. The question
is: are there any good reasons why they should stay? My understanding is
that the only reason they are advocated is that they make teaching
induction easier. I don't believe it. I teach an introductory FP course
including induction. I introduce structural induction directly, and the
students have no problem with it. When I have tried to talk to individuals
about natural number induction using (n+k) patterns, then the problems
start. Because they are so unlike the form of patterns they have become
used to they find all sorts of difficulties. What if n is negative. Ah yes,
well it can't be. Why not. It just can't. etc.

Let's throw them out.

John.

Re: Haskell 1.3 (n+k patterns)

[Lennart Augustsson]

jl writes:
> I feel the need to be inflamatory:
> 
>   I believe n+k should go.
Again, I agree completely.  Let's get rid of this horrible wart
once and for all.  It's a special case that makes the language
more difficult to explain and implement.  I've hardly seen any
programs using it so I don't think backwards compat is a problem.
Anyone who thinks this change will cause them more than 10
minutes work, plese speak up.

-- Lennart