[Haskell-cafe] Amazing

Conal Elliott conal at conal.net
Sun Feb 15 22:44:38 EST 2009

Hi Peter,

I'm delighted to hear about your successes with Haskell programming!

I suspect that parametric polymorphism has a lot to do with phenomenon of
works-when-it-compiles.  The more polymorphic a signature is, the fewer the
possible type-correct definitions.  Luckily, the definition that "works" is
one of the few type-correct ones.  As John Reynolds and then Phil Wadler
showed, some useful properties necessarily hold purely as a consequence of
the polymorphic type, regardless of the implementation.  (See "Theorems for

  - Conal

2009/2/14 Peter Verswyvelen <bugfact at gmail.com>

> One of the things I liked a lot when working with C# was that as soon as my
> code compiled, it usually worked after an iteration of two.At least if we
> forget about the nasty imperative debugging that is needed after a while
> because of unanticipated and unchecked runtime side effects.
> After heaving read about Haskell and having written some small programs for
> the last year or so, I'm now finally writing a bigger program with it. It is
> not so easy yet since learning a language and trying to reach a deadline at
> the same time is hard :)
> However, it is just amazing that whenever my Haskell program compiles
> (which to be fair can take a while for an average Haskeller like me ;-), it
> just... works! I have heard rumors that this was the case, but I can really
> confirm it.
> A bit hurray for strong typing! (and if you don't like it, you can still
> use Dynamic and Typeable ;-)
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