[Haskell-cafe] Re: Amazing

Lennart Augustsson lennart at augustsson.net
Sun Feb 15 17:15:14 EST 2009

It's true that you can do "program" the type checker even more if you
have dependent types, but first you should look into what you can do
in Haskell.  You can do a lot with type classes.

  -- Lennart

2009/2/15 Peter Verswyvelen <bugfact at gmail.com>:
> How practical is this dependent types thing? I hear a lot about this from
> really clever people who are usually 10 years ahead of their time :)
> Actually, back in the eighties when I was an assembly language hacker, I
> didn't want to switch to Pascal or C since I found the types in those
> languages too weak. C++ changed that with templates, and then I switched
> (only to find out that no C++ compiler existed that would not crash on my
> fully templated programs ;-).
> What I really wanted was a way to program the type checks myself; verify
> constraints/assertions at compile time, and if the constraint or assertion
> could not be done at compile time, get a warning or an error (or bottom if
> the custom type checking program is stuck in an endless loop ;-)
> Of course back then I was even more naive than I am now, so those things are
> easier said than done I guess.
> But if I understand it correctly, dependent types are a bit like that,
> values and types can inter-operate somehow?
> On Sun, Feb 15, 2009 at 9:40 PM, Stefan Monnier <monnier at iro.umontreal.ca>
> wrote:
>> > So IMO static typing is good, but it's only with functional programming
>> > that
>> > it really shines.
>> You can go one step further: if you start using dependent types, you'll
>> see that it gets yet harder to get your program to type-check, and once
>> it does, you don't even bother to run it since it's so blindingly
>> obvious that it's correct.
>>        Stefan
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