[Haskell-beginners] How best to do this?

Michael Peternell michael.peternell at gmx.at
Wed May 1 12:35:36 CEST 2013

By reading your mails I got an idea...

how about generating a compiler warning when someone types a literal like [5..2].

"Foo.hs:32: Warning: Literal list [5..2] evaluates to [] because 5 > 2 and the default step size is +1. Replace the literal with the empty list or with [5,4..2] to suppress this warning."

That would be a really beginner-friendly warning.

But I also think that we shouldn't catch this kind of mistake at runtime, because it may be the expected behavior in many cases.


Am 29.04.2013 um 23:54 schrieb Brent Yorgey:

> Oh, yes, I suppose it could.
> In any case, I am still in favor of the existing semantics -- it is
> simple and consistent (and sometimes even useful).  "Do what I
> mean"-style semantics with special cases end up generating more pain
> than they solve.
> -Brent
> On Mon, Apr 29, 2013 at 02:29:43PM -0400, David McBride wrote:
>> Couldn't it just use fromEnum and compare the integers you get and
>> figure out which is bigger?
>> On Mon, Apr 29, 2013 at 2:17 PM, Brent Yorgey <byorgey at seas.upenn.edu> wrote:
>>> But then \x y -> [x .. y]  would have to have the type
>>>  (Ord a, Enum a) => [a]
>>> whereas now it just has the Enum constraint.  Either that or else the
>>> notation would work differently for literals vs. expressions but that
>>> would be just awful.
>>> -Brent

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