[Haskell-cafe] whine and solution about programmers not respecting documentations

Luke Palmer lrpalmer at gmail.com
Mon Jun 28 17:29:22 EDT 2010

On Mon, Jun 28, 2010 at 1:44 PM, Albert Y.C.Lai <trebla at vex.net> wrote:
> Why should anyone expect
>  deleteBy (>=) 5 [0..10]
> to accomplish anything meaningful, if he/she respects the written docs?

I proposed the following solution:


> Today someone on #haskell expected it to accomplish something meaningful,
> even something mind-reading. The said person has been around for more than
> a year, not eligible for the "newbie" excuse. The said person is just the
> tip of an iceberg.
> The doc of deleteBy states: "The deleteBy function behaves like delete, but
> takes a user-supplied equality predicate." A precondition is that the
> user-supplied predicate is an equality predicate. (>=) is not an equality
> predicate, be it in the layperson sense of "it isn't analogous to (==)" or the
> mathematical sense of "it isn't an equivalence relation".
> If you respect the precondition or the authors of the doc, you should just
> never use deleteBy (>=) 5 [0..10], much less expect any meaningful result.
> I propose this solution:
> For each of deleteBy, groupBy, unionBy... we can usually conceive at least two
> implementations, behaving pretty much the same (answer, speed, space) when
> given an equivalence relation (modulo some rare concern when the equivalence
> relation has assymetric strictness properties), but behaving different when
> not, and their code sizes are pretty much the same. With more imagination and
> allowing some code bloat, perhaps we can conceieve more implementations. But
> two suffices, really.
> I propose that at each minor version of base, someone picks an implementation
> randomly.
> Here is a more radical, less labour-intensive solution, if you don't mind a
> judicious, correctness-preserving use of unsafePerformIO: at the first
> invocation of the process lifetime, pick an implementation randomly.
> The result frustrates people who disrespect the docs. My purpose is exactly
> that. The goal is to give people an incentive to not disrepect the docs.
> (If you think this is a nasty "stick, not carrot" incentive, on first thought I
> would agree. On second thought, it is not adding a stick, it is just removing a
> carrot. Programmer's carrot means his/her code "works" consistently. When
> deleteBy (>=) "works" consistently, you are giving out undeserved free carrots
> --- incentive to write more wrong code. I am proposing to remove undeserved
> free carrots.)
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