[Haskell-cafe] HSpec vs Doctest for TDD

Francesco Ariis fa-ml at ariis.it
Wed Jun 25 16:26:06 UTC 2014

On Wed, Jun 25, 2014 at 11:47:23AM -0400, Michael Orlitzky wrote:
> On 06/25/2014 11:24 AM, Francesco Ariis wrote:
> >
> > For non-believers, here is a blog post that opened my eyes on the matter [1].
> >
> > [1] http://lambda.jstolarek.com/2013/12/data-is-evidence/
> None of that helps if you write the wrong program. Your program may
> typecheck, but if you're expecting "42" as output and your program hums
> the Star Trek theme instead, the fact that it correctly does the wrong
> thing won't be much consolation.

    data Hum = HumStarTrekTheme
             | CountrySong

    data UltimateAnswerToEverything = FourtyTwo

    {- assorted datatypes and functions -}

    program :: a -> UltimateAnswerToEverything

Getting serious again, the author of the post states:

    " A type system can be regarded as calculating a kind of static
      approximation to the run-time behaviours of the terms in a program.

and then delivers (i.e. |order zero (suc b) = ge ge0| won't typecheck).

I cannot but feel 90%+ of tests are just an "ad hoc, bug ridden, informally
specified" type system.

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