[Haskell-cafe] Re: Hints for Euler Problem 11

[Jon Fairbairn]

Kim-Ee Yeoh <a.biurvOir4 at asuhan.com> writes:

> Aaron Denney wrote:
> > I find the first far more readable.  The compiler should be able to
> > assemble it all at compile time, right?
> > 
> 
> 'Course not. The (++) function like all Haskell functions is only a
> /promise/ to do its job.

I find this comment rather strange.  One of the beauties of
a pure language (especially a lazy one) is that there is no
requirement for evaluation to take place at at any
particular time as long as it's done before it's needed. So
the compile-time/run-time dichotomy is only relevant when a
value depends on data only available at run-time.

Given that "foo "++"bar" can be evaluated at compile time
and there are advantages and no disadvantages, it should be
evaluated at compile time. In general, I don't think we
should clutter the language with syntax for things for which
there has to be a more general mechanism; including string
breaks in the language was a mistake.

Compare

   "thing1\n\
   \thing2\n\
   \thing3\n"++
   otherThing++
   "penultimate thing\n\
   \last thing\n"

with

   "thing1\n"++
   "thing2\n"++
   "thing3\n"++
   otherThing++
   "penultimate thing\n"++
   "last thing\n"

What /is/ the advantage of the former?

-- 
Jón Fairbairn                                 Jon.Fairbairn at cl.cam.ac.uk