String != [Char]

[Gábor Lehel]

On Sun, Mar 25, 2012 at 5:19 AM, Greg Weber <greg at gregweber.info> wrote:
> On Sat, Mar 24, 2012 at 7:26 PM, Gabriel Dos Reis
> <gdr at integrable-solutions.net> wrote:
>> On Sat, Mar 24, 2012 at 9:09 PM, Greg Weber <greg at gregweber.info> wrote:
>
>>> Problem: we want to write beautiful (and possibly inefficient) code
>>> that is easy to explain. If nothing else, this is pedagologically
>>> important.
>>> The goals of this code are to:
>>>  * use list processing pattern matching and functions on a string type
>>
>> I may have missed this question so I will ask it (apologies if it is a
>> repeat):  Why is it believed that list processing pattern matching is
>> appropriate or the right tool for text processing?
>
> Nobody said it is the right tool for text processing. In fact, I think
> we all agreed it is the wrong tool for many cases. But it is easy for
> students to understand since they are already being taught to use
> lists for everything else.  It would be great if you can talk with
> teachers of Haskell and figure out a better way to teach text
> processing.
>

I think a helpful question might be whether [Char] is mainly used to
teach about lists, or whether it's mainly used to teach about how to
do Unicode text processing correctly. If it's mainly used to teach
about lists, pattern matching, etc., as I suspect, then the fine
details of Unicode don't matter so much, you could even work with
ASCII-only strings and it would work equally well for teaching about
lists. How to do Unicode text processing correctly is a topic that
seems like it would become important much later, when someone's going
to write code that's meant to be used in a production environment.
Most students in an introductory university course probably don't get
close to that point. If you do want to teach about how to do Unicode
text processing correctly (which, for the record, is an important
issue irrespective of which programming language you're using) then
presumably you want to teach about Text, but hopefully your students
will be more advanced by then and it won't be so much of a problem.

I'm not really sure what that recommends in terms of policy. Mainly
what you need is "it should be possible to work with lists of
characters" and "it should be possible to work with Text", which we
more-or-less have already. The important bits seem to be
OverloadedStrings and ideally some way to avoid a pervasive API bias
towards the wrong type (the tradeoffs there are probably more tricky).
(So... basically what Simon M. said.)