[Haskell-beginners] Traversing generic trees

[Bob Ippolito]

You should not try and use the built-in lists or tuples to represent a tree
data structure. That's not what they're good at. You probably could make
tuples work and write functions using GHC.Generics to work with it as a
tree data structure, but it definitely won't be easy or elegant. If you
want a more economic syntax for expressing the tree you can provide shorter
names for Leaf and Node (one char isn't too bad), or else you're stuck with
using a parser. You may not have to write a parser though, perhaps JSON or
YAML would work fine for this. If it needs to go in the source file,
there's always TemplateHaskell and QuasiQuotes.

On Thu, Jul 23, 2015 at 9:48 AM, Ali Baharev <ali.baharev at gmail.com> wrote:

> Dear All,
>
> I used to work at the University. Whenever a student asked me a
> question, I first focused on the question and tried to answer it.
> Sometimes the question was tough, maybe because there wasn't any easy
> solution to the problem. In those situations I used to say to my
> students: “Problem well spotted, unfortunately I cannot give you an
> answer / there is no easy solution to this problem.” However, I have
> never started questioning the questions of my students, especially
> when I could not give them an answer.
>
> According to the Wiki on beginners at haskell.org: "Here, there is no
> such thing as a 'stupid question.'" If you start questioning my
> question, then I really do not know where to go...
>
> You might as well say: The whole question is pointless, just use
> Data.Tree and be done with it!
>
> It is really not part of the original question, and I sooo not want to
> get into a discussion over this: It is important to have language
> support for helping humans to input data, without a full-blown parser.
> Examples would be user-defined implicit type conversions and
> user-defined literals in other statically typed languages.
>
> OK, let's get back to the original question.
>
> Apparently, there is no easy way to solve it with nested lists.
> However, no one has touched the nested tuples so far. How can I write
> a toString function that works similarly to mine but destructures
> arbitrarily nested tuples?
>
> Thanks,
>
> Ali
>
> On Thu, Jul 23, 2015 at 9:41 AM, Imants Cekusins <imantc at gmail.com> wrote:
> > .. on the other hand, if facing this problem:
> > - import large trees from concise human-readable representation as string
> >
> > , it is probably possible to write a parser which does just that.
> >
> > After all json parser works somehow ;)
> >
> > Just saying that you could do this in Haskell, given enough interest.
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