[Haskell-cafe] Recursive timezone-loading function

Yitzchak Gale gale at sefer.org
Thu Nov 29 23:28:45 CET 2012

Hi David,

David Thomas wrote:

> https://github.com/dlthomas/tzcache
> A small bit of code, but seems likely to be useful enough that I figured I
> should share.

Thanks for sharing this!

> 1) Does this already exist somewhere I missed?

I haven't seen it anywhere.

> 2) It seems silly to make this its own library

 - any suggestions where it could be added?

If you feel it is appropriate, I would be willing to add it
to timezone-olson. Does anyone else have an opinion
about it?

3) Is the traverse-a-directory-and-populate-a-map

pattern one worth abstracting?  If so, where should that go?

I think the proper abstraction would be a more
general fold or traversal over a directory structure.
Some languages have something like that (e.g.,
os.walk in Python). But look how simply it worked
out for you in Haskell - perhaps that's why there
doesn't seem to be a standard function for this
anywhere. That said, it might be interesting to
have this as a lens-package-style traversal.

4) Presently, it's a static cache entirely pre-loaded.

This seems fine, as it's not a terribly huge amount

of data, but it's worth noting.

Yes. The total amount of timezone data in the world
is likely to continue increasing at a significantly
slower rate than Moore's law.

5) Any comments on the code generally?

Improvements?  Complaints?

I like your code. I'm not sure how well this
brute-force mapM recursion would scale over
a timezone directory structure with, say, millions
of nodes. But that's not the use case here at all.

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