[Haskell-cafe] feasability of implementing an awk interpreter.

[Jason Dagit]

On Thu, Aug 19, 2010 at 8:05 PM, Michael Litchard <michael at schmong.org>wrote:

> I'd like the community to give me feedback on the difficulty level of
> implementing an awk interpreter. What language features would be
> required? Specifically I'm hoping that TH is not necessary because I'm
> nowhere near that skill level.
>

I'd love to have portable pure haskell implementations of the traditional
unix tools.  If it were done well, it would allow you to 'cabal install'
yourself into a usable dev environment on windows :)  I'd much rather do
that than deal with cygwin/mingw.

Someone (was it Stephen Hicks?) was writing (or finished writing?) an sh
parser and I got really excited for the same reason.  It would be a cool
project, but I'm not sure I can justify to myself spending my spare cycles
on it.


>
>
> An outline of a possible approach would be appreciated. I am using
> http://www.math.utah.edu/docs/info/gawk_toc.html
> as a guide to the language description.
>

I think this is a good opportunity for you to learn about monad
transformers.  To that end, I think you will like this paper (quite easy for
beginners to pick up):
http://www.grabmueller.de/martin/www/pub/Transformers.en.html

At least, that's how I first learned about them and I though it was easy to
read at the time :)

You might also want to read (and try) some of the tutorials that focus on
creating interpreters just to sort of get some practice in that area.  I
haven't read it, but I've heard good things about this one:
http://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours

You might also focus on the 'core' of awk.  Think about, what is the minimal
language and start from there.  Grow your implementation adding features bit
by bit.  It's also a good opportunity to do testing.  You have a reference
implementation and so you can write lots of tests for each feature as you
add them.

I hope that helps,
Jason
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