[Haskell-cafe] Typed Configuration Files

Ketil Malde ketil at malde.org
Fri Jan 15 03:54:21 EST 2010

Neil Mitchell <ndmitchell at gmail.com> writes:

> The CmdArgs manual might help:
> http://community.haskell.org/~ndm/darcs/cmdargs/cmdargs.htm

Yes, this is what I used :-)  Presenting examples is great, but gives me
the hubris to rip off the example that seems to fit most closely, and
modify it.  This makes for a quick start, but also for the odd

> I'd describe cmdargs as referentially impure, but really concise.

Concise is nice - I've often been a bit annoyed that the otherwise nice
GetOpt stuff forces me to write a lot of boilerplate, enough of it that
my programs usually have a separate Options module.  For a lazy slob
like me, this means I often just hack something on top of the raw
GetArgs or write half-baked but simple solutions like my simpleargs

> 'def' is the default value, empty has a particular semantic meaning
> and serves to change the options. I should document this more
> carefully. Perhaps empty should be renamed 'optional', since that's
> what it does.

'whenMissing'?  'unspecified'?

>> - As I wanted a single file argument, I tried to use 'args' in
>>  combination with a parameter of type FilePath.  Apparently 'args'
>>  wants [FilePath] and appends command line arguments to the default
>>  value. 

Spoilt by Haskell, I'd have expected a type error here.

> argPos 0 should do the trick.

Right.  Will subsequent arguments be ignored?

> CmdArgs is very much a 0.1 release. The documentation isn't polished,
> it does simple arguments nicely, but has flaws when you try and go
> more advanced. I want to spend some more time on it at some point.

That's great, I'm looking forward to it.

If I haven't seen further, it is by standing in the footprints of giants

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