[Haskell-cafe] extending and reusing cmdargs option specs ?

Simon Michael simon at joyful.com
Mon Aug 8 19:59:13 CEST 2011

Hi Neil,

I just spent a day converting hledger from getopt to cmdargs. cmdargs  
feels more high level and featureful and nicer. And yet... I haven't  
reduced the line count that much - nothing like your HLint 3:1 ratio.  
And, I may have made things worse for myself in the reuse/avoiding  
boilerplate department: I'm not sure how to reuse a cmdargs options  
data structure, extending it with a few more options. Using getopt I  
was able to do this without repeating myself (as long as I defined the  
full set of Opt constructors in one place.) I've looked at the more  
advanced cmdargs api, but don't see a way yet - would you have any  
ideas ?

I want this because I have multiple executables (hledger, hledger-vty,  
hledger-web etc.) which should share most (but not all) options. Also,  
I'd like to move a generic subset of report options, without the ui- 
specific ones, into hledger-lib for use by all apps.

Also, the hledger executable has multiple commands, so I'd like to  
define a mode for each, but not have to redeclare all the same options  
for each mode - I didn't see how to do that.

As always, thanks a lot for cmdargs!

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