[Haskell-cafe] sections for record settors

Neil Mitchell ndmitchell at gmail.com
Tue Sep 19 17:36:58 EDT 2006


I agree that a function syntax for a record setter is a really good idea.

> Consider for example an cmd line parser that collects flags in
> a record.  Instead of writing:
>      opt "l" (NoArg  {c_loop=False})        "dont loop",
>      opt "o" (optStr {c_out=} "dir")        "output dir",
>      opt "t" (optInt {c_maxtime=} "mins")   "maximum time"

Just to show that this is a perfect example, see
which has exactly the kind of problem you mention. Because there is no
setter each line is given as:

Opt ""  "lbound"    (bf $ \f x -> f{sLBound=x}) "show symbol table
after lambda lifting"

The \f x -> f bit is only there because setters are not first class
thingies. It's not quite as much additional syntax as you have in your
example, but its still not useful.



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