[Haskell-cafe] F# active patterns versus GHC's view

Henning Thielemann lemming at henning-thielemann.de
Fri Jan 16 10:27:53 EST 2009

On Fri, 16 Jan 2009, John Van Enk wrote:

> 2009/1/16 Peter Verswyvelen <bugfact at gmail.com>
>> [...]
>> After a while you decide that you need to change the Bla data type, maybe
>> give Dog more fields, maybe completely redesign it, maybe not exposing it,
>> but you want to keep existing code backwards compatible. With F# you can
>> write Active Patterns for the old Dog and Cat constructors, so all existing
>> code remains compatible. At least that is the way I understand it, but I
>> have not actually worked yet with Active Patterns, will do so soon :)
> You get something similar with the record syntax (though, probably still not
> quite as powerful as the active patterns):

... or use data-accessor package.

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