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

Peter Verswyvelen bugfact at gmail.com
Fri Jan 16 11:14:22 EST 2009

As far as I understand, record syntax and data accessor only give access to
the data, they don't provide alternate views / interpretations of the data,
something that Active Patterns or view patterns in Haskell do?
On Fri, Jan 16, 2009 at 4:27 PM, Henning Thielemann <
lemming at henning-thielemann.de> wrote:

> 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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