[Haskell-cafe] help with some code

gbwey9 gbwey9 at gmail.com
Sat Jul 12 03:52:49 UTC 2014

Hi Erik,

I'll take a look into it. Thanks for the help!


On Fri, Jul 11, 2014 at 11:39 PM, Erik Rantapaa <erantapaa at gmail.com> wrote:

> On Friday, July 11, 2014 10:01:38 AM UTC-5, gbwey9 wrote:
>> Hi Cafe,
>> I've got some code where a user can provide a filter to subscribe to a
>> particular type of event.  The events come in as xml and are parsed using
>> the toEvent method.
>> The code works fine but is repetitive since each event record potentially
>> has the information needed to parse the xml using the field names and
>> types.
>> So is there a way to get rid of the repetition and streamline the code?
>> Should I be using TH or lenses or something else entirely?
>> Here is the paste.
>> http://lpaste.net/107338
>> <http://www.google.com/url?q=http%3A%2F%2Flpaste.net%2F107338&sa=D&sntz=1&usg=AFQjCNGI_2_sqb7wOrLNKJBuTeDzCpLLBQ>
>> Thanks for any pointers!
>> Grant
> Regarding how the defining the toEvent instances can be simplified, have a
> look at the FromJSON type class works in the aeson package. One technique
> they use is to define FromJSON instances for even the primitive types (e.g.
> Int, String, DateTime, etc.) so that the FromJSON instances of records can
> be entirely type-directed removing the need to reference specific
> deserialization functions (e.g.  getint, getbool, etc.)
> One example of a package which uses aeson (of which there are many) is the
> github package:
> https://github.com/jwiegley/github/blob/master/Github/Data.hs
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