[Haskell-cafe] record update

[Henning Thielemann]

Jonathan Geddes schrieb:
> I know that record updates is a topic that has become a bit of a dead
> horse, but here I go anyway:
> 
> I find that most of the record updates I read and write take the form
> 
>> someUpdate :: MyRecord -> MyRecord
>> someUpdate myRecord = myRecord
>>     { field1 = f $ field1 myRecord
>>     , field2 = g $ field2 myRecord
>>     , field3 = h $ filed3 myRecord
>>     }
> 
> I find myself wishing I could write something more like
> 
>> someUpdate :: MyRecord -> MyRecord
>> someUpdate myRecord = myRecord
>>     { field1 => f
>>     , field2 => g
>>     , field3 => h
>>     }

data-accessor and similar packages may become your friends.

data-accessor allows you to write:

someUpdate =
   (field1 ^: f) .
   (field2 ^: g) .
   (field3 ^: h)