How to cope with Haskell name space?

Question

I'm writing a `data` record to marshall a `JIRA` `JSON` object. The problem is, multiple objects have the same labels for name/value pairs. For example : (returned from curl and formatted) ``` {"expand":"schema,names" ,"startAt":0 ,"maxResults":2 ,"total":74 ,"issues":[ {"expand":"editmeta,renderedFields,transitions,changelog,operations" ,"id":"183614" ,"self":"https://10.64.16.44/rest/api/latest/issue/183614" ,"key":"BNAP-339" ,"fields":{"versions":[ {"self":"https://10.64.16.44/rest/api/2/version/28240" ,"id":"28240" ,"name":"2012-12-07" ,"archived":false ,"released":false } ] ,"status":{"self":"https://10.64.16.44/rest/api/2/status/1" ,"description":"The issue is open and ready for the assignee to start work on it." ,"iconUrl":"https://10.64.16.44/images/icons/status_open.gif" ,"name":"Open" ,"id":"1" } ,"description":"Do Re Mi Fa" ,"resolution":null } } ] ``` when I construct the problematic corresponding Haskell `data` records I get: ``` data Issue = Issue {expand :: String ,id :…

Accepted Answer

I solve this in protocol buffers by putting things like `Issue` and `Version` in separate files in the same hierarchy.

Haskell only uses separate modules to control namespaces, so this is the orthodox solution.

Much much fancier: use type classes to define available name:

```
class Has'self a b | a -> bwhere
   get'self :: a -> b
   set'self :: b -> a -> b

instance Has'self Issue String where ...
instance Has'self Version String where ....
```

EDIT: The comments below remind me to give more verbose advice. Do not use Has'self like solutions -- those that have gone that road report it gets ugly. I can vouch for the path of separate modules.

PS: Perhaps you can use the lens library for your fields!

How to cope with Haskell name space?

Solution

Problem