[Haskell-cafe] n00b question: defining datatype

[Kim-Ee Yeoh]

Consider

data Task = Task { title :: String, completed :: Bool, subtasks :: Maybe
[Task] }


Iain Barnett wrote:
> 
> Hi,
> I'm trying to get my head around datatypes, and wondering how I might
> define
> a simple  "Task" datatype in Haskell.
> data Task = Task { title :: String, completed :: Bool }
> Ok, that's straightforward, but sometimes tasks become a list of tasks
> themselves
> data Task = Task { title :: String, completed :: Bool, subtasks :: [Task]
> }
> But that's not really right, because obviously, some tasks don't have
> subtasks. So I try this:
> data Task = Task { title :: String, completed :: Bool } | TaskWithSubtasks
> {
> title :: String, completed :: Bool, subtasks :: [Task] }
> It's a bit more accurate, but it's repeating things, which is ok with a
> simple type. Could anyone suggest a better way to define this? If I was
> using C#, which I'm far more familiar with, I could overload the
> constructor
> and refer to the smaller constructor. Is there a way to do that in
> Haskell,
> or am I still thinking too OOP?
> Iain
> 
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> 
> 

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