[Haskell-cafe] Re: Non Empty List?

[Dan Weston]

Unless I'm missing something in your description, why not

   data Container a = Single a | Many a a [a]

Dan

GüŸnther Schmidt wrote:
> Hi Jake,
> 
> 
> Jake McArthur schrieb:
>> GüŸnther Schmidt wrote:
>>> data Container a = Single a | Many a [a]      
>>> but the problem above is that the data structure would allow to 
>>> construct a Many 5 [] :: Container Int.
>> I think you meant to do either
>>
>>     data Container a = Single a | Many a (Container a)
> 
> 
> 
> nope, I pretty much meant what I wrote above, the solution here would 
> mean deeply nested containers, since it's a recursive data structure.
> 
> I need a data structure as in my example without the [] being possible 
> to be empty.
> 
> It's quite possible that in order to achieve this I would need to split 
> this in 2 separate data declarations.
> 
> The idea behind this is that an "a" can "pocket" siblings, but only one 
> level deep and that an "a's" list of "pocketed/swallowed" siblings must 
> not be empty, because otherwise it would automatically be an "Single a".
> 
> Sorry, I really don't know how to put this better.
> 
> Günther
> 
>> or
>>
>>     data Container a = Container a [a]
>>
>> - Jake
> 
> 
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