[Haskell-beginners] trees on Haskell : Do I understand it right ?

[Roelof Wobben]

Hello,

Im looking for goofd online software to make the diagrams.
As soon as I find it . I will publish them on the ML.

Roelof

Joel Neely schreef op 1-3-2015 om 14:45:
> Roelof,
>
> Perhaps it would help for you to draw diagrams for the cases you're 
> working.
> If a leaf has nothing below it, and a node always has exactly three 
> things below it (the left child, the message, and the right child),
> what would your picture look like for 1, 2, and 3 nodes?
> And how would you write out constructor expressions that match those 
> shapes?
>
> Hope that helps,
> -jn-
>
>
> On Thu, Feb 26, 2015 at 12:32 PM, Roelof Wobben <r.wobben at home.nl 
> <mailto:r.wobben at home.nl>> wrote:
>
>     Oke,
>
>     I send it a second time but now in plain text.
>
>     So for 3 it will be like this :
>
>     Node = Node  (Node Leaf "msg1" Leaf) (Node Leaf "msg2") (Node 
>     "msg3" Leaf)  ???
>
>
>     Roelof
>
>
>
>>
>>
>>     Konstantine Rybnikov schreef op 26-2-2015 om 15:08:
>>>     In my second example you can see a minimal node with a message:
>>>
>>>     node = Node Leaf "msg" Leaf
>>>
>>>     Instead of either left or right Leaf you can put another value
>>>     of type MessageTree, for example:
>>>
>>>     node = Node Leaf "msg1" (Node Leaf "msg2" Leaf)
>>>
>>>     On Thu, Feb 26, 2015 at 4:01 PM, Roelof Wobben <r.wobben at home.nl
>>>     <mailto:r.wobben at home.nl>> wrote:
>>>
>>>         Oke,
>>>
>>>         So a leaf is a node which has no "branch"
>>>
>>>         I have made a exercise where I have to made the  logMessages.
>>>         Now I have to turn them into a tree
>>>
>>>         Where does the second entry goes then ?
>>>
>>>         Roelof
>>>
>>>
>>>         Konstantine Rybnikov schreef op 26-2-2015 om 14:56:
>>>>         Hi Roelof,
>>>>
>>>>         I think you misunderstood it.
>>>>
>>>>         There are two things here: types and values
>>>>         (value-constructors). They exist in different world, not
>>>>         touching each other.
>>>>
>>>>         In Haskell, you define a type as:
>>>>
>>>>         data <Type_Name> = <ValueConstructor_Name> <Type_Name>
>>>>         <Type_Name> <Type_Name>
>>>>
>>>>         You can create values as:
>>>>
>>>>         let varName = <ValueConstructor_Name> <Value> <Value> <Value>
>>>>
>>>>         You need to put <Value> of some type, not type name itself
>>>>         in place of those <Value>s.
>>>>
>>>>         So, with datatype you provided, you have two data-constructors:
>>>>
>>>>         Leaf
>>>>
>>>>         and
>>>>
>>>>         Node <val> <val> <val>
>>>>
>>>>         You can create a leaf:
>>>>
>>>>         let leaf = Leav
>>>>
>>>>         or a node:
>>>>
>>>>         let node = Node Leaf "msg" Leaf
>>>>
>>>>         You can see that Node is a data-constructor that takes 3
>>>>         values, not type-names as it's parameters.
>>>>
>>>>         Hope this helps.
>>>>
>>>>         On Thu, Feb 26, 2015 at 3:21 PM, Roelof Wobben
>>>>         <r.wobben at home.nl <mailto:r.wobben at home.nl>> wrote:
>>>>
>>>>             Hello,
>>>>
>>>>             Suppose we have this definition of a tree :
>>>>
>>>>             data MessageTree = Leaf
>>>>                              | Node MessageTree LogMessage MessageTree
>>>>               deriving (Show, Eq)
>>>>
>>>>             let Message  = LogMessage "E 1 this is a test error"
>>>>             let Message = LogMessage "e 2 this is the second test
>>>>             error "
>>>>
>>>>             As I understand it right I can make the first entry
>>>>             like this : first_entry = Node Messagetree  Message
>>>>             Messagetree
>>>>
>>>>             And the second one like this second_entry = Node
>>>>             Message Messagetree Message2 Messagetree ??
>>>>
>>>>             Roelof
>>>>
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>>>>
>>>>
>>>>
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>>>
>>>
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>>
>
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