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

[Joel Neely]

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> 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> 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> 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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-- 
Beauty of style and harmony and grace and good rhythm depend on simplicity.
- Plato
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