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@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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