On Sat, Feb 28, 2015 at 5:07 AM, Roelof Wobben wrote:

That part I understand .

it's more how I do it here :

Lets say I have this :

data MessageType = Info | Warning | Error Int deriving (Show, Eq)

type TimeStamp = Int

data LogMessage = LogMessage MessageType TimeStamp String | Unknown String deriving (Show, Eq)

data MessageTree = Leaf | Node MessageTree LogMessage MessageTree deriving (Show, Eq)

Now I have to put all the LogMessages in a binary tree. with this signature : insert :: LogMessage -> MessageTree -> MessageTree

I think I need recursion here but I still not see how I can make the clauses. Normally you can say somethig like this [] -> 0 or 1 -> but here it seems to be all seperate logMessages

Whether you need recursion or not depends on where you're to insert the message. For instance, you could turn them into a list with: insert message tree = Node tree message Leaf Try drawing a few pictures of what that produces, and you'll see why it's probably not what you want. You should be able to tell by looking at the MessageTree type that you have two cases: one where you're passed something matching a Node, and one where you're passed something that's just a Leaf. The latter can't be recursive, so it's going to terminate any recursion. Following the advice given to you for the Hanoi problem, try writing it first. Then all you have to do is figure out how to handle the case where you're given a Node instead of a Leaf. Figuring out where in the MessageTree you want to insert the Logmessage will probably be required to do that.

You're missing an argument to insert, assuming that it is indeed there, consider this: insert msg tree = tree' where tree' = undefined -- Take a LogMessage (msg) and a MessageTree (tree) -- and return a new MessageTree (tree') Therefore, the result of insert in your case, i.e. "MessageTree Leaf" should be of type MessageTree. And thus, we get MessageTree Leaf :: MessageTree -- Takes a (Leaf :: LogMessage) and produces a MessageTree which implies, MessageTree :: LogMessage -> MessageTree -- A Data constructor Obviously no such data constructor exists. A data constructor of this type would exist only if you wrote something like: data MessageTree = MessageTree LogMessage | ... which would not make sense. On 28 February 2015 at 19:09, Roelof Wobben wrote:

I tried this :

insert :: LogMessage -> MessageTree -> MessageTree insert s = case words s of (_:_: "This is not the right format") -> MessageTree Leaf _ -> MessageTree Node LogMessage Leaf

But I see this errormessages which I do not understand :

src/LogAnalysis.hs@38:49-38:60 Not in scope: data constructor MessageTree src/LogAnalysis.hs@39:49-39:60 Not in scope: data constructor MessageTree

Mike Meyer schreef op 28-2-2015 om 12:17:

On Sat, Feb 28, 2015 at 5:07 AM, Roelof Wobben wrote:

...

That part I understand .

it's more how I do it here :

Lets say I have this :

data MessageType = Info | Warning | Error Int deriving (Show, Eq)

type TimeStamp = Int

data LogMessage = LogMessage MessageType TimeStamp String | Unknown String deriving (Show, Eq)

data MessageTree = Leaf | Node MessageTree LogMessage MessageTree deriving (Show, Eq)

Now I have to put all the LogMessages in a binary tree. with this signature : insert :: LogMessage -> MessageTree -> MessageTree

I think I need recursion here but I still not see how I can make the clauses. Normally you can say somethig like this [] -> 0 or 1 -> but here it seems to be all seperate logMessages

Whether you need recursion or not depends on where you're to insert the message. For instance, you could turn them into a list with:

insert message tree = Node tree message Leaf

Try drawing a few pictures of what that produces, and you'll see why it's probably not what you want.

You should be able to tell by looking at the MessageTree type that you have two cases: one where you're passed something matching a Node, and one where you're passed something that's just a Leaf. The latter can't be recursive, so it's going to terminate any recursion. Following the advice given to you for the Hanoi problem, try writing it first.

Then all you have to do is figure out how to handle the case where you're given a Node instead of a Leaf. Figuring out where in the MessageTree you want to insert the Logmessage will probably be required to do that.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

-- Regards Sumit Sahrawat

Don't worry. Keep these points in mind and re-read my previous mail. Regarding data vs. type constructors. 1) Leaf :: MessageTree (Leaf is a MessageTree) 2) MessageTree is a type constructor (takes types and gives new types) 3) Node is a data constructor (takes values and gives a new MessageTree) Regarding insertion. 1) The "insert" function takes a message and tree, and returns a tree with that message inserted into it 2) We absolutely have to provide it a tree 3) If we insert an invalid message in the tree, it does not get added. Then we get ..... the same tree back. If you still cannot see a problem in your code, ask yourself the following: 1) What type does the output of insert (MessageTree Leaf) have, and what type should it have 2) What happens if we insert an invalid string in a non-empty tree (according to your code) Don't forget to re-read the previous mail. Hope this drives the point home. On 28 February 2015 at 22:59, Roelof Wobben wrote:

Sorry,

But I do not understand what you mean.

What I try to do is this

If you have a LogMessage which contains " This is not the right format " then the LogMessage is not inserted in the tree. Every other message are inserted in the tree.

So that is why I make a MessageTree with only one Leaf.

Roelof

Sumit Sahrawat, Maths & Computing, IIT (BHU) schreef op 28-2-2015 om 16:08:

You're missing an argument to insert, assuming that it is indeed there, consider this:

insert msg tree = tree' where tree' = undefined -- Take a LogMessage (msg) and a MessageTree (tree) -- and return a new MessageTree (tree')

Therefore, the result of insert in your case, i.e. "MessageTree Leaf" should be of type MessageTree. And thus, we get

MessageTree Leaf :: MessageTree -- Takes a (Leaf :: LogMessage) and produces a MessageTree

which implies,

MessageTree :: LogMessage -> MessageTree -- A Data constructor

Obviously no such data constructor exists. A data constructor of this type would exist only if you wrote something like:

data MessageTree = MessageTree LogMessage | ...

which would not make sense.

On 28 February 2015 at 19:09, Roelof Wobben wrote:

...

I tried this :

insert :: LogMessage -> MessageTree -> MessageTree insert s = case words s of (_:_: "This is not the right format") -> MessageTree Leaf _ -> MessageTree Node LogMessage Leaf

But I see this errormessages which I do not understand :

src/LogAnalysis.hs@38:49-38:60 Not in scope: data constructor MessageTree src/LogAnalysis.hs@39:49-39:60 Not in scope: data constructor MessageTree

Mike Meyer schreef op 28-2-2015 om 12:17:

On Sat, Feb 28, 2015 at 5:07 AM, Roelof Wobben wrote:

...

That part I understand .

it's more how I do it here :

Lets say I have this :

data MessageType = Info | Warning | Error Int deriving (Show, Eq)

type TimeStamp = Int

data LogMessage = LogMessage MessageType TimeStamp String | Unknown String deriving (Show, Eq)

data MessageTree = Leaf | Node MessageTree LogMessage MessageTree deriving (Show, Eq)

Now I have to put all the LogMessages in a binary tree. with this signature : insert :: LogMessage -> MessageTree -> MessageTree

I think I need recursion here but I still not see how I can make the clauses. Normally you can say somethig like this [] -> 0 or 1 -> but here it seems to be all seperate logMessages

Whether you need recursion or not depends on where you're to insert the message. For instance, you could turn them into a list with:

insert message tree = Node tree message Leaf

Try drawing a few pictures of what that produces, and you'll see why it's probably not what you want.

You should be able to tell by looking at the MessageTree type that you have two cases: one where you're passed something matching a Node, and one where you're passed something that's just a Leaf. The latter can't be recursive, so it's going to terminate any recursion. Following the advice given to you for the Hanoi problem, try writing it first.

Then all you have to do is figure out how to handle the case where you're given a Node instead of a Leaf. Figuring out where in the MessageTree you want to insert the Logmessage will probably be required to do that.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

-- Regards

Sumit Sahrawat

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

-- Regards Sumit Sahrawat

Richard A. O'Keefe schreef op 2-3-2015 om 0:59:

On 1/03/2015, at 11:17 pm, Roelof Wobben wrote:

...

Now I have to find out how I can test if the LogMessage has the text "this is not the right format" in it.

Well, the Haskell libraries include regular expression support. At an elementary level, you can always do

is_prefix_of :: Eq x => [x] -> [x] -> Bool is_prefix_of (x:xs) (y:ys) = x == y && is_prefix_of xs ys is_prefix_of (x:xs) [] = False is_prefix_of [] _ = True

is_infix_of :: Eq x => [x] -> [x] -> Bool

is_infix_of xs ys = xs `is_prefix_of` ys || (not (null ys) && xs `is_infix_of` tail ys)

"this is not the right format" `is_infix_of` aLogMessage

But it would be better if your LogMessage were not a string but something structured where you did not have to go looking for that text because you KNEW where to look for it.

I know where to look. A LogMessage looks like this : data LogMessage = LogMessage MessageType TimeStamp String | Unknown String deriving (Show, Eq) So if it's Unknown with a string then it will not be inserted into the MessageTree The only thing I have to find out if LogMessage contains this. Roelof

On 1/03/2015, at 2:39 am, Roelof Wobben wrote:

I tried this :

insert :: LogMessage -> MessageTree -> MessageTree insert s = case words s of (_:_: "This is not the right format") -> MessageTree Leaf _ -> MessageTree Node LogMessage Leaf

This makes no sense. You have declared that insert takes a LogMessage argument and a MessageTree argument and returns a MessageTree result. Then your code DOES NOT ACCEPT A MESSAGETREE ARGUMENT! You want to have insert logmsg msgtree = and the case analysis should be on the message tree, not the log message. src/LogAnalysis.hs@38:49-38:60

Not in scope: data constructor MessageTree src/LogAnalysis.hs@39:49-39:60 Not in scope: data constructor MessageTree

The compiler is telling you, as clearly as it knows how, that you DO NOT HAVE ANY CONSTRUCTOR FUNCTION called "MessageTree". The constructor functions are >> Leaf << and >> Node <<. MessageTree is a *TYPE NAME*. I am about to be offensive. I do not want to be offensive. I want to be helpful. I believe this question needs to be asked. But there is a real risk that I will offend you. Here goes. Is there *any* programming language you know how to use? The reason that I ask is that the problems you keep having aren't really Haskell problems. They are general programming problems: - declaring a name as one kind of thing and using it as if it were another - declaring a function (like 'insert' or 'Node') to have n arguments but trying to define or call it with m arguments where m ~= n. - not starting with a description of your problem - not having a clue what to do when the compiler tells you something. (It's OK not to understand a compiler message. But you should get *some* clue from it, like where exactly to look, and you should be able to try to vary the program to see how the message changes.) I honestly feel that the difficulties you are reporting here aren't really Haskell difficulties, just as the difficulties you were reporting in the Erlang mailing list weren't really Erlang difficulties, but in both cases, something much more fundamental. To restate my possibly offensive question again: Have you ever had a course of instruction in the use of any programming language face to face with a competent teacher? Again, I'm trying to be helpful here. If you run into a problem and can get help within *minutes*, and have someone sit down beside you at the keyboard and *show* you how to find out what a compiler message might mean and what to do about it, you can learn very quickly. If you have to wait hours for responses, you are obviously going to learn much more slowly. I sometimes ask my students: "What's the point of coming here? Why not just buy a textbook?" Sadly, they sometimes do not know the answer. It's "You can ask ME questions, and each other." It is clear that you are working at trying to learn Haskell. It is SMART of you to ask questions. It's just that there are these really basic issues where I think you could learn a lot faster with face-to-face help.