So, as the simplest solution -- you need to read file, split it by lines (convert it to list of lines), for each line check it for validity and return some result, which would have type, for example Either String LogMsg , where Left String indicates error, and other one is Right LogMsg, with this type: data LogLevel = LevelW | LevelE | LevelI data LogMsg = LogMsg LogLevel Int String Then you would filter all rights to output to new logfile, and filter all lefts to do whatever you wanted to do with them (you didn't specify this, I think). Does this look clear? Ask if you have more questions! 22 лют. 2015 18:24, користувач "Roelof Wobben" написав:

Sorry,

I stand for Info E stands for Error W stands for Warning.

The clause Im talking about is that the log message must be the format char Int [char] so like this: W 10 this is a warning All the sentences that are not of this format , like for example this one: W this is a false warning , must have another output. That's is also true when the first Char is not a W, E or I.

When it's a W , E, or I then the char must be converted to the word Warning, Error or Info.

I hope it's clear now what I want.

Roelof

Konstantine Rybnikov schreef op 22-2-2015 om 16:17:

Hi Roelof,

You forgot to explain what are those fields you are talking about, and what are I/E/W . Also what are those clauses you are talking about?

Cheers. 21 лют. 2015 09:03, користувач "Roelof Wobben" написав:

...

Hello,

Im busy with a programm which translates log files to another format. I also have to look if the lines in the old one have the rigtht format.

Schould I check the format and also if another field contains a I, E or W. Or schould I do the checking in one clause and make another case on the rest ?

Roelof

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As Alex mentioned, isValid returns Bool, while type for putStrLn is `String -> IO ()`. So, in order to print something of type Bool, you need to first convert it to String. For example, via a function `show`: putStrLn (show True) As Alex mentioned, there's a `print` function, which does exactly this: print x = putStrLn (show x) You can use it. On Mon, Feb 23, 2015 at 7:19 PM, Roelof Wobben wrote:

And when Im trying this:

{-# OPTIONS_GHC -Wall #-}

module LogAnalysis where

import Log; import Data.Char (isLetter, isDigit)

isValid :: String -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False

-- | The main entry point. main :: IO () main = do putStrLn $ isValid "I 4764 He trusts to you to set them free,"

I see this error message :

src/LogAnalysis.hs@19:16-19:67 Couldn't match type Bool with [Char] Expected type: String Actual type: Bool … In the second argument of ‘($)’, namely ‘isValid "I 4764 He trusts to you to set them free,"’ In a stmt of a 'do' block: putStrLn $ isValid "I 4764 He trusts to you to set them free,"

Roelof

Roelof Wobben schreef op 23-2-2015 om 17:19:

I tried it another way more like explained on this page : http://www.seas.upenn.edu/~cis194/spring13/lectures/02-ADTs.html

so I tried this :

parseMessage :: [Char] -> [Char] parseMessage s case Errornumber of IsDigit Errornumber -> "Geldige string" otherwise -> "Ongeldige string" where Error = s words Errornumber = Error(ErrorNumber _ _ ) Errorcode = Error(_ Errorcode _ )

but now I cannot use where :(

Roelof

Roelof Wobben schreef op 23-2-2015 om 16:10:

Oke,

Then I make there a mistake,

What I try to do is to send the file to parseMessage and let IsValid check if it´s have the right format.

Then after the where I try to check if the function isValid returns true or false.

Roelof

Konstantine Rybnikov schreef op 23-2-2015 om 16:03:

Roelof,

You defined isValid function in the upper-scope first, and then you defined a symbol (variable) that re-wrote that name to something different (string "Geldige string"). That's why you get an error saying it doesn't expect arguments.

My suggestion is to rename second isValid.

Good luck.

On Mon, Feb 23, 2015 at 4:50 PM, Roelof Wobben wrote:

...

Chaddaï Fouché schreef op 23-2-2015 om 13:20:

Note that Roelof is doing the CIS 194 Homework http://www.seas.upenn.edu/~cis194/fall14/hw/03-ADTs.pdf (the older version of fall2014, not the one currently running). This is much clearer than Roelof's description, and gives among other information an algebraic datatype to represent log messages.

-- Jedaï

Correct and Im trying to do exercise 1 of Week 2,

I have tried this solution :

-- | Main entry point to the application. {-# OPTIONS_GHC -Wall #-}

module LogAnalysis where

import Log; import Data.Char (isLetter, isDigit)

isValid :: [Char] -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False

parseMessage :: [Char] -> [Char] parseMessage s = isValid s where isValid = "Geldige string" _ = "Ongeldige string"

-- | The main entry point. main :: IO () main = do putStrLn $ parseMessage "I 4764 He trusts to you to set them free,"

but I see this error message :

src/LogAnalysis.hs@16:18-16:27 Couldn't match expected type ‘[Char] -> [Char]’ with actual type [Char] The function isValid is applied to one argument, but its type [Char] has none … In the expression: isValid s In an equation for ‘parseMessage’: parseMessage s = isValid s where isValid = "Geldige string" _ = "Ongeldige string"

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Constructors with names like 'Unknown' are a code smell, IMO. I'd just define the data type like this: data LogMessage = LogMessage MessageType TimeStamp String and use `Either String LogMessage` in contexts where parsing can fail: parseLogEntry :: String -> Either String LogMesage parseLogEntry str | isValid str = Right $ mkLogMessage str | otherwise = Left $ "Poorly-formatted log entry: " ++ str As for implementing mkLogMessage: you already know how to unpack the parts of a log message with `words` and pattern matching. After that it's just a matter of type-casting everything correctly and passing it to the `LogMessage` constructor. On Mon, Feb 23, 2015 at 10:14 AM, Roelof Wobben wrote:

Thanks,

This works :

-- | Main entry point to the application. {-# OPTIONS_GHC -Wall #-}

module LogAnalysis where

import Data.Char (isLetter, isDigit)

isValid :: String -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False

-- | The main entry point. main :: IO () main = do putStrLn $ ( show (isValid "I 656 He trusts to you to set them free,"))

Now I have to ty to find out how I can check if a has the contents of I/W/E and how to make the right output (Error/Warning/Info 22) " Text" ) and then make it work with this datatype :

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

Roelof

Konstantine Rybnikov schreef op 23-2-2015 om 18:49:

As Alex mentioned, isValid returns Bool, while type for putStrLn is `String -> IO ()`. So, in order to print something of type Bool, you need to first convert it to String. For example, via a function `show`:

putStrLn (show True)

As Alex mentioned, there's a `print` function, which does exactly this:

print x = putStrLn (show x)

You can use it.

On Mon, Feb 23, 2015 at 7:19 PM, Roelof Wobben wrote:

...

And when Im trying this:

{-# OPTIONS_GHC -Wall #-}

module LogAnalysis where

import Log; import Data.Char (isLetter, isDigit)

isValid :: String -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False

-- | The main entry point. main :: IO () main = do putStrLn $ isValid "I 4764 He trusts to you to set them free,"

I see this error message :

src/LogAnalysis.hs@19:16-19:67 Couldn't match type Bool with [Char] Expected type: String Actual type: Bool … In the second argument of ‘($)’, namely ‘isValid "I 4764 He trusts to you to set them free,"’ In a stmt of a 'do' block: putStrLn $ isValid "I 4764 He trusts to you to set them free,"

Roelof

Roelof Wobben schreef op 23-2-2015 om 17:19:

I tried it another way more like explained on this page : http://www.seas.upenn.edu/~cis194/spring13/lectures/02-ADTs.html

so I tried this :

parseMessage :: [Char] -> [Char] parseMessage s case Errornumber of IsDigit Errornumber -> "Geldige string" otherwise -> "Ongeldige string" where Error = s words Errornumber = Error(ErrorNumber _ _ ) Errorcode = Error(_ Errorcode _ )

but now I cannot use where :(

Roelof

Roelof Wobben schreef op 23-2-2015 om 16:10:

Oke,

Then I make there a mistake,

What I try to do is to send the file to parseMessage and let IsValid check if it´s have the right format.

Then after the where I try to check if the function isValid returns true or false.

Roelof

Konstantine Rybnikov schreef op 23-2-2015 om 16:03:

Roelof,

You defined isValid function in the upper-scope first, and then you defined a symbol (variable) that re-wrote that name to something different (string "Geldige string"). That's why you get an error saying it doesn't expect arguments.

My suggestion is to rename second isValid.

Good luck.

On Mon, Feb 23, 2015 at 4:50 PM, Roelof Wobben wrote:

...

Chaddaï Fouché schreef op 23-2-2015 om 13:20:

Note that Roelof is doing the CIS 194 Homework http://www.seas.upenn.edu/~cis194/fall14/hw/03-ADTs.pdf (the older version of fall2014, not the one currently running). This is much clearer than Roelof's description, and gives among other information an algebraic datatype to represent log messages.

-- Jedaï

Correct and Im trying to do exercise 1 of Week 2,

I have tried this solution :

-- | Main entry point to the application. {-# OPTIONS_GHC -Wall #-}

module LogAnalysis where

import Log; import Data.Char (isLetter, isDigit)

isValid :: [Char] -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False

parseMessage :: [Char] -> [Char] parseMessage s = isValid s where isValid = "Geldige string" _ = "Ongeldige string"

-- | The main entry point. main :: IO () main = do putStrLn $ parseMessage "I 4764 He trusts to you to set them free,"

but I see this error message :

src/LogAnalysis.hs@16:18-16:27 Couldn't match expected type ‘[Char] -> [Char]’ with actual type [Char] The function isValid is applied to one argument, but its type [Char] has none … In the expression: isValid s In an equation for ‘parseMessage’: parseMessage s = isValid s where isValid = "Geldige string" _ = "Ongeldige string"

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You can pattern match on string literals: parseMessage :: String -> String parseMessage s = go (words s) where go ("I":_:_) = "Info" go _ = "false" You don't need to call it "go2", btw. Functions in where-blocks don't leak into the global scope, so there's no conflict with the `go` in your other function. On Mon, Feb 23, 2015 at 12:15 PM, Roelof Wobben wrote:

Sorry ,

I cannot change that function. I have to use it,

But I think I found a solution for a step earlier,

To parse a line and change it to another line which will be a member of LogMessage :

-- | Main entry point to the application. {-# OPTIONS_GHC -Wall #-}

module LogAnalysis where

import Data.Char (isLetter, isDigit)

isValid :: String -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False

parseMessage :: String -> String parseMessage s = go2 (words s) where go2 (a:_:_) = case a of "I" -> "Info " _ -> "False"

go2 _ = "false"

-- | The main entry point. main :: IO () main = do putStrLn $ parseMessage "I 656 He trusts to you to set them free,"

But I feels wierd, to use first a pattern matching and later do a case of. Is this a good way or are there better ways,

Roelfo

Alex Hammel schreef op 23-2-2015 om 21:01:

Constructors with names like 'Unknown' are a code smell, IMO. I'd just define the data type like this:

data LogMessage = LogMessage MessageType TimeStamp String

and use `Either String LogMessage` in contexts where parsing can fail:

parseLogEntry :: String -> Either String LogMesage parseLogEntry str | isValid str = Right $ mkLogMessage str | otherwise = Left $ "Poorly-formatted log entry: " ++ str

As for implementing mkLogMessage: you already know how to unpack the parts of a log message with `words` and pattern matching. After that it's just a matter of type-casting everything correctly and passing it to the `LogMessage` constructor.

On Mon, Feb 23, 2015 at 10:14 AM, Roelof Wobben wrote:

...

Thanks,

This works :

-- | Main entry point to the application. {-# OPTIONS_GHC -Wall #-}

module LogAnalysis where

import Data.Char (isLetter, isDigit)

isValid :: String -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False

-- | The main entry point. main :: IO () main = do putStrLn $ ( show (isValid "I 656 He trusts to you to set them free,"))

Now I have to ty to find out how I can check if a has the contents of I/W/E and how to make the right output (Error/Warning/Info 22) " Text" ) and then make it work with this datatype :

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

Roelof

Konstantine Rybnikov schreef op 23-2-2015 om 18:49:

As Alex mentioned, isValid returns Bool, while type for putStrLn is `String -> IO ()`. So, in order to print something of type Bool, you need to first convert it to String. For example, via a function `show`:

putStrLn (show True)

As Alex mentioned, there's a `print` function, which does exactly this:

print x = putStrLn (show x)

You can use it.

On Mon, Feb 23, 2015 at 7:19 PM, Roelof Wobben wrote:

...

And when Im trying this:

{-# OPTIONS_GHC -Wall #-}

module LogAnalysis where

import Log; import Data.Char (isLetter, isDigit)

isValid :: String -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False

-- | The main entry point. main :: IO () main = do putStrLn $ isValid "I 4764 He trusts to you to set them free,"

I see this error message :

src/LogAnalysis.hs@19:16-19:67 Couldn't match type Bool with [Char] Expected type: String Actual type: Bool … In the second argument of ‘($)’, namely ‘isValid "I 4764 He trusts to you to set them free,"’ In a stmt of a 'do' block: putStrLn $ isValid "I 4764 He trusts to you to set them free,"

Roelof

Roelof Wobben schreef op 23-2-2015 om 17:19:

I tried it another way more like explained on this page : http://www.seas.upenn.edu/~cis194/spring13/lectures/02-ADTs.html

so I tried this :

parseMessage :: [Char] -> [Char] parseMessage s case Errornumber of IsDigit Errornumber -> "Geldige string" otherwise -> "Ongeldige string" where Error = s words Errornumber = Error(ErrorNumber _ _ ) Errorcode = Error(_ Errorcode _ )

but now I cannot use where :(

Roelof

Roelof Wobben schreef op 23-2-2015 om 16:10:

Oke,

Then I make there a mistake,

What I try to do is to send the file to parseMessage and let IsValid check if it´s have the right format.

Then after the where I try to check if the function isValid returns true or false.

Roelof

Konstantine Rybnikov schreef op 23-2-2015 om 16:03:

Roelof,

You defined isValid function in the upper-scope first, and then you defined a symbol (variable) that re-wrote that name to something different (string "Geldige string"). That's why you get an error saying it doesn't expect arguments.

My suggestion is to rename second isValid.

Good luck.

On Mon, Feb 23, 2015 at 4:50 PM, Roelof Wobben wrote:

...

Chaddaï Fouché schreef op 23-2-2015 om 13:20:

Note that Roelof is doing the CIS 194 Homework http://www.seas.upenn.edu/~cis194/fall14/hw/03-ADTs.pdf (the older version of fall2014, not the one currently running). This is much clearer than Roelof's description, and gives among other information an algebraic datatype to represent log messages.

-- Jedaï

Correct and Im trying to do exercise 1 of Week 2,

I have tried this solution :

-- | Main entry point to the application. {-# OPTIONS_GHC -Wall #-}

module LogAnalysis where

import Log; import Data.Char (isLetter, isDigit)

isValid :: [Char] -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False

parseMessage :: [Char] -> [Char] parseMessage s = isValid s where isValid = "Geldige string" _ = "Ongeldige string"

-- | The main entry point. main :: IO () main = do putStrLn $ parseMessage "I 4764 He trusts to you to set them free,"

but I see this error message :

src/LogAnalysis.hs@16:18-16:27 Couldn't match expected type ‘[Char] -> [Char]’ with actual type [Char] The function isValid is applied to one argument, but its type [Char] has none … In the expression: isValid s In an equation for ‘parseMessage’: parseMessage s = isValid s where isValid = "Geldige string" _ = "Ongeldige string"

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On 24/02/2015, at 5:19 am, Roelof Wobben wrote:

I tried it another way more like explained on this page : http://www.seas.upenn.edu/~cis194/spring13/lectures/02-ADTs.html

so I tried this :

parseMessage :: [Char] -> [Char] parseMessage s case Errornumber of IsDigit Errornumber -> "Geldige string" otherwise -> "Ongeldige string" where Error = s words Errornumber = Error(ErrorNumber _ _ ) Errorcode = Error(_ Errorcode _ )

but now I cannot use where :(

That's not your problem. IsDigit ErrorNumber is not a pattern. parseMessage s = if isDigit errorNumber then "Geldige string" else "Ongelidige string" where errorNumber = ??? is OK. Now I cannot make sense of Error = s words identifiers beginning with capital letters are used for - module names - type constructors - data constructors You want a variable here, so it must begin with a lower case letter. s words treats a string s as a function and applies it to the function words as argument: s(words). But that does not type check. You mean words s. The result of words s, whatever else it may be, is not an error. Errornumber = Error(ErrorNumber _ _) In the form "expr where pattern = expr", the thing after the equal sign must be an expression. But Error(ErrorNumber _ _) is not an expression. "_" is a PATTERN (= I do not care what goes here) but never an EXPRESSION (because what value would it have?).

Thanks, I rewrote it like this : parseMessage :: String -> LogMessage parseMessage s = case words s of ("I":time:text) -> LogMessage Info (read time) (unwords text) ("W":time:text) -> LogMessage Warning (read time) (unwords text) ("E":errorcode:time:text) -> LogMessage Error (read errorcode) (read time) (unwords text) _ -> Unknown "This is not in the right format" The only thing Im facing now It the Error part. Messagetype has this signature : data MessageType = Info | Warning | Error Int deriving (Show, Eq) So Error has a Messagatype which contains 2 things. but because of the use of words I looks like this I think [ "E", 46, 23456 , "This", "is", "a", "error". ] Can I somehow use unwords here to to make the Messagetype work. Roelof Richard A. O'Keefe schreef op 24-2-2015 om 2:01:

On 24/02/2015, at 3:50 am, Roelof Wobben wrote:

...

isValid :: [Char] -> Bool isValid s = go (words s) where go ([a]:b:_) = isLetter a && all isDigit b go _ = False My attention was caught by the remarkably unhelpful name "go". What goes? Where does it go? What does going mean?

This is a good time to use a 'case':

isValid s = case words s of [a]:b:_ -> isLetter a && all isDigit b _ -> False

...

parseMessage :: [Char] -> [Char]

parseMessage s = isValid s where isValid = "Geldige string" _ = "Ongeldige string" In the first line of this function, you are calling isValid with an argument. But you are defining isValid to be a string!

parseMessage s = if isValid s then "Geldige string" else "Ongeldige string"

"parseMessage: is a bad name because the purpose of the function is *NOT* to break the message into parts and deliver those parts but to CHECK or VALIDATE or CLASSIFY the message.

The code

import Data.Char

isValid s = case words s of [a]:b:_ -> isLetter a && all isDigit b _ -> False

parseMessage s = if isValid s then "Geldige string" else "Ongeldige string"

main = putStrLn $ parseMessage "I 4764 He trusts to you to set them free,"

compiles without warnings and produces the result I think you want.