<div dir="ltr">You can pattern match on string literals:<br><br>parseMessage :: String -> String<br>parseMessage s = go (words s)<br> where<br> go ("I":_:_) = "Info"<br> go _ = "false"<br><br><br>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.<br><br></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Feb 23, 2015 at 12:15 PM, Roelof Wobben <span dir="ltr"><<a href="mailto:r.wobben@home.nl" target="_blank">r.wobben@home.nl</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>Sorry ,<br>
<br>
I cannot change that function. I have to use it, <br>
<br>
But I think I found a solution for a step earlier, <br>
<br>
To parse a line and change it to another line which will be a
member of LogMessage : <br><span class="">
<br>
-- | Main entry point to the application.<br>
{-# OPTIONS_GHC -Wall #-}<br>
<br>
module LogAnalysis where<br>
<br>
import Data.Char (isLetter, isDigit)<br>
<br>
isValid :: String -> Bool<br>
isValid s = go (words s)<br>
where<br>
go ([a]:b:_) = isLetter a && all isDigit b<br>
go _ = False<br>
<br></span>
parseMessage :: String -> String<br>
parseMessage s = go2 (words s) <br>
where <br>
go2 (a:_:_) = case a of<br>
"I" -> "Info "<br>
_ -> "False"<br>
<br>
go2 _ = "false"<span class=""><br>
<br>
<br>
-- | The main entry point.<br>
main :: IO ()<br>
main = do<br></span>
putStrLn $ parseMessage "I 656 He trusts to you to set them
free,"<br>
<br>
<br>
<br>
But I feels wierd, to use first a pattern matching and later do a
case of.<br>
Is this a good way or are there better ways, <br>
<br>
Roelfo<br>
<br>
<br>
<br>
Alex Hammel schreef op 23-2-2015 om 21:01:<br>
</div><div><div class="h5">
<blockquote type="cite">
<div dir="ltr">Constructors with names like 'Unknown' are a code
smell, IMO. I'd just define the data type like this:<br>
<br>
data LogMessage = LogMessage MessageType TimeStamp String<br>
<br>
and use `Either String LogMessage` in contexts where parsing can
fail:<br>
<br>
parseLogEntry :: String -> Either String LogMesage<br>
parseLogEntry str<br>
| isValid str = Right $ mkLogMessage str<br>
| otherwise = Left $ "Poorly-formatted log entry: " ++ str<br>
<br>
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.<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Feb 23, 2015 at 10:14 AM,
Roelof Wobben <span dir="ltr"><<a href="mailto:r.wobben@home.nl" target="_blank">r.wobben@home.nl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>Thanks, <br>
<br>
This works : <br>
<span> <br>
-- | Main entry point to the application.<br>
{-# OPTIONS_GHC -Wall #-}<br>
<br>
module LogAnalysis where<br>
<br>
</span><span> import Data.Char (isLetter,
isDigit)<br>
<br>
isValid :: String -> Bool<br>
isValid s = go (words s)<br>
where<br>
go ([a]:b:_) = isLetter a && all isDigit
b<br>
go _ = False<br>
<br>
<br>
-- | The main entry point.<br>
main :: IO ()<br>
main = do<br>
</span> putStrLn $ ( show (isValid "I 656 He trusts
to you to set them free,"))<br>
<br>
<br>
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" ) <br>
and then make it work with this datatype : <br>
<br>
data LogMessage = LogMessage MessageType TimeStamp
String<br>
| Unknown String<br>
deriving (Show, Eq)<br>
<br>
Roelof<br>
<br>
Konstantine Rybnikov schreef op 23-2-2015 om 18:49:<br>
</div>
<div>
<div>
<blockquote type="cite">
<div dir="ltr">
<div>
<div>
<div>
<div>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`:<br>
<br>
</div>
putStrLn (show True)<br>
<br>
</div>
As Alex mentioned, there's a `print` function,
which does exactly this:<br>
<br>
</div>
print x = putStrLn (show x)<br>
<br>
</div>
You can use it.<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Feb 23, 2015 at
7:19 PM, Roelof Wobben <span dir="ltr"><<a href="mailto:r.wobben@home.nl" target="_blank">r.wobben@home.nl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>And when Im trying this: <br>
<span> <br>
{-# OPTIONS_GHC -Wall #-}<br>
<br>
module LogAnalysis where<br>
<br>
import Log;<br>
import Data.Char (isLetter, isDigit)<br>
<br>
</span> isValid :: String -> Bool<span><br>
isValid s = go (words s)<br>
where<br>
go ([a]:b:_) = isLetter a
&& all isDigit b<br>
go _ = False<br>
<br>
<br>
</span><span> -- | The main entry point.<br>
main :: IO ()<br>
main = do<br>
</span> putStrLn $ isValid "I 4764 He
trusts to you to set them free,"<span><br>
<br>
<br>
I see this error message : <br>
<br>
</span>
<div>src/LogAnalysis.hs@19:16-19:67 </div>
<div><span>Couldn't match type </span>
<div style="font-size:14px"><span>Bool</span></div>
<span> with </span>
<div style="font-size:14px">[<span>Char</span>]</div>
<span> Expected type: String Actual
type: Bool</span><span title="Click to
show/hide extra information"> …</span><span style="display:inline"> 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,"<br>
<br>
Roelof<br>
<br>
</span></div>
<br>
<br>
<br>
<br>
Roelof Wobben schreef op 23-2-2015 om
17:19:<br>
</div>
<div>
<div>
<blockquote type="cite">
<div>I tried it another way more like
explained on this page : <a href="http://www.seas.upenn.edu/%7Ecis194/spring13/lectures/02-ADTs.html" target="_blank">http://www.seas.upenn.edu/~cis194/spring13/lectures/02-ADTs.html</a><br>
<br>
so I tried this : <br>
<br>
parseMessage :: [Char] -> [Char]<br>
parseMessage s<br>
case Errornumber of <br>
IsDigit Errornumber ->
"Geldige string"<br>
otherwise ->
"Ongeldige string"<br>
where<br>
Error = s words<br>
Errornumber =
Error(ErrorNumber _ _ )<br>
Errorcode = Error(_ Errorcode
_ )<br>
<br>
but now I cannot use where :( <br>
<br>
Roelof<br>
<br>
<br>
<br>
<br>
Roelof Wobben schreef op 23-2-2015
om 16:10:<br>
</div>
<blockquote type="cite">
<div>Oke, <br>
<br>
Then I make there a mistake,<br>
<br>
What I try to do is to send the
file to parseMessage and let
IsValid check if it´s have the
right format. <br>
<br>
Then after the where I try to
check if the function isValid
returns true or false. <br>
<br>
Roelof<br>
<br>
<br>
Konstantine Rybnikov schreef op
23-2-2015 om 16:03:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>
<div>
<div>Roelof,<br>
<br>
</div>
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.<br>
<br>
</div>
My suggestion is to rename
second isValid.<br>
<br>
</div>
Good luck.<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon,
Feb 23, 2015 at 4:50 PM,
Roelof Wobben <span dir="ltr"><<a href="mailto:r.wobben@home.nl" target="_blank">r.wobben@home.nl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>Chaddaï Fouché
schreef op 23-2-2015 om
13:20:<br>
</div>
<span>
<blockquote type="cite">
<div dir="ltr">
<div>Note that
Roelof is doing
the CIS 194
Homework <a href="http://www.seas.upenn.edu/%7Ecis194/fall14/hw/03-ADTs.pdf" target="_blank">http://www.seas.upenn.edu/~cis194/fall14/hw/03-ADTs.pdf</a>
(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.<br>
<br>
<br>
-- <br>
</div>
Jedaï<br>
</div>
</blockquote>
<br>
</span> Correct and Im
trying to do exercise 1 of
Week 2,<br>
<br>
I have tried this solution
: <br>
<br>
-- | Main entry point to
the application.<br>
{-# OPTIONS_GHC -Wall #-}<br>
<br>
module LogAnalysis where<br>
<br>
import Log;<br>
import Data.Char
(isLetter, isDigit) <br>
<br>
isValid :: [Char] ->
Bool <br>
isValid s = go (words s)<br>
where<br>
go ([a]:b:_) =
isLetter a && all
isDigit b<br>
go _ = False
<br>
<br>
parseMessage :: [Char]
-> [Char]<br>
parseMessage s = isValid s
<br>
where <br>
isValid = "Geldige
string"<br>
_ =
"Ongeldige string"<br>
<br>
-- | The main entry point.<br>
main :: IO ()<br>
main = do<br>
putStrLn $
parseMessage "I 4764 He
trusts to you to set them
free," <br>
<br>
<br>
but I see this error
message : <br>
<br>
<div>src/LogAnalysis.hs@16:18-16:27
</div>
<div><span>Couldn't match
expected type ‘[Char]
-> [Char]’ with
actual type </span>
<div style="font-size:14px">[<span>Char</span>]</div>
<span> The function </span>
<div style="font-size:14px"><span>isValid</span></div>
<span> is applied to one
argument, but its type
</span>
<div style="font-size:14px">[<span>Char</span>]</div>
<span> has none</span><span title="Click to
show/hide extra
information"> …</span><span style="display:inline">
In the expression:
isValid s In an
equation for
‘parseMessage’:
parseMessage s =
isValid s where
isValid = "Geldige
string" _ = "Ongeldige
string"<br>
<br>
<br>
</span></div>
<br>
</div>
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