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<div class="moz-cite-prefix">Thanks, <br>
<br>
Can I somehow also test if the string is valid so that the
isvalid function is used. <br>
<br>
Roelof<br>
<br>
Alex Hammel schreef op 23-2-2015 om 21:23:<br>
</div>
<blockquote
cite="mid:CA+_xFeofMmx-vZ0RuY7w0XJFu_STxzAnDeCendrh0HVaPMCs5A@mail.gmail.com"
type="cite">
<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 moz-do-not-send="true"
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
moz-do-not-send="true"
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
moz-do-not-send="true"
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
moz-do-not-send="true"
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
moz-do-not-send="true" 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
moz-do-not-send="true"
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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