Send Beginners mailing list submissions to
[email protected]
To subscribe or unsubscribe via the World Wide Web, visit
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
or, via email, send a message with subject or body 'help' to
[email protected]
You can reach the person managing the list at
[email protected]
When replying, please edit your Subject line so it is more specific
than "Re: Contents of Beginners digest..."
Today's Topics:
1. database error simply by using a sting in a variable
(Damien Mattei)
2. Re: database error simply by using a sting in a variable
(Francesco Ariis)
3. Re: (SPAM 3)Re: database error simply by using a sting in a
variable (Damien Mattei)
4. Re: (SPAM 3)Re: database error simply by using a sting in a
variable (Damien Mattei)
5. Re: (SPAM 3)Re: database error simply by using a sting in a
variable (Francesco Ariis)
6. Re: database error simply by using a sting in a variable
(Ian Denhardt)
7. Regex (mike h)
8. database, list result, extraction and conversion (Damien Mattei)
----------------------------------------------------------------------
Message: 1
Date: Wed, 5 Dec 2018 17:02:48 +0100
From: Damien Mattei <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] database error simply by using a sting in
a variable
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
why i'm getting this error?
code:
let name = "'A 20'"
let qry = "select `N° BD` from Coordonnées where Nom = " ++ name
putStrLn qry
bd_rows <- query_ conn qry
putStrLn $ show bd_rows
putStrLn $ show name
forM_ bd_rows $ \(Only a) ->
putStrLn $ Text.unpack a
error:
*Main> :load UpdateSidonie
[1 of 1] Compiling Main ( UpdateSidonie.hs, interpreted )
UpdateSidonie.hs:74:28: error:
• Couldn't match expected type ‘Query’ with actual type ‘[Char]’
• In the second argument of ‘query_’, namely ‘qry’
In a stmt of a 'do' block: bd_rows <- query_ conn qry
In the expression:
do conn <- connect
defaultConnectInfo
{connectHost = "moita", connectUser = "mattei",
connectPassword = "sidonie2", connectDatabase =
"sidonie"}
rows <- query_
conn
"SELECT Nom,distance FROM AngularDistance WHERE
distance > 0.000278"
forM_ rows
$ \ (name, distance)
-> putStrLn $ unpack name ++ " " ++ show (distance ::
Double)
let name = "'A 20'"
....
|
74 | bd_rows <- query_ conn qry
| ^^^
Failed, no modules loaded.
--
[email protected], [email protected], UNS / OCA / CNRS
------------------------------
Message: 2
Date: Wed, 5 Dec 2018 17:12:03 +0100
From: Francesco Ariis <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] database error simply by using a
sting in a variable
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Hello Damien,
On Wed, Dec 05, 2018 at 05:02:48PM +0100, Damien Mattei wrote:
> • Couldn't match expected type ‘Query’ with actual type ‘[Char]’
GHC would like to have a `Query`, but you are providing a `String`.
You didn't specify which library you are using, but I am willing to
bet there is an appropriate ":: String -> Query" function.
That of you need to put
{-# Language OverloadedStrings -#}
on top of your file. Does that work?
-F
------------------------------
Message: 3
Date: Wed, 5 Dec 2018 17:28:03 +0100
From: Damien Mattei <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] (SPAM 3)Re: database error simply by
using a sting in a variable
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Le 05/12/2018 17:12, Francesco Ariis a écrit :
> Hello Damien,
>
> On Wed, Dec 05, 2018 at 05:02:48PM +0100, Damien Mattei wrote:
>> • Couldn't match expected type ‘Query’ with actual type ‘[Char]’
>
> GHC would like to have a `Query`, but you are providing a `String`.
> You didn't specify which library you are using, but I am willing to
> bet there is an appropriate ":: String -> Query" function.
>
> That of you need to put
>
> {-# Language OverloadedStrings -#}
i had put it alreeady
>
> on top of your file. Does that work?
no
i begin to understand that {-# Language OverloadedStrings -#} is working
on string but not on string in variable or concatenation , i should have
to create an object of type Query from the String... ???
finally ,having a beginning of solution:
let qry_head = "select `N° BD` from sidonie.Coordonnées where Nom = ?"
:: Query
putStrLn qry
bd_rows <- query conn qry_head (Only (name::String))
> -F
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
--
[email protected], [email protected], UNS / OCA / CNRS
------------------------------
Message: 4
Date: Wed, 5 Dec 2018 17:28:43 +0100
From: Damien Mattei <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] (SPAM 3)Re: database error simply by
using a sting in a variable
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
thanks for your help
Le 05/12/2018 17:12, Francesco Ariis a écrit :
> Hello Damien,
>
> On Wed, Dec 05, 2018 at 05:02:48PM +0100, Damien Mattei wrote:
>> • Couldn't match expected type ‘Query’ with actual type ‘[Char]’
>
> GHC would like to have a `Query`, but you are providing a `String`.
> You didn't specify which library you are using, but I am willing to
> bet there is an appropriate ":: String -> Query" function.
>
> That of you need to put
>
> {-# Language OverloadedStrings -#}
>
> on top of your file. Does that work?
> -F
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
--
[email protected], [email protected], UNS / OCA / CNRS
------------------------------
Message: 5
Date: Wed, 5 Dec 2018 17:46:55 +0100
From: Francesco Ariis <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] (SPAM 3)Re: database error simply by
using a sting in a variable
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
On Wed, Dec 05, 2018 at 05:28:03PM +0100, Damien Mattei wrote:
> i begin to understand that {-# Language OverloadedStrings -#} is working
> on string but not on string in variable or concatenation , i should have
> to create an object of type Query from the String... ???
Yes, OverloadedStrings works on String *literals* not on String variables!
------------------------------
Message: 6
Date: Wed, 05 Dec 2018 13:19:26 -0500
From: Ian Denhardt <[email protected]>
To: Damien Mattei <[email protected]>, The Haskell-Beginners Mailing List
- Discussion of primarily beginner-level topics related to Haskell
<[email protected]>
Subject: Re: [Haskell-beginners] database error simply by using a
sting in a variable
Message-ID: <154403396683.872.1499410688028997872@localhost>
Content-Type: text/plain; charset="utf-8"
It sounds from the later posts like you've made some progress. I just
want to call out one thing:
Quoting Damien Mattei (2018-12-05 11:02:48)
> let name = "'A 20'"
> let qry = "select `N° BD` from Coordonnées where Nom = " ++ name
I'll hazard a guess that you're using the sqlite-simple library. From
their documentation on the Query type:
> This type is intended to make it difficult to construct a SQL query by
> concatenating string fragments, as that is an extremely common way to
> accidentally introduce SQL injection vulnerabilities into an
> application.
From later messages it looks like you worked out the OverloadedStrings
thing and ended up (correctly) moving to some code that uses the ?
interpolation syntax: ".... where Nom = ?". I just wanted to stress that
this is the right way to do things, and the distinction is important.
This is a general thing when working with SQL: don't construct queries
by gluing strings together; it's a great way to have vulnerabilities in
your app.
Happy Hacking,
-Ian
------------------------------
Message: 7
Date: Thu, 6 Dec 2018 10:38:06 +0000
From: mike h <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Regex
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
Hi,
Which package is the most popular and/or easy to used for dealing with regular
expressions?
My regex is quite simple and I just need to get 2 or 3 capture groups from the
result.
Many thanks
Mike
------------------------------
Message: 8
Date: Thu, 6 Dec 2018 12:16:08 +0100
From: Damien Mattei <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] database, list result, extraction and
conversion
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
again un haskell beginner question ;-) ...
i have this: [Only {fromOnly = "-04.3982"}]
as result of a database query, i understand it's a list and i can get
the first element:
*Main> Data.List.head [Only {fromOnly = "-04.3982"}]
Only {fromOnly = "-04.3982"}
*Main> let s = Data.List.head [Only {fromOnly = "-04.3982"}]
*Main> s
Only {fromOnly = "-04.3982"}
*Main> show s
"Only {fromOnly = \"-04.3982\"}"
but how can i get the String "-04.3982" ? and after converting it to a Float
--
[email protected], [email protected], UNS / OCA / CNRS
------------------------------
Subject: Digest Footer
_______________________________________________
Beginners mailing list
[email protected]
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
End of Beginners Digest, Vol 126, Issue 4
*****************************************
