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Today's Topics:
1. IO operations (Alexander Chen)
2. Re: IO operations (Francesco Ariis)
3. Re: IO operations (Alexander Klink)
4. Re: IO operations (Tobias Brandt)
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Message: 1
Date: Thu, 13 Aug 2020 13:02:19 +0200 (CEST)
From: Alexander Chen <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] IO operations
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"
Hi,
module Main where
allwords :: IO Int
allwords = do
dict <- readFile "data/dict.txt"
return $ length [x | x <- dict , not $ '-' `elem` x]
main :: IO Int
main = do allwords
error
* Couldn't match expected type `t0 Char' with actual type `Char'
* In the second argument of `elem', namely `x'
In the second argument of `($)', namely '-' `elem` x
In the expression: not $ '-' `elem` x
could someone tell me what I am doing wrong?
thanks!
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Message: 2
Date: Thu, 13 Aug 2020 13:19:26 +0200
From: Francesco Ariis <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] IO operations
Message-ID: <20200813111926.GC2065@extensa>
Content-Type: text/plain; charset=utf-8
Hello Alexander
Il 13 agosto 2020 alle 13:02 Alexander Chen ha scritto:
> allwords :: IO Int
> allwords = do
> dict <- readFile "data/dict.txt"
> return $ length [x | x <- dict , not $ '-' `elem` x]
`elem` has type:
λ> :t elem
elem :: Eq a => a -> [a] -> Bool
-- almost
You are comparing '-' (a `Char`) with `x` (another `Char`), hence you
only need `==`. Does this make sense?
—F
------------------------------
Message: 3
Date: Thu, 13 Aug 2020 13:24:00 +0200
From: Alexander Klink <[email protected]>
To: Alexander Chen <[email protected]>, The Haskell-Beginners
Mailing List - Discussion of primarily beginner-level topics related
to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] IO operations
Message-ID: <[email protected]>
Content-Type: text/plain; charset=iso-8859-1
On Thu, Aug 13, 2020 at 01:02:19PM +0200, Alexander Chen wrote:
> module Main where
>
> allwords :: IO Int
> allwords = do
> dict <- readFile "data/dict.txt"
> return $ length [x | x <- dict , not $ '-' `elem` x]
>
> main :: IO Int
> main = do allwords
>
> error
>
> * Couldn't match expected type `t0 Char' with actual type `Char'
> * In the second argument of `elem', namely `x'
> In the second argument of `($)', namely '-' `elem` x
> In the expression: not $ '-' `elem` x
>
> could someone tell me what I am doing wrong?
dict is of type String, since it's a String containing the complete
file. That's why the type complaint is that you want to check if '-' (a
Char) is an element of x, which is also a Char, which cannot work.
I asssume what you want is a list of lines, which you can by
applying the lines function, e.g. here:
return $ length [x | x <- lines dict , not $ '-' `elem` x]
HTH,
Cheers,
Alex
------------------------------
Message: 4
Date: Thu, 13 Aug 2020 13:14:39 +0200
From: Tobias Brandt <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] IO operations
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"; Format="flowed"
Hey Alexander,
|dict| has type |String|. Therefore, |x| is of type |Char|, but |elem
'-'| is of type |[Char] -> Bool| (simplified). Hence, you get a type
mismatch. If you just want to count every character except |'-'|, then
you could just you |'-' /= x|.
Cheers
Tobias
On 8/13/20 1:02 PM, Alexander Chen wrote:
> Hi,
>
> module Main where
> allwords :: IO Int
> allwords = do
> dict <- readFile "data/dict.txt"
> return $ length [x | x <- dict , not $ '-' `elem` x]
> main :: IO Int
> main = do allwords
>
> error
>
> * Couldn't match expected type `t0 Char' with actual type `Char'
> * In the second argument of `elem', namely `x'
> In the second argument of `($)', namely '-' `elem` x
> In the expression: not $ '-' `elem` x
>
>
> could someone tell me what I am doing wrong?
>
> thanks!
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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