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Today's Topics:
1. Confusing Show/print error (Galaxy Being)
2. Re: Confusing Show/print error (Francesco Ariis)
3. Re: Confusing Show/print error (Tobias Brandt)
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Message: 1
Date: Thu, 9 Sep 2021 16:25:58 -0500
From: Galaxy Being <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Confusing Show/print error
Message-ID:
<cafahfsvxqqo9surro9vqkq7_40get2q8wbyb8tssbdnaomy...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I've got this
import Data.Tuple
fswp :: (a, b) -> (b, a)
fswp = Data.Tuple.swap
and get this
• No instance for (Show ((a0, b0) -> (b0, a0)))
arising from a use of ‘print’
(maybe you haven't applied a function to enough arguments?)
• In a stmt of an interactive GHCi command: print it
Not sure why or what to do to correct it.
⨽
Lawrence Bottorff
Grand Marais, MN, USA
[email protected]
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Message: 2
Date: Thu, 9 Sep 2021 23:51:38 +0200
From: Francesco Ariis <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] Confusing Show/print error
Message-ID: <YTqB6jg6vTcm8ofw@extensa>
Content-Type: text/plain; charset=utf-8
Hello Lawrence,
Il 09 settembre 2021 alle 16:25 Galaxy Being ha scritto:
> import Data.Tuple
> fswp :: (a, b) -> (b, a)
> fswp = Data.Tuple.swap
this typechecks without problem.
maybe you invoked fswp without an argument? (i.e. `λ> fwsp`
instead of `λ> fwsp (1,'a')`)
------------------------------
Message: 3
Date: Thu, 9 Sep 2021 23:56:58 +0200
From: Tobias Brandt <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] Confusing Show/print error
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"; Format="flowed"
Hi Lawrence,
it seems that you are trying to print your defined function. Most likely
you just forgot to apply an argument to fswp. So 'fswp (1,2)' should
just work fine.
Cheers,
Tobias
On 9/9/21 11:25 PM, Galaxy Being wrote:
> I've got this
>
> import Data.Tuple
> fswp :: (a, b) -> (b, a)
> fswp = Data.Tuple.swap
>
> and get this
>
> • No instance for (Show ((a0, b0) -> (b0, a0)))
> arising from a use of ‘print’
> (maybe you haven't applied a function to enough arguments?)
> • In a stmt of an interactive GHCi command: print it
>
> Not sure why or what to do to correct it.
>
> ⨽
> Lawrence Bottorff
> Grand Marais, MN, USA
> [email protected] <mailto:[email protected]>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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