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Today's Topics:
1. Multiline code in GHCi (Shishir Srivastava)
2. Re: Multiline code in GHCi (divyanshu ranjan)
3. Re: Multiline code in GHCi (Brandon Allbery)
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Message: 1
Date: Fri, 7 Aug 2015 16:15:11 +0100
From: Shishir Srivastava <[email protected]>
To: beginners <[email protected]>
Subject: [Haskell-beginners] Multiline code in GHCi
Message-ID:
<CALe5RTs5_2uekv4MZuGNREPzE_Z+aUzDoMHz=12nvabxlqs...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
I am trying to run this basic multiline code in GHCi. I am not sure if this
is even possible without writing it in a file and compiling it in a
traditional way.
-------
Prelude> :set +m
Prelude> let main1 = do
Prelude| a <- readLn
Prelude| return a
Prelude|
Prelude>
Prelude> main1
<interactive>:75:1:
No instance for (Show (IO b0)) arising from a use of `print'
In the first argument of `print', namely `it'
In a stmt of an interactive GHCi command: print it
-------
Could someone please confirm if the function can be defined and called like
this in GHCi or point to where am going wrong.
Thanks,
Shishir Srivastava
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Message: 2
Date: Fri, 7 Aug 2015 21:19:39 +0530
From: divyanshu ranjan <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Multiline code in GHCi
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Hi Shishir,
If you wrap multiline code in between
Prelude> :{
Prelude| let main1 = do
Prelude| a <- getLine
Prelude| return a
Prelude| :}
Prelude> main1
hello
"hello"
It will work.
On Fri, Aug 7, 2015 at 8:45 PM, Shishir Srivastava <
[email protected]> wrote:
> Hi,
>
> I am trying to run this basic multiline code in GHCi. I am not sure if
> this is even possible without writing it in a file and compiling it in a
> traditional way.
>
> -------
> Prelude> :set +m
> Prelude> let main1 = do
> Prelude| a <- readLn
> Prelude| return a
> Prelude|
> Prelude>
> Prelude> main1
>
> <interactive>:75:1:
> No instance for (Show (IO b0)) arising from a use of `print'
> In the first argument of `print', namely `it'
> In a stmt of an interactive GHCi command: print it
> -------
>
> Could someone please confirm if the function can be defined and called
> like this in GHCi or point to where am going wrong.
>
> Thanks,
> Shishir Srivastava
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
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Message: 3
Date: Fri, 7 Aug 2015 11:51:00 -0400
From: Brandon Allbery <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Multiline code in GHCi
Message-ID:
<CAKFCL4WOPw++3s_23O9259rV7Q1KAFeqd-K+K54Xa32=a7v...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
On Fri, Aug 7, 2015 at 11:15 AM, Shishir Srivastava <
[email protected]> wrote:
> Prelude> :set +m
> Prelude> let main1 = do
> Prelude| a <- readLn
> Prelude| return a
> Prelude|
> Prelude>
> Prelude> main1
>
> <interactive>:75:1:
> No instance for (Show (IO b0)) arising from a use of `print'
>
In an actual program, it would be able to apply defaulting rules and
monomorphize `b0` to Integer. The somewhat unusual ghci environment, in
particular how it tries to figure out whether to evaluate an expression and
`print` the result or instead run an IO action --- coupled with the
monomorphism restriction being disabled in the interactive context in ghci
7.8 and later --- is working against you here. As a result, you need to
specify a result type when invoking `main1`, which is what the error
message is telling you.
--
brandon s allbery kf8nh sine nomine associates
[email protected] [email protected]
unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net
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