[Haskell-beginners] the flag -N2 requires the program to be built with -threaded

[Jung Kim]

I changed to the suggested solution and that fixes the problem. Thank
you very much!

On 23 March 2016 at 14:25, Sumit Sahrawat, Maths & Computing, IIT
(BHU) <sumit.sahrawat.apm13 at iitbhu.ac.in> wrote:
> As there are a lot of options, ghc has a `--show-options` flag which shows
> them all. The `-threaded` flag is to be passed to ghc.
> I think the second command in the `all` block is redundant, as `ghc -O
> mvar.hs` should produce a binary named mvar.
>
> This should work:
>
> all:
>     ghc -O -threaded mvar.hs
>
> Regards,
>   Sumit
>
> On 23 March 2016 at 10:49, Jung Kim <jungkkr at gmail.com> wrote:
>>
>> I am currently reading an article[1] where the author uses Haskell to
>> explain her idea. The problem is I don't understand Haskell and am not
>> familiar with Haskell concept like MVar, IVar, etc. (I can get the
>> code compile, and have several years programming experiences.)
>>
>> When testing the code, it throws the error messages "the flag -N2
>> requires the program to be built with -threaded"; however I can't find
>> thread related flag with ghc command by `ghc --help`. How can I fix
>> this problem?
>>
>> Environment I use: Debian stretch/sid, kernel 4.0.0-2-rt-686-pae, GHC
>> version 7.10.3.
>>
>> The code is exactly the same as described in the section
>> 'Nondeterminism with MVars' of article; and the makefile content is
>>
>> all:
>>         ghc -O mvar.hs
>>         ghc -o mvar mvar.o
>> run:
>>         ./execute # while true; do ./mvar +RTS -N2; done
>> clean:
>>         rm mvar
>>
>> Thanks
>>
>> [1].
>> http://composition.al/blog/2013/09/22/some-example-mvar-ivar-and-lvar-programs-in-haskell/
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>
>
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