From hjgtuyl at chello.nl  Fri Mar  1 18:02:42 2019
From: hjgtuyl at chello.nl (Henk-Jan van Tuyl)
Date: Fri, 01 Mar 2019 19:02:42 +0100
Subject: [Haskell-beginners] Error Message: Can not find C library. How
 can I do this?
In-Reply-To: <CAJp-Nqw2Gboja9wVqRebA_pOMdak6bGQA7jKm3=KshYxoDfpmA@mail.gmail.com>
References: <CAJp-Nqw2Gboja9wVqRebA_pOMdak6bGQA7jKm3=KshYxoDfpmA@mail.gmail.com>
Message-ID: <op.zxzi2whfpz0j5l@alquantor>


Did you try setting environment variable LIBRARY_PATH?
Something like:
     Set LIBRARY_PATH=%LIBRARY_PATH%;C:\wxWidgets\lib
You might need to set C_INCLUDE_PATH as well, for the header files.

Regards,
Henk-Jan van Tuyl



On Tue, 26 Feb 2019 07:47:59 +0100, S. H. Aegis <shaegis at gmail.com> wrote:

> Hello.
>
> I’m new to stack & FFI.
>
> I created a dll file by http://www.mingw.org/wiki/sampleDLL
>
[...]
> *Configuring test2-0.1.0.0...*
> *Cabal-simple_Z6RU0evB_2.4.0.1_ghc-8.6.3.exe: Missing dependency on a
> foreign*
> *library:*
> ** Missing (or bad) C library: example_dll.a*
[...]
> How can I fix this? I did a lot of things on the webpages, but I could  
> not.
>
> Please, help me.
>
>
>
> Sincerely, S. Chang.


-- 
Message from Stanford University:

Folding at home

What if you could share your unused computer power to help find a cure? In
just 5 minutes you can join the world's biggest networked computer and get
us closer sooner. Watch the video.
http://foldingathome.stanford.edu/

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http://members.chello.nl/hjgtuyl/tourdemonad.html
Haskell programming
--

From edgar.klerks at gmail.com  Fri Mar  1 19:42:01 2019
From: edgar.klerks at gmail.com (Edgar Klerks)
Date: Fri, 1 Mar 2019 20:42:01 +0100
Subject: [Haskell-beginners] Error Message: Can not find C library. How
 can I do this?
In-Reply-To: <CAJp-Nqw2Gboja9wVqRebA_pOMdak6bGQA7jKm3=KshYxoDfpmA@mail.gmail.com>
References: <CAJp-Nqw2Gboja9wVqRebA_pOMdak6bGQA7jKm3=KshYxoDfpmA@mail.gmail.com>
Message-ID: <CAGAUyt=xUg7Y0k1ZnbMqQwehcXzBbbQj102QA+m5HWq5ZZrmgw@mail.gmail.com>

You made a small typo:

example_dll.cpp, example_dll.dll, example_dll.h, example_dll.o,
example_exe.cpp, *libexample_dll.a*

And in your code, you call it example_dll.a instead of libexample_dll.a:

>
>   extra-libraries:
>     - example_dll.a
>

That should probably be:

  extra-libraries:
    - libexample_dll.a


On Tue, Feb 26, 2019 at 7:48 AM S. H. Aegis <shaegis at gmail.com> wrote:

> Hello.
>
> I’m new to stack & FFI.
>
> I created a dll file by http://www.mingw.org/wiki/sampleDLL
>
> And I put all files into dll folder. (Those files are example_dll.cpp,
> example_dll.dll, example_dll.h, example_dll.o, example_exe.cpp,
> libexample_dll.a) I test example_exe.exe file, and confirmed that works.
>
> (Windows7 Pro, stack 1.9.3)
>
> <package.yaml>
>
> executables:
>
>   test2-exe:
>
>     main:                Main.hs
>
>     source-dirs:         app
>
>     ghc-options:
>
>     - -threaded
>
>     - -rtsopts
>
>     - -with-rtsopts=-N
>
>     dependencies:
>
>     - test2
>
>     extra-libraries:
>
>     - example_dll.a
>
>     extra-lib-dirs:
>
>     - dll
>
> <stack.yaml>
>
> # Extra directories used by stack for building
>
> extra-include-dirs:
>
>   - dll
>
> extra-lib-dirs:
>
>   - dll
>
> <Main.hs>
>
> {-# LANGUAGE ForeignFunctionInterface #-}
>
>
>
> module Main where
>
>
>
> -- import Lib
>
> import Foreign
>
>
>
> foreign import ccall "example_dll.h hello"
>
>     c_hello :: IO()
>
>
>
> main :: IO ()
>
> main = c_hello
>
> <example_dll.cpp>
>
> #include <stdio.h>
>
> #include "example_dll.h"
>
>
>
> __stdcall void hello(const char *s)
>
> {
>
>         printf("Hello %s\n", s);
>
> }
>
> int Double(int x)
>
> {
>
>         return 2 * x;
>
> }
>
> void CppFunc(void)
>
> {
>
>         puts("CppFunc");
>
> }
>
> void MyClass::func(void)
>
> {
>
>         puts("MyClass.func()");
>
> }
>
>
>
> When I try to stack build, I get error messages.
>
>
>
> *C:\Users\shaegis\Documents\Haskell\test2\dll>stack build*
>
> *Building all executables for `test2' once. After a successful build of
> all of them, only specified executables will be rebuilt.*
>
> *test2-0.1.0.0: configure (lib + exe)*
>
> *Configuring test2-0.1.0.0...*
>
> *Cabal-simple_Z6RU0evB_2.4.0.1_ghc-8.6.3.exe: Missing dependency on a
> foreign*
>
> *library:*
>
> ** Missing (or bad) C library: example_dll.a*
>
> *This problem can usually be solved by installing the system package that*
>
> *provides this library (you may need the "-dev" version). If the library
> is*
>
> *already installed but in a non-standard location then you can use the
> flags*
>
> *--extra-include-dirs= and --extra-lib-dirs= to specify where it is.If the*
>
> *library file does exist, it may contain errors that are caught by the C*
>
> *compiler at the preprocessing stage. In this case you can re-run
> configure*
>
> *with the verbosity flag -v3 to see the error messages.*
>
>
>
> *--  While building package test2-0.1.0.0 using:*
>
> *
> C:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_Z6RU0evB_2.4.0.1_ghc-8.6.3.exe
> --builddir=.stack-work\dist\e626a42b configure
> --with-ghc=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\ghc-8.6.3\bin\ghc.EXE
> --with-ghc-pkg=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\ghc-8.6.3\bin\ghc-pkg.EXE
> --user --package-db=clear --package-db=global
> --package-db=C:\sr\snapshots\3233b5e2\pkgdb
> --package-db=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\pkgdb
> --libdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\lib
> --bindir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\bin
> --datadir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\share
> --libexecdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\libexec
> --sysconfdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\etc
> --docdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\doc\test2-0.1.0.0
> --htmldir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\doc\test2-0.1.0.0
> --haddockdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\doc\test2-0.1.0.0
> --dependency=base=base-4.12.0.0
> --extra-include-dirs=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\msys2-20180531\mingw64\include
> --extra-include-dirs=C:\Users\shaegis\Documents\Haskell\test2\dll
> --extra-lib-dirs=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\msys2-20180531\mingw64\bin
> --extra-lib-dirs=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\msys2-20180531\mingw64\lib
> --extra-lib-dirs=C:\Users\shaegis\Documents\Haskell\test2\dll
> --enable-tests --enable-benchmarks*
>
> *Process exited with code: ExitFailure 1*
>
>
>
> How can I fix this? I did a lot of things on the webpages, but I could not.
>
> Please, help me.
>
>
>
> Sincerely, S. Chang.
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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From shaegis at gmail.com  Sat Mar  2 02:35:47 2019
From: shaegis at gmail.com (S. H. Aegis)
Date: Sat, 2 Mar 2019 11:35:47 +0900
Subject: [Haskell-beginners] Error Message: Can not find C library. How
 can I do this?
In-Reply-To: <op.zxzi2whfpz0j5l@alquantor>
References: <CAJp-Nqw2Gboja9wVqRebA_pOMdak6bGQA7jKm3=KshYxoDfpmA@mail.gmail.com>
 <op.zxzi2whfpz0j5l@alquantor>
Message-ID: <CAJp-NqzNW_dKBkuXZinesa8t=VZNLDcD1yp1DH289mBUvv7_ew@mail.gmail.com>

Thank you to your kind reply. =)
I tried several times, but still got a same error message. (ㅠㅠ)
But I'm going to googling with key-word that you told me.
Thank you again.

Best reguard
S. Chang.

2019년 3월 2일 (토) 오전 3:03, Henk-Jan van Tuyl <hjgtuyl at chello.nl>님이 작성:

>
> Did you try setting environment variable LIBRARY_PATH?
> Something like:
>      Set LIBRARY_PATH=%LIBRARY_PATH%;C:\wxWidgets\lib
> You might need to set C_INCLUDE_PATH as well, for the header files.
>
> Regards,
> Henk-Jan van Tuyl
>
>
>
> On Tue, 26 Feb 2019 07:47:59 +0100, S. H. Aegis <shaegis at gmail.com> wrote:
>
> > Hello.
> >
> > I’m new to stack & FFI.
> >
> > I created a dll file by http://www.mingw.org/wiki/sampleDLL
> >
> [...]
> > *Configuring test2-0.1.0.0...*
> > *Cabal-simple_Z6RU0evB_2.4.0.1_ghc-8.6.3.exe: Missing dependency on a
> > foreign*
> > *library:*
> > ** Missing (or bad) C library: example_dll.a*
> [...]
> > How can I fix this? I did a lot of things on the webpages, but I could
> > not.
> >
> > Please, help me.
> >
> >
> >
> > Sincerely, S. Chang.
>
>
> --
> Message from Stanford University:
>
> Folding at home
>
> What if you could share your unused computer power to help find a cure? In
> just 5 minutes you can join the world's biggest networked computer and get
> us closer sooner. Watch the video.
> http://foldingathome.stanford.edu/
>
> --
> http://members.chello.nl/hjgtuyl/tourdemonad.html
> Haskell programming
> --
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>


-- 
Sok Ha, CHANG
Dr. Chang's Clinic. #203. 503-23. AmSa-Dong, GangDong-Gu, Seoul.
Tel: +82-2-442-7585
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From shaegis at gmail.com  Sat Mar  2 02:37:12 2019
From: shaegis at gmail.com (S. H. Aegis)
Date: Sat, 2 Mar 2019 11:37:12 +0900
Subject: [Haskell-beginners] Error Message: Can not find C library. How
 can I do this?
In-Reply-To: <CAGAUyt=xUg7Y0k1ZnbMqQwehcXzBbbQj102QA+m5HWq5ZZrmgw@mail.gmail.com>
References: <CAJp-Nqw2Gboja9wVqRebA_pOMdak6bGQA7jKm3=KshYxoDfpmA@mail.gmail.com>
 <CAGAUyt=xUg7Y0k1ZnbMqQwehcXzBbbQj102QA+m5HWq5ZZrmgw@mail.gmail.com>
Message-ID: <CAJp-Nqy8Q-b8tjQwxA3z8yvovFvROn4xsyp2gEjBcLudHk6RCw@mail.gmail.com>

 Thank you to your kind reply. =)
Unfortunately, I've got same error message.
Thank you again.

Best reguard
S. Chang.

2019년 3월 2일 (토) 오전 4:42, Edgar Klerks <edgar.klerks at gmail.com>님이 작성:

> You made a small typo:
>
> example_dll.cpp, example_dll.dll, example_dll.h, example_dll.o,
> example_exe.cpp, *libexample_dll.a*
>
> And in your code, you call it example_dll.a instead of libexample_dll.a:
>
>>
>>   extra-libraries:
>>     - example_dll.a
>>
>
> That should probably be:
>
>   extra-libraries:
>     - libexample_dll.a
>
>
> On Tue, Feb 26, 2019 at 7:48 AM S. H. Aegis <shaegis at gmail.com> wrote:
>
>> Hello.
>>
>> I’m new to stack & FFI.
>>
>> I created a dll file by http://www.mingw.org/wiki/sampleDLL
>>
>> And I put all files into dll folder. (Those files are example_dll.cpp,
>> example_dll.dll, example_dll.h, example_dll.o, example_exe.cpp,
>> libexample_dll.a) I test example_exe.exe file, and confirmed that works.
>>
>> (Windows7 Pro, stack 1.9.3)
>>
>> <package.yaml>
>>
>> executables:
>>
>>   test2-exe:
>>
>>     main:                Main.hs
>>
>>     source-dirs:         app
>>
>>     ghc-options:
>>
>>     - -threaded
>>
>>     - -rtsopts
>>
>>     - -with-rtsopts=-N
>>
>>     dependencies:
>>
>>     - test2
>>
>>     extra-libraries:
>>
>>     - example_dll.a
>>
>>     extra-lib-dirs:
>>
>>     - dll
>>
>> <stack.yaml>
>>
>> # Extra directories used by stack for building
>>
>> extra-include-dirs:
>>
>>   - dll
>>
>> extra-lib-dirs:
>>
>>   - dll
>>
>> <Main.hs>
>>
>> {-# LANGUAGE ForeignFunctionInterface #-}
>>
>>
>>
>> module Main where
>>
>>
>>
>> -- import Lib
>>
>> import Foreign
>>
>>
>>
>> foreign import ccall "example_dll.h hello"
>>
>>     c_hello :: IO()
>>
>>
>>
>> main :: IO ()
>>
>> main = c_hello
>>
>> <example_dll.cpp>
>>
>> #include <stdio.h>
>>
>> #include "example_dll.h"
>>
>>
>>
>> __stdcall void hello(const char *s)
>>
>> {
>>
>>         printf("Hello %s\n", s);
>>
>> }
>>
>> int Double(int x)
>>
>> {
>>
>>         return 2 * x;
>>
>> }
>>
>> void CppFunc(void)
>>
>> {
>>
>>         puts("CppFunc");
>>
>> }
>>
>> void MyClass::func(void)
>>
>> {
>>
>>         puts("MyClass.func()");
>>
>> }
>>
>>
>>
>> When I try to stack build, I get error messages.
>>
>>
>>
>> *C:\Users\shaegis\Documents\Haskell\test2\dll>stack build*
>>
>> *Building all executables for `test2' once. After a successful build of
>> all of them, only specified executables will be rebuilt.*
>>
>> *test2-0.1.0.0: configure (lib + exe)*
>>
>> *Configuring test2-0.1.0.0...*
>>
>> *Cabal-simple_Z6RU0evB_2.4.0.1_ghc-8.6.3.exe: Missing dependency on a
>> foreign*
>>
>> *library:*
>>
>> ** Missing (or bad) C library: example_dll.a*
>>
>> *This problem can usually be solved by installing the system package that*
>>
>> *provides this library (you may need the "-dev" version). If the library
>> is*
>>
>> *already installed but in a non-standard location then you can use the
>> flags*
>>
>> *--extra-include-dirs= and --extra-lib-dirs= to specify where it is.If
>> the*
>>
>> *library file does exist, it may contain errors that are caught by the C*
>>
>> *compiler at the preprocessing stage. In this case you can re-run
>> configure*
>>
>> *with the verbosity flag -v3 to see the error messages.*
>>
>>
>>
>> *--  While building package test2-0.1.0.0 using:*
>>
>> *
>> C:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_Z6RU0evB_2.4.0.1_ghc-8.6.3.exe
>> --builddir=.stack-work\dist\e626a42b configure
>> --with-ghc=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\ghc-8.6.3\bin\ghc.EXE
>> --with-ghc-pkg=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\ghc-8.6.3\bin\ghc-pkg.EXE
>> --user --package-db=clear --package-db=global
>> --package-db=C:\sr\snapshots\3233b5e2\pkgdb
>> --package-db=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\pkgdb
>> --libdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\lib
>> --bindir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\bin
>> --datadir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\share
>> --libexecdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\libexec
>> --sysconfdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\etc
>> --docdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\doc\test2-0.1.0.0
>> --htmldir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\doc\test2-0.1.0.0
>> --haddockdir=C:\Users\shaegis\Documents\Haskell\test2\.stack-work\install\784ab3f0\doc\test2-0.1.0.0
>> --dependency=base=base-4.12.0.0
>> --extra-include-dirs=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\msys2-20180531\mingw64\include
>> --extra-include-dirs=C:\Users\shaegis\Documents\Haskell\test2\dll
>> --extra-lib-dirs=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\msys2-20180531\mingw64\bin
>> --extra-lib-dirs=C:\Users\shaegis\AppData\Local\Programs\stack\x86_64-windows\msys2-20180531\mingw64\lib
>> --extra-lib-dirs=C:\Users\shaegis\Documents\Haskell\test2\dll
>> --enable-tests --enable-benchmarks*
>>
>> *Process exited with code: ExitFailure 1*
>>
>>
>>
>> How can I fix this? I did a lot of things on the webpages, but I could
>> not.
>>
>> Please, help me.
>>
>>
>>
>> Sincerely, S. Chang.
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>


-- 
Sok Ha, CHANG
Dr. Chang's Clinic. #203. 503-23. AmSa-Dong, GangDong-Gu, Seoul.
Tel: +82-2-442-7585
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From mike_k_houghton at yahoo.co.uk  Thu Mar 14 11:10:06 2019
From: mike_k_houghton at yahoo.co.uk (mike h)
Date: Thu, 14 Mar 2019 11:10:06 +0000
Subject: [Haskell-beginners] Matrix and types
Message-ID: <F25F3321-F7AC-4B57-97F3-E4B340E10DC4@yahoo.co.uk>

Hi,

As an exercise I want to write a Matrix library.

Multiplication of two matrices is only defined when the the number of columns in the first matrix 
equals the number of rows in the second matrix. i.e. c1 == r2

So when writing the multiplication function I can check that  c1 == r2 and do something.
However what I really want to do, if possible, is to have the compiler catch the error. 

I’d appreciate any advice on how to approach this. I don’t want a full description of exactly what to do as that way I won’t have struggled  or argued with the compiler - which for me is the best way to learn Haskell :)


Thanks

Mike

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From fa-ml at ariis.it  Thu Mar 14 11:37:20 2019
From: fa-ml at ariis.it (Francesco Ariis)
Date: Thu, 14 Mar 2019 12:37:20 +0100
Subject: [Haskell-beginners] Matrix and types
In-Reply-To: <F25F3321-F7AC-4B57-97F3-E4B340E10DC4@yahoo.co.uk>
References: <F25F3321-F7AC-4B57-97F3-E4B340E10DC4@yahoo.co.uk>
Message-ID: <20190314113720.xim35mdypfxxqpol@x60s.casa>

Hello Mike,

On Thu, Mar 14, 2019 at 11:10:06AM +0000, mike h wrote:
> Multiplication of two matrices is only defined when the the number of columns in the first matrix 
> equals the number of rows in the second matrix. i.e. c1 == r2
> 
> So when writing the multiplication function I can check that  c1 == r2 and do something.
> However what I really want to do, if possible, is to have the compiler catch the error. 

Type-level literals [1] or any kind of similar trickery should help you
with having matrices checked at compile-time.

[1] https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html

From frederic.cogny at gmail.com  Thu Mar 14 13:12:46 2019
From: frederic.cogny at gmail.com (Frederic Cogny)
Date: Thu, 14 Mar 2019 14:12:46 +0100
Subject: [Haskell-beginners] Matrix and types
In-Reply-To: <20190314113720.xim35mdypfxxqpol@x60s.casa>
References: <F25F3321-F7AC-4B57-97F3-E4B340E10DC4@yahoo.co.uk>
 <20190314113720.xim35mdypfxxqpol@x60s.casa>
Message-ID: <CAGSugssd0pPEERe7+3gy_MeHhvpRt=Vdp_v1oXqWYXeKQ87jNg@mail.gmail.com>

The (experimental) Static module of hmatrix seems (I've used the packaged
but not that module) to do exactly that:
http://hackage.haskell.org/package/hmatrix-0.19.0.0/docs/Numeric-LinearAlgebra-Static.html



On Thu, Mar 14, 2019, 12:37 PM Francesco Ariis <fa-ml at ariis.it> wrote:

> Hello Mike,
>
> On Thu, Mar 14, 2019 at 11:10:06AM +0000, mike h wrote:
> > Multiplication of two matrices is only defined when the the number of
> columns in the first matrix
> > equals the number of rows in the second matrix. i.e. c1 == r2
> >
> > So when writing the multiplication function I can check that  c1 == r2
> and do something.
> > However what I really want to do, if possible, is to have the compiler
> catch the error.
>
> Type-level literals [1] or any kind of similar trickery should help you
> with having matrices checked at compile-time.
>
> [1]
> https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
-- 
Frederic Cogny
+33 7 83 12 61 69
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From mike_k_houghton at yahoo.co.uk  Thu Mar 14 15:19:42 2019
From: mike_k_houghton at yahoo.co.uk (mike h)
Date: Thu, 14 Mar 2019 15:19:42 +0000
Subject: [Haskell-beginners] Matrix and types
In-Reply-To: <CAGSugssd0pPEERe7+3gy_MeHhvpRt=Vdp_v1oXqWYXeKQ87jNg@mail.gmail.com>
References: <F25F3321-F7AC-4B57-97F3-E4B340E10DC4@yahoo.co.uk>
 <20190314113720.xim35mdypfxxqpol@x60s.casa>
 <CAGSugssd0pPEERe7+3gy_MeHhvpRt=Vdp_v1oXqWYXeKQ87jNg@mail.gmail.com>
Message-ID: <EA0DDEE5-E4AA-44DC-B6E8-9F32D0E651AB@yahoo.co.uk>

Hi,
Thanks for the pointers. So I’ve got

data M (n :: Nat) a = M [a] deriving Show

t2 :: M 2 Int
t2  = M [1,2]

t3 :: M 3 Int
t3 = M [1,2,3]

fx :: Num a => M n a -> M n a -> M n a
fx (M xs) (M ys) = M (zipWith (+) xs ys)

and having 
g = fx t2 t3

won’t compile. Which is what I want.
However…

t2 :: M 2 Int
t2  = M [1,2]

is ‘hardwired’ to 2 and clearly I could make t2 return  a list of any length. 
So what I then tried to look at was a general function that would take a list of Int and create the M type using the length of the supplied list. 
In other words if I supply a list, xs, of length n then I wan’t  M n xs
Like this

createIntM xs = (M xs) :: M (length xs) Int

which compile and has type
λ-> :t createIntM 
createIntM :: [Int] -> M (length xs) Int

and all Ms created using createIntM  have the same type irrespective of the length of the supplied list.

What’s the type jiggery I need or is this not the right way to go?

Thanks

Mike




> On 14 Mar 2019, at 13:12, Frederic Cogny <frederic.cogny at gmail.com> wrote:
> 
> The (experimental) Static module of hmatrix seems (I've used the packaged but not that module) to do exactly that: http://hackage.haskell.org/package/hmatrix-0.19.0.0/docs/Numeric-LinearAlgebra-Static.html <http://hackage.haskell.org/package/hmatrix-0.19.0.0/docs/Numeric-LinearAlgebra-Static.html>
> 
> 
> 
> On Thu, Mar 14, 2019, 12:37 PM Francesco Ariis <fa-ml at ariis.it <mailto:fa-ml at ariis.it>> wrote:
> Hello Mike,
> 
> On Thu, Mar 14, 2019 at 11:10:06AM +0000, mike h wrote:
> > Multiplication of two matrices is only defined when the the number of columns in the first matrix 
> > equals the number of rows in the second matrix. i.e. c1 == r2
> > 
> > So when writing the multiplication function I can check that  c1 == r2 and do something.
> > However what I really want to do, if possible, is to have the compiler catch the error. 
> 
> Type-level literals [1] or any kind of similar trickery should help you
> with having matrices checked at compile-time.
> 
> [1] https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html <https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org <mailto:Beginners at haskell.org>
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners <http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners>
> -- 
> Frederic Cogny
> +33 7 83 12 61 69
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

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From frederic.cogny at gmail.com  Fri Mar 15 11:37:34 2019
From: frederic.cogny at gmail.com (Frederic Cogny)
Date: Fri, 15 Mar 2019 12:37:34 +0100
Subject: [Haskell-beginners] Matrix and types
In-Reply-To: <EA0DDEE5-E4AA-44DC-B6E8-9F32D0E651AB@yahoo.co.uk>
References: <F25F3321-F7AC-4B57-97F3-E4B340E10DC4@yahoo.co.uk>
 <20190314113720.xim35mdypfxxqpol@x60s.casa>
 <CAGSugssd0pPEERe7+3gy_MeHhvpRt=Vdp_v1oXqWYXeKQ87jNg@mail.gmail.com>
 <EA0DDEE5-E4AA-44DC-B6E8-9F32D0E651AB@yahoo.co.uk>
Message-ID: <CAGSugstdt3ert9TmTaxThhMas+BR66j-GZ3_CpT-EWomXcEUgA@mail.gmail.com>

I'm not sure I understand your question Mike.
Are you saying createIntM behaves as desired but the data constructor M
could let you build a data M with the wrong type. for instance M [1,2] :: M
1 Int ?

If that is your question, then one way to handle this is to have a separate
module where you define the data type and the proper constructor (here
M and createIntM) but where you do not expose the type constructor. so
something like

module MyModule
  ( M -- as opposed to M(..) to not expose the type constructor
  , createIntM
  ) where

Then, outside of MyModule, you can not create an incorrect lentgh annotated
list since the only way to build it is through createIntM

Does that make sense?

On Thu, Mar 14, 2019 at 4:19 PM mike h <mike_k_houghton at yahoo.co.uk> wrote:

> Hi,
> Thanks for the pointers. So I’ve got
>
> data M (n :: Nat) a = M [a] deriving Show
>
> t2 :: M 2 Int
> t2  = M [1,2]
>
> t3 :: M 3 Int
> t3 = M [1,2,3]
>
> fx :: Num a => M n a -> M n a -> M n a
> fx (M xs) (M ys) = M (zipWith (+) xs ys)
>
> and having
> g = fx t2 t3
>
> won’t compile. Which is what I want.
> However…
>
> t2 :: M 2 Int
> t2  = M [1,2]
>
> is ‘hardwired’ to 2 and clearly I could make t2 return  a list of
> any length.
> So what I then tried to look at was a general function that would take a
> list of Int and create the M type using the length of the supplied list.
> In other words if I supply a list, xs, of length n then I wan’t  M n xs
> Like this
>
> createIntM xs = (M xs) :: M (length xs) Int
>
> which compile and has type
> λ-> :t createIntM
> createIntM :: [Int] -> M (length xs) Int
>
> and all Ms created using createIntM  have the same type irrespective of
> the length of the supplied list.
>
> What’s the type jiggery I need or is this not the right way to go?
>
> Thanks
>
> Mike
>
>
>
>
> On 14 Mar 2019, at 13:12, Frederic Cogny <frederic.cogny at gmail.com> wrote:
>
> The (experimental) Static module of hmatrix seems (I've used the packaged
> but not that module) to do exactly that:
> http://hackage.haskell.org/package/hmatrix-0.19.0.0/docs/Numeric-LinearAlgebra-Static.html
>
>
>
> On Thu, Mar 14, 2019, 12:37 PM Francesco Ariis <fa-ml at ariis.it> wrote:
>
>> Hello Mike,
>>
>> On Thu, Mar 14, 2019 at 11:10:06AM +0000, mike h wrote:
>> > Multiplication of two matrices is only defined when the the number of
>> columns in the first matrix
>> > equals the number of rows in the second matrix. i.e. c1 == r2
>> >
>> > So when writing the multiplication function I can check that  c1 == r2
>> and do something.
>> > However what I really want to do, if possible, is to have the compiler
>> catch the error.
>>
>> Type-level literals [1] or any kind of similar trickery should help you
>> with having matrices checked at compile-time.
>>
>> [1]
>> https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
> --
> Frederic Cogny
> +33 7 83 12 61 69
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
> --
Frederic Cogny
+33 7 83 12 61 69
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From mike_k_houghton at yahoo.co.uk  Fri Mar 15 12:57:13 2019
From: mike_k_houghton at yahoo.co.uk (mike h)
Date: Fri, 15 Mar 2019 12:57:13 +0000
Subject: [Haskell-beginners] Matrix and types
In-Reply-To: <CAGSugstdt3ert9TmTaxThhMas+BR66j-GZ3_CpT-EWomXcEUgA@mail.gmail.com>
References: <F25F3321-F7AC-4B57-97F3-E4B340E10DC4@yahoo.co.uk>
 <20190314113720.xim35mdypfxxqpol@x60s.casa>
 <CAGSugssd0pPEERe7+3gy_MeHhvpRt=Vdp_v1oXqWYXeKQ87jNg@mail.gmail.com>
 <EA0DDEE5-E4AA-44DC-B6E8-9F32D0E651AB@yahoo.co.uk>
 <CAGSugstdt3ert9TmTaxThhMas+BR66j-GZ3_CpT-EWomXcEUgA@mail.gmail.com>
Message-ID: <542C66B8-2502-4A2D-92C2-7AC382FAAF98@yahoo.co.uk>


Hi Frederic,

Yeh, my explanation is a bit dubious :) 
What I’m trying to say is:
Looking at the type M (n::Nat) 
If I want an M 2  of Ints say,  then I need to write the function with signature

 f :: M 2 Int
 

If I want a M 3 then I need to explicitly write the function with signature
M 3 Int

and so on for every possible instance that I might want.

What I would like to do is have just one function that is somehow parameterised to create the M tagged with the required value of (n::Nat)
In pseudo Haskell

create :: Int -> [Int] -> M n 
create size ns = (M ns) ::  M size Int

where  its trying to coerce (M ns) into the type (M size Int) where size is an Int but needs to be a Nat.

It’s sort of like parameterising the signature of the function.

Thanks

Mike

> On 15 Mar 2019, at 11:37, Frederic Cogny <frederic.cogny at gmail.com> wrote:
> 
> I'm not sure I understand your question Mike.
> Are you saying createIntM behaves as desired but the data constructor M could let you build a data M with the wrong type. for instance M [1,2] :: M 1 Int ?
> 
> If that is your question, then one way to handle this is to have a separate module where you define the data type and the proper constructor (here M and createIntM) but where you do not expose the type constructor. so something like
> 
> module MyModule
>   ( M -- as opposed to M(..) to not expose the type constructor
>   , createIntM
>   ) where
> 
> Then, outside of MyModule, you can not create an incorrect lentgh annotated list since the only way to build it is through createIntM
> 
> Does that make sense?
> 
> On Thu, Mar 14, 2019 at 4:19 PM mike h <mike_k_houghton at yahoo.co.uk <mailto:mike_k_houghton at yahoo.co.uk>> wrote:
> Hi,
> Thanks for the pointers. So I’ve got
> 
> data M (n :: Nat) a = M [a] deriving Show
> 
> t2 :: M 2 Int
> t2  = M [1,2]
> 
> t3 :: M 3 Int
> t3 = M [1,2,3]
> 
> fx :: Num a => M n a -> M n a -> M n a
> fx (M xs) (M ys) = M (zipWith (+) xs ys)
> 
> and having 
> g = fx t2 t3
> 
> won’t compile. Which is what I want.
> However…
> 
> t2 :: M 2 Int
> t2  = M [1,2]
> 
> is ‘hardwired’ to 2 and clearly I could make t2 return  a list of any length. 
> So what I then tried to look at was a general function that would take a list of Int and create the M type using the length of the supplied list. 
> In other words if I supply a list, xs, of length n then I wan’t  M n xs
> Like this
> 
> createIntM xs = (M xs) :: M (length xs) Int
> 
> which compile and has type
> λ-> :t createIntM 
> createIntM :: [Int] -> M (length xs) Int
> 
> and all Ms created using createIntM  have the same type irrespective of the length of the supplied list.
> 
> What’s the type jiggery I need or is this not the right way to go?
> 
> Thanks
> 
> Mike
> 
> 
> 
> 
>> On 14 Mar 2019, at 13:12, Frederic Cogny <frederic.cogny at gmail.com <mailto:frederic.cogny at gmail.com>> wrote:
>> 
>> The (experimental) Static module of hmatrix seems (I've used the packaged but not that module) to do exactly that: http://hackage.haskell.org/package/hmatrix-0.19.0.0/docs/Numeric-LinearAlgebra-Static.html <http://hackage.haskell.org/package/hmatrix-0.19.0.0/docs/Numeric-LinearAlgebra-Static.html>
>> 
>> 
>> 
>> On Thu, Mar 14, 2019, 12:37 PM Francesco Ariis <fa-ml at ariis.it <mailto:fa-ml at ariis.it>> wrote:
>> Hello Mike,
>> 
>> On Thu, Mar 14, 2019 at 11:10:06AM +0000, mike h wrote:
>> > Multiplication of two matrices is only defined when the the number of columns in the first matrix 
>> > equals the number of rows in the second matrix. i.e. c1 == r2
>> > 
>> > So when writing the multiplication function I can check that  c1 == r2 and do something.
>> > However what I really want to do, if possible, is to have the compiler catch the error. 
>> 
>> Type-level literals [1] or any kind of similar trickery should help you
>> with having matrices checked at compile-time.
>> 
>> [1] https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html <https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html>
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org <mailto:Beginners at haskell.org>
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners <http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners>
>> -- 
>> Frederic Cogny
>> +33 7 83 12 61 69
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org <mailto:Beginners at haskell.org>
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners <http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners>
> 
> -- 
> Frederic Cogny
> +33 7 83 12 61 69

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From sylvain at haskus.fr  Fri Mar 15 13:48:06 2019
From: sylvain at haskus.fr (Sylvain Henry)
Date: Fri, 15 Mar 2019 14:48:06 +0100
Subject: [Haskell-beginners] Matrix and types
In-Reply-To: <542C66B8-2502-4A2D-92C2-7AC382FAAF98@yahoo.co.uk>
References: <F25F3321-F7AC-4B57-97F3-E4B340E10DC4@yahoo.co.uk>
 <20190314113720.xim35mdypfxxqpol@x60s.casa>
 <CAGSugssd0pPEERe7+3gy_MeHhvpRt=Vdp_v1oXqWYXeKQ87jNg@mail.gmail.com>
 <EA0DDEE5-E4AA-44DC-B6E8-9F32D0E651AB@yahoo.co.uk>
 <CAGSugstdt3ert9TmTaxThhMas+BR66j-GZ3_CpT-EWomXcEUgA@mail.gmail.com>
 <542C66B8-2502-4A2D-92C2-7AC382FAAF98@yahoo.co.uk>
Message-ID: <cf5dda23-bd3a-a05c-b353-ce3ee79ad2e8@haskus.fr>

Hi,

The problem is that Haskell lists don't carry their length in their type 
hence you cannot enforce their length at compile time. But you can 
define your M this way instead:

{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE KindSignatures #-}

import GHC.TypeNats
import Data.Proxy

data M (n :: Nat) a where
    MNil  :: M 0 a
    MCons :: a -> M (n-1) a -> M n a

infixr 5 `MCons`

toList :: M k a -> [a]
toList MNil         = []
toList (MCons a as) = a:toList as

instance (KnownNat n, Show a) => Show (M n a) where
    show xs = mconcat
       [ "M @"
       , show (natVal (Proxy :: Proxy n))
       , " "
       , show (toList xs)
       ]

--t2 :: M 2 Integer
t2 = 1 `MCons` 2 `MCons` MNil

--t3 :: M 3 Integer
t3 = 1 `MCons` 2 `MCons` 3 `MCons` MNil

zipM :: (a -> b -> c) -> M n a -> M n b -> M n c
zipM _f MNil         MNil         = MNil
zipM  f (MCons a as) (MCons b bs) = MCons (f a b) (zipM f as bs)

fx :: Num a => M n a -> M n a -> M n a
fx = zipM (+)

Test:

 > t2
M @2 [1,2]
 > fx t2 t2
M @2 [2,4]
 > fx t2 t3

<interactive>:38:7: error:
     • Couldn't match type ‘3’ with ‘2’
       Expected type: M 2 Integer
         Actual type: M 3 Integer


Cheers,
Sylvain


On 15/03/2019 13:57, mike h wrote:
>
> Hi Frederic,
>
> Yeh, my explanation is a bit dubious :)
> What I’m trying to say is:
> Looking at the type M (n::Nat)
> If I want an M 2  of Ints say,  then I need to write the function with 
> signature
>
>  f :: M 2 Int
>
> If I want a M 3 then I need to explicitly write the function with 
> signature
> M 3 Int
>
> and so on for every possible instance that I might want.
>
> What I would like to do is have just one function that is somehow 
> parameterised to create the M tagged with the required value of (n::Nat)
> In pseudo Haskell
>
> create :: Int -> [Int] -> M n
> create size ns = (M ns) ::  M size Int
>
> where  its trying to coerce (M ns) into the type (M size Int) where 
> size is an Int but needs to be a Nat.
>
> It’s sort of like parameterising the signature of the function.
>
> Thanks
>
> Mike
>
>> On 15 Mar 2019, at 11:37, Frederic Cogny <frederic.cogny at gmail.com 
>> <mailto:frederic.cogny at gmail.com>> wrote:
>>
>> I'm not sure I understand your question Mike.
>> Are you saying createIntM behaves as desired but the data constructor 
>> M could let you build a data M with the wrong type. for instance M 
>> [1,2] :: M 1 Int ?
>>
>> If that is your question, then one way to handle this is to have a 
>> separate module where you define the data type and the proper 
>> constructor (here M and createIntM) but where you do not expose the 
>> type constructor. so something like
>>
>> module MyModule
>>   ( M -- as opposed to M(..) to not expose the type constructor
>> , createIntM
>>   ) where
>>
>> Then, outside of MyModule, you can not create an incorrect lentgh 
>> annotated list since the only way to build it is through createIntM
>>
>> Does that make sense?
>>
>> On Thu, Mar 14, 2019 at 4:19 PM mike h <mike_k_houghton at yahoo.co.uk 
>> <mailto:mike_k_houghton at yahoo.co.uk>> wrote:
>>
>>     Hi,
>>     Thanks for the pointers. So I’ve got
>>
>>     data M (n :: Nat) a = M [a] deriving Show
>>
>>     t2 :: M 2 Int
>>     t2  = M [1,2]
>>
>>     t3 :: M 3 Int
>>     t3 = M [1,2,3]
>>
>>     fx :: Num a => M n a -> M n a -> M n a
>>     fx (M xs) (M ys) = M (zipWith (+) xs ys)
>>
>>     and having
>>     g = fx t2 t3
>>
>>     won’t compile. Which is what I want.
>>     However…
>>
>>     t2::M 2 Int
>>     t2 =M [1,2]
>>
>>     is ‘hardwired’ to 2 and clearly I could make t2 return  a list of
>>     any length.
>>     So what I then tried to look at was a general function that would
>>     take a list of Int and create the M type using the length of
>>     the supplied list.
>>     In other words if I supply a list, xs, of length n then I wan’t
>>      M n xs
>>     Like this
>>
>>     createIntM xs = (M xs) ::M (lengthxs) Int
>>
>>     which compile and has type
>>     λ-> :t createIntM
>>     createIntM :: [Int] -> M (length xs) Int
>>
>>     and all Ms created using createIntM  have the same type
>>     irrespective of the length of the supplied list.
>>
>>     What’s the type jiggery I need or is this not the right way to go?
>>
>>     Thanks
>>
>>     Mike
>>
>>
>>
>>
>>>     On 14 Mar 2019, at 13:12, Frederic Cogny
>>>     <frederic.cogny at gmail.com <mailto:frederic.cogny at gmail.com>> wrote:
>>>
>>>     The (experimental) Static module of hmatrix seems (I've used the
>>>     packaged but not that module) to do exactly that:
>>>     http://hackage.haskell.org/package/hmatrix-0.19.0.0/docs/Numeric-LinearAlgebra-Static.html
>>>
>>>
>>>
>>>
>>>     On Thu, Mar 14, 2019, 12:37 PM Francesco Ariis <fa-ml at ariis.it
>>>     <mailto:fa-ml at ariis.it>> wrote:
>>>
>>>         Hello Mike,
>>>
>>>         On Thu, Mar 14, 2019 at 11:10:06AM +0000, mike h wrote:
>>>         > Multiplication of two matrices is only defined when the
>>>         the number of columns in the first matrix
>>>         > equals the number of rows in the second matrix. i.e. c1 == r2
>>>         >
>>>         > So when writing the multiplication function I can check
>>>         that  c1 == r2 and do something.
>>>         > However what I really want to do, if possible, is to have
>>>         the compiler catch the error.
>>>
>>>         Type-level literals [1] or any kind of similar trickery
>>>         should help you
>>>         with having matrices checked at compile-time.
>>>
>>>         [1]
>>>         https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html
>>>         _______________________________________________
>>>         Beginners mailing list
>>>         Beginners at haskell.org <mailto:Beginners at haskell.org>
>>>         http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>>
>>>     -- 
>>>     Frederic Cogny
>>>     +33 7 83 12 61 69
>>>     _______________________________________________
>>>     Beginners mailing list
>>>     Beginners at haskell.org <mailto:Beginners at haskell.org>
>>>     http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>> -- 
>> Frederic Cogny
>> +33 7 83 12 61 69
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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From mike_k_houghton at yahoo.co.uk  Fri Mar 15 20:44:46 2019
From: mike_k_houghton at yahoo.co.uk (mike h)
Date: Fri, 15 Mar 2019 20:44:46 +0000
Subject: [Haskell-beginners] Matrix and types
In-Reply-To: <cf5dda23-bd3a-a05c-b353-ce3ee79ad2e8@haskus.fr>
References: <F25F3321-F7AC-4B57-97F3-E4B340E10DC4@yahoo.co.uk>
 <20190314113720.xim35mdypfxxqpol@x60s.casa>
 <CAGSugssd0pPEERe7+3gy_MeHhvpRt=Vdp_v1oXqWYXeKQ87jNg@mail.gmail.com>
 <EA0DDEE5-E4AA-44DC-B6E8-9F32D0E651AB@yahoo.co.uk>
 <CAGSugstdt3ert9TmTaxThhMas+BR66j-GZ3_CpT-EWomXcEUgA@mail.gmail.com>
 <542C66B8-2502-4A2D-92C2-7AC382FAAF98@yahoo.co.uk>
 <cf5dda23-bd3a-a05c-b353-ce3ee79ad2e8@haskus.fr>
Message-ID: <0E90C918-DC68-4D92-AF80-44F09CFE1B7B@yahoo.co.uk>

Thanks.

> On 15 Mar 2019, at 13:48, Sylvain Henry <sylvain at haskus.fr> wrote:
> 
> Hi,
> 
> The problem is that Haskell lists don't carry their length in their type hence you cannot enforce their length at compile time. But you can define your M this way instead:
> 
> {-# LANGUAGE TypeOperators #-}
> {-# LANGUAGE GADTs #-}
> {-# LANGUAGE DataKinds #-}
> {-# LANGUAGE ScopedTypeVariables #-}
> {-# LANGUAGE KindSignatures #-}
> 
> import GHC.TypeNats
> import Data.Proxy
> 
> data M (n :: Nat) a where
>    MNil  :: M 0 a
>    MCons :: a -> M (n-1) a -> M n a
> 
> infixr 5 `MCons`
> 
> toList :: M k a -> [a]
> toList MNil         = []
> toList (MCons a as) = a:toList as
> 
> instance (KnownNat n, Show a) => Show (M n a) where
>    show xs = mconcat
>       [ "M @"
>       , show (natVal (Proxy :: Proxy n))
>       , " "
>       , show (toList xs)
>       ]
> 
> --t2 :: M 2 Integer
> t2 = 1 `MCons` 2 `MCons` MNil
> 
> --t3 :: M 3 Integer
> t3 = 1 `MCons` 2 `MCons` 3 `MCons` MNil
> 
> zipM :: (a -> b -> c) -> M n a -> M n b -> M n c
> zipM _f MNil         MNil         = MNil
> zipM  f (MCons a as) (MCons b bs) = MCons (f a b) (zipM f as bs) 
> 
> fx :: Num a => M n a -> M n a -> M n a
> fx = zipM (+)
> 
> 
> Test:
> 
> > t2
> M @2 [1,2]
> > fx t2 t2
> M @2 [2,4]
> > fx t2 t3
> 
> <interactive>:38:7: error:
>     • Couldn't match type ‘3’ with ‘2’
>       Expected type: M 2 Integer
>         Actual type: M 3 Integer
> 
> 
> 
> Cheers,
> Sylvain
> 
> 
> 
> On 15/03/2019 13:57, mike h wrote:
>> 
>> Hi Frederic,
>> 
>> Yeh, my explanation is a bit dubious :) 
>> What I’m trying to say is:
>> Looking at the type M (n::Nat) 
>> If I want an M 2  of Ints say,  then I need to write the function with signature
>> 
>>  f :: M 2 Int
>>  
>> 
>> If I want a M 3 then I need to explicitly write the function with signature
>> M 3 Int
>> 
>> and so on for every possible instance that I might want.
>> 
>> What I would like to do is have just one function that is somehow parameterised to create the M tagged with the required value of (n::Nat)
>> In pseudo Haskell
>> 
>> create :: Int -> [Int] -> M n 
>> create size ns = (M ns) ::  M size Int
>> 
>> where  its trying to coerce (M ns) into the type (M size Int) where size is an Int but needs to be a Nat.
>> 
>> It’s sort of like parameterising the signature of the function.
>> 
>> Thanks
>> 
>> Mike
>> 
>>> On 15 Mar 2019, at 11:37, Frederic Cogny <frederic.cogny at gmail.com <mailto:frederic.cogny at gmail.com>> wrote:
>>> 
>>> I'm not sure I understand your question Mike.
>>> Are you saying createIntM behaves as desired but the data constructor M could let you build a data M with the wrong type. for instance M [1,2] :: M 1 Int ?
>>> 
>>> If that is your question, then one way to handle this is to have a separate module where you define the data type and the proper constructor (here M and createIntM) but where you do not expose the type constructor. so something like
>>> 
>>> module MyModule
>>>   ( M -- as opposed to M(..) to not expose the type constructor
>>>   , createIntM
>>>   ) where
>>> 
>>> Then, outside of MyModule, you can not create an incorrect lentgh annotated list since the only way to build it is through createIntM
>>> 
>>> Does that make sense?
>>> 
>>> On Thu, Mar 14, 2019 at 4:19 PM mike h <mike_k_houghton at yahoo.co.uk <mailto:mike_k_houghton at yahoo.co.uk>> wrote:
>>> Hi,
>>> Thanks for the pointers. So I’ve got
>>> 
>>> data M (n :: Nat) a = M [a] deriving Show
>>> 
>>> t2 :: M 2 Int
>>> t2  = M [1,2]
>>> 
>>> t3 :: M 3 Int
>>> t3 = M [1,2,3]
>>> 
>>> fx :: Num a => M n a -> M n a -> M n a
>>> fx (M xs) (M ys) = M (zipWith (+) xs ys)
>>> 
>>> and having 
>>> g = fx t2 t3
>>> 
>>> won’t compile. Which is what I want.
>>> However…
>>> 
>>> t2 :: M 2 Int
>>> t2  = M [1,2]
>>> 
>>> is ‘hardwired’ to 2 and clearly I could make t2 return  a list of any length. 
>>> So what I then tried to look at was a general function that would take a list of Int and create the M type using the length of the supplied list. 
>>> In other words if I supply a list, xs, of length n then I wan’t  M n xs
>>> Like this
>>> 
>>> createIntM xs = (M xs) :: M (length xs) Int
>>> 
>>> which compile and has type
>>> λ-> :t createIntM 
>>> createIntM :: [Int] -> M (length xs) Int
>>> 
>>> and all Ms created using createIntM  have the same type irrespective of the length of the supplied list.
>>> 
>>> What’s the type jiggery I need or is this not the right way to go?
>>> 
>>> Thanks
>>> 
>>> Mike
>>> 
>>> 
>>> 
>>> 
>>>> On 14 Mar 2019, at 13:12, Frederic Cogny <frederic.cogny at gmail.com <mailto:frederic.cogny at gmail.com>> wrote:
>>>> 
>>>> The (experimental) Static module of hmatrix seems (I've used the packaged but not that module) to do exactly that: http://hackage.haskell.org/package/hmatrix-0.19.0.0/docs/Numeric-LinearAlgebra-Static.html <http://hackage.haskell.org/package/hmatrix-0.19.0.0/docs/Numeric-LinearAlgebra-Static.html>
>>>> 
>>>> 
>>>> 
>>>> On Thu, Mar 14, 2019, 12:37 PM Francesco Ariis <fa-ml at ariis.it <mailto:fa-ml at ariis.it>> wrote:
>>>> Hello Mike,
>>>> 
>>>> On Thu, Mar 14, 2019 at 11:10:06AM +0000, mike h wrote:
>>>> > Multiplication of two matrices is only defined when the the number of columns in the first matrix 
>>>> > equals the number of rows in the second matrix. i.e. c1 == r2
>>>> > 
>>>> > So when writing the multiplication function I can check that  c1 == r2 and do something.
>>>> > However what I really want to do, if possible, is to have the compiler catch the error. 
>>>> 
>>>> Type-level literals [1] or any kind of similar trickery should help you
>>>> with having matrices checked at compile-time.
>>>> 
>>>> [1] https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html <https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html>
>>>> _______________________________________________
>>>> Beginners mailing list
>>>> Beginners at haskell.org <mailto:Beginners at haskell.org>
>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners <http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners>
>>>> -- 
>>>> Frederic Cogny
>>>> +33 7 83 12 61 69
>>>> _______________________________________________
>>>> Beginners mailing list
>>>> Beginners at haskell.org <mailto:Beginners at haskell.org>
>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners <http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners>
>>> 
>>> -- 
>>> Frederic Cogny
>>> +33 7 83 12 61 69
>> 
>> 
>> 
>> _______________________________________________
>> Beginners mailing list
>> Beginners at haskell.org <mailto:Beginners at haskell.org>
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners <http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

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From jaysinhp at gmail.com  Sun Mar 17 08:22:11 2019
From: jaysinhp at gmail.com (Jaysinh shukla)
Date: Sun, 17 Mar 2019 13:52:11 +0530
Subject: [Haskell-beginners] Learn you a Haskell for great good! group
	reading session
Message-ID: <CAPPZTOH=5XBSgzDs3ooRHNeNZ_hEi1fd7OZ7kBbP6fvj++D_1g@mail.gmail.com>

Respected Member,

    I am trying to learn Haskell from the book Learn you a Haskell for
great good! [1]. I livestream my reading sessions at this [2] Twitch
channel. Group reading is helping me to learn better. It is way more
productive than reading alone. If you are learning Haskell, please
join us. If you already know Haskell, please join to teach. Teaching
will give you a good revision. Don't worry about the commitment to
attend each and every session. It is fine to attend sessions on the
day you are available and skip the rest. The fun part is, all the
sessions will be on weekends. You can watch videos of past sessions
here [3]. I am trying to maintain an event calendar for upcoming
sessions here [4]. Please share these resources with whoever learning
the Haskell. Don't hesitate to ask your questions here or in a
personal mail. Thanks!

1: http://learnyouahaskell.com
2: https://www.twitch.tv/jaysinhp
3: https://www.twitch.tv/jaysinhp/videos
4: https://www.twitch.tv/jaysinhp/events

From mlang at delysid.org  Wed Mar 27 01:08:15 2019
From: mlang at delysid.org (Mario Lang)
Date: Wed, 27 Mar 2019 02:08:15 +0100
Subject: [Haskell-beginners] A sort of fold for bits
Message-ID: <87bm1xjf9c.fsf@fx.blind.guru>

Hi.

I have written the following function for "iterating" over all set bits
in a Bits instance:

foldBits :: (Bits bits, Num bits) => (a -> Int -> a) -> a -> bits -> a
foldBits _ a 0 = a
foldBits f a n = foldBits f (f a lsb) (n `clearBit` lsb) where
  lsb = countTrailingZeros n

The type signature mimmicks foldl.
However, composing several calls to foldBits ends up pretty messy:

foldBits f (foldBits f (foldBits f [] value1) value2) value3

So I was thinking, maybe I should just flip the final arguments to make
composition easier:

fooBits :: (Bits bits, Num bits) => (a -> Int -> a) -> bits -> a ->  a
fooBits _ 0 a = a
foldBits f n a = foldBits f (n `clearBit` lsb) (f a lsb) where
  lsb = countTrailingZeros n

fooBits f value3 . fooBits f value2 . fooBits f value1 $ []

This looks more tidy.  However, now that I am no longer mimmicking
foldl, I am sort of at a loss how to name this beast.

iterBits comes to bind, but this isn't really like iterate.

I know, this question might look silly, but good naming conventions seem
to make it easier for me to reason about the code.

Any suggestions?

P.S.: Mimmicking foldl is probably wrong as well, since this isn't
really a fold, is it?

-- 
CYa,
  ⡍⠁⠗⠊⠕

From kothariyugesh at gmail.com  Wed Mar 27 03:35:14 2019
From: kothariyugesh at gmail.com (Yugesh Kothari)
Date: Wed, 27 Mar 2019 09:05:14 +0530
Subject: [Haskell-beginners] IO String and String using readFile
Message-ID: <CACSi4wB3egUHgv_NGcR4hCQ_2aH=3QGSwr-FpQN1W5m5FDY2SQ@mail.gmail.com>

Hi,

I am trying to read data from a file.
When I do-
ghci> contents <- readFile "file.txt"
ghci> words contents

Then everything works.

The same thing when done in a .hs file gives an IO String vs [String] error.

Why is that so?
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From ian at zenhack.net  Wed Mar 27 03:40:36 2019
From: ian at zenhack.net (Ian Denhardt)
Date: Tue, 26 Mar 2019 23:40:36 -0400
Subject: [Haskell-beginners] IO String and String using readFile
In-Reply-To: <CACSi4wB3egUHgv_NGcR4hCQ_2aH=3QGSwr-FpQN1W5m5FDY2SQ@mail.gmail.com>
References: <CACSi4wB3egUHgv_NGcR4hCQ_2aH=3QGSwr-FpQN1W5m5FDY2SQ@mail.gmail.com>
Message-ID: <155365803596.1175.5211347879418303338@localhost.localdomain>

It would help to see the complete source file, but I'll hazard a guess
you're doing something like:

main = do
    contents <- readFile "file.txt"
    words contents

At the GHCi prompt, each line can be any expression, and GHCi will
evaluate it and then display it. The two lines in your session aren't
really related.

In contrast, the do block in the source file expects the expression at
the end to be an IO action.

What do you want your program to do when you get to "words contents"?
display it? (If you want to display it, pass it to `print`).

Quoting Yugesh Kothari (2019-03-26 23:35:14)
>    Hi,�
>    I am trying to read data from a file.
>    When I do-
>    ghci> contents <- readFile "file.txt"
>    ghci> words contents
>    Then everything works.
>    The same thing when done in a .hs file gives an IO String vs [String]
>    error.
>    Why is that so?

From kothariyugesh at gmail.com  Wed Mar 27 03:48:35 2019
From: kothariyugesh at gmail.com (Yugesh Kothari)
Date: Wed, 27 Mar 2019 09:18:35 +0530
Subject: [Haskell-beginners] IO String and String using readFile
In-Reply-To: <155365803596.1175.5211347879418303338@localhost.localdomain>
References: <CACSi4wB3egUHgv_NGcR4hCQ_2aH=3QGSwr-FpQN1W5m5FDY2SQ@mail.gmail.com>
 <155365803596.1175.5211347879418303338@localhost.localdomain>
Message-ID: <CACSi4wAraWef9mVHuk-BpAiRg5OvsE_4Cy4j+ebT3=ExWBJo0Q@mail.gmail.com>

I see. anyway, my use case is something like this-

I have two functions
fromFile :: [String] -> [Int]
func :: String -> [Int]

I want to use the "words contents" output and pass each element in it to
func and send back [Int] from "fromFile" function (where I originally read
the file.)

Could you suggest a better way to do this?

Quoting Ian Denhardt


On Wed, 27 Mar, 2019, 9:13 AM Ian Denhardt, <ian at zenhack.net> wrote:

> It would help to see the complete source file, but I'll hazard a guess
> you're doing something like:
>
> main = do
>     contents <- readFile "file.txt"
>     words contents
>
> At the GHCi prompt, each line can be any expression, and GHCi will
> evaluate it and then display it. The two lines in your session aren't
> really related.
>
> In contrast, the do block in the source file expects the expression at
> the end to be an IO action.
>
> What do you want your program to do when you get to "words contents"?
> display it? (If you want to display it, pass it to `print`).
>
> Quoting Yugesh Kothari (2019-03-26 23:35:14)
> >    Hi,�
> >    I am trying to read data from a file.
> >    When I do-
> >    ghci> contents <- readFile "file.txt"
> >    ghci> words contents
> >    Then everything works.
> >    The same thing when done in a .hs file gives an IO String vs [String]
> >    error.
> >    Why is that so?
>
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From tanuki at gmail.com  Wed Mar 27 03:49:39 2019
From: tanuki at gmail.com (Theodore Lief Gannon)
Date: Tue, 26 Mar 2019 20:49:39 -0700
Subject: [Haskell-beginners] IO String and String using readFile
In-Reply-To: <CACSi4wB3egUHgv_NGcR4hCQ_2aH=3QGSwr-FpQN1W5m5FDY2SQ@mail.gmail.com>
References: <CACSi4wB3egUHgv_NGcR4hCQ_2aH=3QGSwr-FpQN1W5m5FDY2SQ@mail.gmail.com>
Message-ID: <CAJoPsuB2ssg0du_7eOO0fjmikr1pvFsO9u9XC+_t84CQHp8hbg@mail.gmail.com>

I'm guessing in the .hs file, you have this in a do block? Something like:

foo = do
    contents <- readFile
    words contents

If so, the problem is the return type of `words`. Each line of the do block
has to have an IO value, and words is a pure function. To lift its result
into the monad, use the aptly-named `pure` function:

foo = do
    contents <- readFile
    pure $ words contents


On Tue, Mar 26, 2019, 8:35 PM Yugesh Kothari <kothariyugesh at gmail.com>
wrote:

> Hi,
>
> I am trying to read data from a file.
> When I do-
> ghci> contents <- readFile "file.txt"
> ghci> words contents
>
> Then everything works.
>
> The same thing when done in a .hs file gives an IO String vs [String]
> error.
>
> Why is that so?
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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From kothariyugesh at gmail.com  Wed Mar 27 03:54:40 2019
From: kothariyugesh at gmail.com (Yugesh Kothari)
Date: Wed, 27 Mar 2019 09:24:40 +0530
Subject: [Haskell-beginners] Fwd:  IO String and String using readFile
In-Reply-To: <CACSi4wAraWef9mVHuk-BpAiRg5OvsE_4Cy4j+ebT3=ExWBJo0Q@mail.gmail.com>
References: <CACSi4wB3egUHgv_NGcR4hCQ_2aH=3QGSwr-FpQN1W5m5FDY2SQ@mail.gmail.com>
 <155365803596.1175.5211347879418303338@localhost.localdomain>
 <CACSi4wAraWef9mVHuk-BpAiRg5OvsE_4Cy4j+ebT3=ExWBJo0Q@mail.gmail.com>
Message-ID: <CACSi4wBCr7_PKto0s-OS+z4iFNjFO75eOHtZQmTuwCFY1=ZVew@mail.gmail.com>

Extremely sorry,

The definition of fromFile is String -> [Int] where input parameter is the
name of the file.

---------- Forwarded message ---------
From: Yugesh Kothari <kothariyugesh at gmail.com>
Date: Wed, 27 Mar, 2019, 9:18 AM
Subject: Re: [Haskell-beginners] IO String and String using readFile
To:
Cc: <beginners at haskell.org>


I see. anyway, my use case is something like this-

I have two functions
fromFile :: [String] -> [Int]
func :: String -> [Int]

I want to use the "words contents" output and pass each element in it to
func and send back [Int] from "fromFile" function (where I originally read
the file.)

Could you suggest a better way to do this?

Quoting Ian Denhardt


On Wed, 27 Mar, 2019, 9:13 AM Ian Denhardt, <ian at zenhack.net> wrote:

> It would help to see the complete source file, but I'll hazard a guess
> you're doing something like:
>
> main = do
>     contents <- readFile "file.txt"
>     words contents
>
> At the GHCi prompt, each line can be any expression, and GHCi will
> evaluate it and then display it. The two lines in your session aren't
> really related.
>
> In contrast, the do block in the source file expects the expression at
> the end to be an IO action.
>
> What do you want your program to do when you get to "words contents"?
> display it? (If you want to display it, pass it to `print`).
>
> Quoting Yugesh Kothari (2019-03-26 23:35:14)
> >    Hi,�
> >    I am trying to read data from a file.
> >    When I do-
> >    ghci> contents <- readFile "file.txt"
> >    ghci> words contents
> >    Then everything works.
> >    The same thing when done in a .hs file gives an IO String vs [String]
> >    error.
> >    Why is that so?
>
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From ian at zenhack.net  Wed Mar 27 03:57:13 2019
From: ian at zenhack.net (Ian Denhardt)
Date: Tue, 26 Mar 2019 23:57:13 -0400
Subject: [Haskell-beginners] IO String and String using readFile
In-Reply-To: <CACSi4wAraWef9mVHuk-BpAiRg5OvsE_4Cy4j+ebT3=ExWBJo0Q@mail.gmail.com>
References: <CACSi4wB3egUHgv_NGcR4hCQ_2aH=3QGSwr-FpQN1W5m5FDY2SQ@mail.gmail.com>
 <155365803596.1175.5211347879418303338@localhost.localdomain>
 <CACSi4wAraWef9mVHuk-BpAiRg5OvsE_4Cy4j+ebT3=ExWBJo0Q@mail.gmail.com>
Message-ID: <155365903334.2487.7573599623212981998@localhost.localdomain>

Sounds like you want concatMap:

    https://hackage.haskell.org/package/base-4.12.0.0/docs/Prelude.html#v:concatMap

Quoting Yugesh Kothari (2019-03-26 23:48:35)
>    I see. anyway, my use case is something like this-
>    I have two functions
>    fromFile :: [String] -> [Int]
>    func :: String -> [Int]
>    I want to use the "words contents" output and pass each element in it
>    to func and send back [Int] from "fromFile" function (where I
>    originally read the file.)
>    Could you suggest a better way to do this?
>    Quoting� Ian Denhardt
>    On Wed, 27 Mar, 2019, 9:13 AM Ian Denhardt, <[1]ian at zenhack.net> wrote:
>
>      It would help to see the complete source file, but I'll hazard a
>      guess
>      you're doing something like:
>      main = do
>      �  �  contents <- readFile "file.txt"
>      �  �  words contents
>      At the GHCi prompt, each line can be any expression, and GHCi will
>      evaluate it and then display it. The two lines in your session
>      aren't
>      really related.
>      In contrast, the do block in the source file expects the expression
>      at
>      the end to be an IO action.
>      What do you want your program to do when you get to "words
>      contents"?
>      display it? (If you want to display it, pass it to `print`).
>      Quoting Yugesh Kothari (2019-03-26 23:35:14)
>      >�  �  Hi,�
>      >�  �  I am trying to read data from a file.
>      >�  �  When I do-
>      >�  �  ghci> contents <- readFile "file.txt"
>      >�  �  ghci> words contents
>      >�  �  Then everything works.
>      >�  �  The same thing when done in a .hs file gives an IO String vs
>      [String]
>      >�  �  error.
>      >�  �  Why is that so?
>
> Verweise
>
>    1. mailto:ian at zenhack.net

From ian at zenhack.net  Wed Mar 27 04:02:49 2019
From: ian at zenhack.net (Ian Denhardt)
Date: Wed, 27 Mar 2019 00:02:49 -0400
Subject: [Haskell-beginners] Fwd:  IO String and String using readFile
In-Reply-To: <CACSi4wBCr7_PKto0s-OS+z4iFNjFO75eOHtZQmTuwCFY1=ZVew@mail.gmail.com>
References: <CACSi4wB3egUHgv_NGcR4hCQ_2aH=3QGSwr-FpQN1W5m5FDY2SQ@mail.gmail.com>
 <155365803596.1175.5211347879418303338@localhost.localdomain>
 <CACSi4wAraWef9mVHuk-BpAiRg5OvsE_4Cy4j+ebT3=ExWBJo0Q@mail.gmail.com>
 <CACSi4wBCr7_PKto0s-OS+z4iFNjFO75eOHtZQmTuwCFY1=ZVew@mail.gmail.com>
Message-ID: <155365936937.2487.14589775321104928555@localhost.localdomain>

Ah, in that case you'll need the type to be

    String -> IO [Int]

In Haskell, functions *only* do computation -- no side effects, like
reading a file. So a String -> [Int] can't do what you want. We have a
separate type, IO, for doing things that affect the outside world. For
example:

ghci> :type readFile
readFile :: FilePath -> IO String

Also, just a style tip: there's a type alias for String defined called
FilePath, which would make the type signature more clear in this case.

Quoting Yugesh Kothari (2019-03-26 23:54:40)
>    Extremely sorry,
>    The definition of fromFile is String -> [Int] where input parameter is
>    the name of the file.
>    ---------- Forwarded message ---------
>    From: Yugesh Kothari <[1]kothariyugesh at gmail.com>
>    Date: Wed, 27 Mar, 2019, 9:18 AM
>    Subject: Re: [Haskell-beginners] IO String and String using readFile
>    To:
>    Cc: <[2]beginners at haskell.org>
>    I see. anyway, my use case is something like this-
>    I have two functions
>    fromFile :: [String] -> [Int]
>    func :: String -> [Int]
>    I want to use the "words contents" output and pass each element in it
>    to func and send back [Int] from "fromFile" function (where I
>    originally read the file.)
>    Could you suggest a better way to do this?
>    Quoting� Ian Denhardt
>    On Wed, 27 Mar, 2019, 9:13 AM Ian Denhardt, <[3]ian at zenhack.net> wrote:
>
>      It would help to see the complete source file, but I'll hazard a
>      guess
>      you're doing something like:
>      main = do
>      �  �  contents <- readFile "file.txt"
>      �  �  words contents
>      At the GHCi prompt, each line can be any expression, and GHCi will
>      evaluate it and then display it. The two lines in your session
>      aren't
>      really related.
>      In contrast, the do block in the source file expects the expression
>      at
>      the end to be an IO action.
>      What do you want your program to do when you get to "words
>      contents"?
>      display it? (If you want to display it, pass it to `print`).
>      Quoting Yugesh Kothari (2019-03-26 23:35:14)
>      >�  �  Hi,�
>      >�  �  I am trying to read data from a file.
>      >�  �  When I do-
>      >�  �  ghci> contents <- readFile "file.txt"
>      >�  �  ghci> words contents
>      >�  �  Then everything works.
>      >�  �  The same thing when done in a .hs file gives an IO String vs
>      [String]
>      >�  �  error.
>      >�  �  Why is that so?
>
> Verweise
>
>    1. mailto:kothariyugesh at gmail.com
>    2. mailto:beginners at haskell.org
>    3. mailto:ian at zenhack.net

From noelkwan1998 at gmail.com  Sun Mar 31 12:55:04 2019
From: noelkwan1998 at gmail.com (Noel Kwan)
Date: Sun, 31 Mar 2019 20:55:04 +0800
Subject: [Haskell-beginners] Integrating external dependencies with stack
Message-ID: <CABXP3M5-C8NO6KvouP4a42RtTfhoWVUMiC5OTWA=sYonN5VO0g@mail.gmail.com>

I am trying to use stack to build a web scraper with scalpel. However, it
requires curl-1.8.0 as a dependency and I have no clue how to integrate
this dependency. Any insight would be greatly appreciated.
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