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Today's Topics:
1. Re: Question on terminology (Ben Rogalski)
2. Re: Question on terminology (Rein Henrichs)
3. failing to install GHC 7.10.3 appears to have broken cabal
and stack (Jeffrey Brown)
----------------------------------------------------------------------
Message: 1
Date: Thu, 3 Mar 2016 13:10:39 -0500
From: Ben Rogalski <bwrogal...@gmail.com>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] Question on terminology
Message-ID:
<cal-j+nkjq9at7hmulj00seuxyg3ehk86+hnhteu14+j+v18...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I'm having trouble understanding this:
> IIUC, one would describe fmap as "lifting" a function g into a functor f,
> in the sense of
>
> Functor f => (g a b) -> g a -> g b
>
>
> Is there an inverse concept (? co-lift ?) that describes
>
> Functor f => (g a -> g b) -> a -> b
>
It seems like these are type declarations for functions, with class
constraints that say f must be a Functor, but then f doesn't appear
anywhere else in the declaration. Why is this?
Thanks,
-Ben
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Message: 2
Date: Thu, 03 Mar 2016 19:13:25 +0000
From: Rein Henrichs <rein.henri...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Question on terminology
Message-ID:
<cajp6g8x6q2eddpr-qefhdrvs3va8dyp0iv8ba+ps5zw+fcx...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Ben, I just assumed that g was a typo for f.
On Thu, Mar 3, 2016 at 10:10 AM Ben Rogalski <bwrogal...@gmail.com> wrote:
> I'm having trouble understanding this:
>
> > IIUC, one would describe fmap as "lifting" a function g into a functor f,
> > in the sense of
> >
> > Functor f => (g a b) -> g a -> g b
> >
> >
> > Is there an inverse concept (? co-lift ?) that describes
> >
> > Functor f => (g a -> g b) -> a -> b
> >
>
> It seems like these are type declarations for functions, with class
> constraints that say f must be a Functor, but then f doesn't appear
> anywhere else in the declaration. Why is this?
>
> Thanks,
> -Ben
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 3
Date: Thu, 3 Mar 2016 16:56:25 -0800
From: Jeffrey Brown <jeffbrown....@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: [Haskell-beginners] failing to install GHC 7.10.3 appears to
have broken cabal and stack
Message-ID:
<caec4ma3zo2xbkgtvvpcfe54tongag_7rhbn7qmw4ls4s46g...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I use Ubuntu 14.04.
Outside of a stack context, I have been using GHC 7.8.4. I tried to install
7.10.3. ./configure worked, but make install failed with this error:
make[1]: *** No rule to make target
`utils/haddock/dist/build/tmp/haddock', needed by `install_libexecs'. Stop.
make: *** [install] Error 2
I tried to manually undo the install, by deleting it from /usr/local/lib,
and by changing all the symlinks in /usr/local/bin back to 7.8.4.
If I run ghci without stack, it works, and is still at version 7.8.4. But
now cabal and stack are producing errors.
"cabal update" runs, but "cabal install" gets confused:
jeff@jeffLenovUbu:~/dwt_git_hask$ cabal install regex-compat
Warning: cannot determine version of /usr/local/bin/hpc :
""
Warning: cannot determine version of /usr/local/bin/hsc2hs :
""
Resolving dependencies...
Configuring regex-posix-0.95.2...
Building regex-posix-0.95.2...
Preprocessing library regex-posix-0.95.2...
/usr/local/bin/hsc2hs: line 29: /usr/local/lib/ghc-7.10.3/bin/hsc2hs:
No such file or directory
Failed to install regex-posix-0.95.2
cabal: Error: some packages failed to install:
regex-compat-0.95.1 depends on regex-posix-0.95.2 which failed to
install.
regex-posix-0.95.2 failed during the building phase. The exception was:
ExitFailure 127
jeff@jeffLenovUbu:~/dwt_git_hask$
As an example of a stack problem, I downloaded Oleg Prophet's
implementation of MicroKanren [1]. "stack build" ran without complaint (or
visible output), but "stack ghci" fails thus:
jeff@jeffLenovUbu:~/work/computer/Haskell/microKanren/featherweight$
stack ghciConfiguring GHCi with the following packages: microKanren
GHCi, version 7.10.2: http://www.haskell.org/ghc/ :? for help
<command line>: cannot satisfy -package QuickCheck
(use -v for more information)
jeff@jeffLenovUbu:~/dwt_git_hask$
stack ghci even fails (with a different error) on my own project [2]:
jeff@jeffLenovUbu:~/dwt_git_hask$ stack ghci
Configuring GHCi with the following packages: Dwt
GHCi, version 7.10.2: http://www.haskell.org/ghc/ :? for help
<command line>: can't load .so/.DLL for:
/home/jeff/dwt_git_hask/.stack-work/install/x86_64-linux/nightly-2015-08-03/7.10.2/lib/x86_64-linux-ghc-7.10.2/Dwt-0.1.0.0-7VW1kKp7le6K6OdeGoRsDt/
libHSDwt-0.1.0.0-7VW1kKp7le6K6OdeGoRsDt-ghc7.10.2.so
(/home/jeff/dwt_git_hask/.stack-work/install/x86_64-linux/nightly-2015-08-03/7.10.2/lib/x86_64-linux-ghc-7.10.2/Dwt-0.1.0.0-7VW1kKp7le6K6OdeGoRsDt/
libHSDwt-0.1.0.0-7VW1kKp7le6K6OdeGoRsDt-ghc7.10.2.so: undefined symbol:
Dwtzu7VW1kKp7le6K6OdeGoRsDt_DwtziSearch_QNode_con_info)
jeff@jeffLenovUbu:~/dwt_git_hask$
Thanks in advance for your help.
[1] https://github.com/Oregu/featherweight
[2] https://github.com/JeffreyBenjaminBrown/digraphs-with-text
--
Jeffrey Benjamin Brown
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