Aha!  That works.  I would never in a million years have found that by myself.  
Thank you.

But

  *   It is terribly mysterious that “cabal install hspec” doesn’t, well, 
install hspec.
  *   It must surely be a bug that “cabal install –lib hspec” simply crashes.

Simon

From: Brandon Allbery <allber...@gmail.com>
Sent: 15 April 2019 23:03
To: Simon Peyton Jones <simo...@microsoft.com>
Cc: ghc-devs@haskell.org
Subject: Re: Cabal woes

Yes, I think a lot of documentation will need to be updated because this. You 
want "cabal v1-install" with cabal 3.

On Mon, Apr 15, 2019 at 6:00 PM Simon Peyton Jones 
<simo...@microsoft.com<mailto:simo...@microsoft.com>> wrote:
Thanks.  But alas I have no clue about whether I want a v1-install or a 
v2-install, nor how to achieve them if I knew what they were.  I just want to 
install ‘hspec’ so that I can use it when compiling a program.  How would I do 
that?

The instructions here 
https://wiki.haskell.org/Cabal-Install<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki.haskell.org%2FCabal-Install&data=02%7C01%7Csimonpj%40microsoft.com%7C9dba03cd18af405d806208d6c1ee1601%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636909625657350786&sdata=81SaQYxWkpF9nYalL%2B%2FSCbcGMMkYsMnFnpylDncDXu0%3D&reserved=0>
 just say “cabal install hspec” which is what I tried.  Those instructions are 
pointed to from here 
https://wiki.haskell.org/Cabal/How_to_install_a_Cabal_package<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki.haskell.org%2FCabal%2FHow_to_install_a_Cabal_package&data=02%7C01%7Csimonpj%40microsoft.com%7C9dba03cd18af405d806208d6c1ee1601%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636909625657350786&sdata=ougOkZ0Dd%2Fep%2FshvVChLiGb9MEhEOW1sYxGnK8KJ8ww%3D&reserved=0>,
 which in turn are pointed to from the main Cabal home page 
https://www.haskell.org/cabal/<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.haskell.org%2Fcabal%2F&data=02%7C01%7Csimonpj%40microsoft.com%7C9dba03cd18af405d806208d6c1ee1601%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636909625657360794&sdata=I1SnV%2F4c2d05K39NLK%2FQ%2BLdfRoGRRCcKIGXHkNKMGH8%3D&reserved=0>.

I must be missing something.

Simon

From: Brandon Allbery <allber...@gmail.com<mailto:allber...@gmail.com>>
Sent: 15 April 2019 22:54
To: Simon Peyton Jones <simo...@microsoft.com<mailto:simo...@microsoft.com>>
Cc: ghc-devs@haskell.org<mailto:ghc-devs@haskell.org>
Subject: Re: Cabal woes

I think you wanted v1-install to install a library into the user package 
database, since your cabal is 3.x and the v2-* commands are now the default 
(that is, you did what used to be cabal new-install or cabal v2-install).

On Mon, Apr 15, 2019 at 5:47 PM Simon Peyton Jones via ghc-devs 
<ghc-devs@haskell.org<mailto:ghc-devs@haskell.org>> wrote:
I’m trying to install ‘hspec’ on my WSL (Windows subsystem for Linux) system.
But I fail; see below.
For some reason cabal complains about installing a library.  (That seems 
peculiar – isn’t that what cabal is for?)  But it helpfully suggests adding 
–lib.
Alas, cabal then crashes outright, which should never happen.
So I’m stuck.  What should I do?
Thanks
Simon


simonpj@MSRC-9870733:~$ cabal --version

cabal-install version 3.0.0.0

compiled using version 3.0.0.0 of the Cabal library

simonpj@MSRC-9870733:~$ cabal install hspec

Resolving dependencies...

Up to date

Warning: You asked to install executables, but there are no executables in

target: hspec. Perhaps you want to use --lib to install libraries instead.

simonpj@MSRC-9870733:~$ cabal install --lib hspec

Resolving dependencies...

Up to date

Distribution/Simple/GHC.hs:1959:5-56: Irrefutable pattern failed for pattern 
Just ghcPkgProg



simonpj@MSRC-9870733:~$ which ghc

/opt/ghc/bin/ghc

simonpj@MSRC-9870733:~$ which ghc-pkg

/opt/ghc/bin/ghc-pkg

simonpj@MSRC-9870733:~$


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allber...@gmail.com<mailto:allber...@gmail.com>


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allber...@gmail.com<mailto:allber...@gmail.com>
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