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54 lines
1.3 KiB
Text
54 lines
1.3 KiB
Text
= Access a Haskell library package in the nixpkgs repo (without using a `.cabal` file)
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////
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$ mkdir tempwork
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$ cd tempwork
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$ cp ../Main.hs ../flake.nix .
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$ git add Main.hs flake.nix
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$ nix develop
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$ git add flake.lock
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$ git commit -a -m temp
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////
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Occasionally you might want to run a short Haskell program that depends on a Haskell library,
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but you don't want to bother writing a cabal file.
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In this example, we will access the `extra` package from the `haskellPackages` set in the nixpkgs repo.
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[NOTE]
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====
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For non-trivial Haskell development projects,
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it's usually more convenient to use `haskell-flake` as described in <<#haskell-flake>>,
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together with the _high-level workflow_ described in <<_development_workflows>>.
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====
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[source,nix,linenums,highlight='11,16']
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.flake.nix
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....
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include::flake.nix[]
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....
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Line 12 makes a custom GHC that knows about `extra`,
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and line 16 makes that custom GHC available in the development environment.
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Here's a short Haskell program that uses the new flake.
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[source,haskell,linenums]
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.Main.hs
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....
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include::Main.hs[]
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....
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Here's a demonstration using the program.
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....
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$ runghc Main.hs # Fails; dependency not available
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$# start-shell nix develop <<EOL
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$ runghc Main.hs # Works in development environment
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$# EOL
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....
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////
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Good adoc0 scripts clean up after themselves.
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$ exit
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$ cd .. ; rm -rf tempwork # clean up
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////
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