CODEWITHSUNDEEP
haskellcabalnix
Gspia
Gspia

Reputation: 809

How to make cabal to be found in a straigthforward nix-pill 8.1 imitation?

The cabal isn't found on the following example and the question is, how to correct the example so that cabal is found.

This example is very straigthforward modification of the nix pill 8.1. On nix-repl, typing :l <nixpkgs> and then "${cabal-install}" gives a path to the store where cabal-install is and it contains sub-dirs with bin there containing cabal-executable. I.e.

> /nix/store/pathtocabal-install/bin/cabal -v
cabal-install version 2.0.0.0
compiled using version 2.0.0.2 of the Cabal library

Below you should find the files corresponding to the the "make c" example.

With them, the

> nix-build hello.nix

doesn't work. It first tells to build "these derivations" and then says that 

hello_builder.sh: line 2: cabal: command not found

I'm suspecting that $cabal-install/bin is a wrong way to refer to cabal but on nix-repl its store-path is found.

hello_builder.sh is even shorter than in the c-example. Note that installation part is still missing (first the builder should be made to find the cabal).

export PATH="$coreutils/bin:$ghc/bin:$cabal-install/bin:$binutils/bin"
cabal build hello

hello.nix - maybe the binutils is not needed. 

with (import <nixpkgs> {});
derivation {
  name = "hello";
  builder = "${bash}/bin/bash";
  args = [ ./hello_builder.sh ];
  inherit binutils coreutils ghc cabal-install;
  src = ./hello.cabal;
  system = builtins.currentSystem;
}

hello.cabal - in nix-shell with cabal-install and ghc, this works.

name:                hello
version:             0.1.0.0
build-type:          Simple
cabal-version:       >=1.24

executable hello
  main-is:             hello.hs
  default-language:    Haskell2010
  build-depends:       base              >=4.9 && <4.10

hello.hs

module Main where

main :: IO ()
main = putStrLn "Hello there!"

Late additions:

By adding echo $PATH to the builder, we can see that the path is not correct. It is /nix/store/...coreutils-8.28/bin:/nix/store...ghc-8.0.2/bin:-install/bin:/nix/store/...binutils-2.28.1/bin. There the $cabal is turned into an empty string and it is not referring to $cabal-install. Thus there is no correct store-path for the cabal-executable.

This answers part of the why-part of the question and how to correct it remains. And the open why-part is, why inherit cabal-install cannot be used here.

Upvotes: 0

Views: 83

Answers (1)

Emmanuel Rosa
Emmanuel Rosa

Reputation: 9885

The problem with inherit cabal-install; is that cabal-install is not a valid variable name in BASH. Nix converts the keys in the set provided to derivation into variables in BASH.

Instead of inherit cabal-install; you can do something like cabal_install = cabal-install; and then use cabal_install in your builder.

Upvotes: 1

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