{ runCommand, haskellPackages, fetchurl }:

let paths = p: with p; [ shake shake-language-c aeson yaml ];
    ghc = haskellPackages.ghcWithPackages paths;
    src = fetchurl { url = "http://.../Foo.hs"; ... };
in runCommand "Foo" { buildInputs = [ ghc ]; } ''
    mkdir -pv $out/bin
    cp -vi ${src} Foo.hs
    ghc -O2 Foo.hs -o $out/bin/Foo
''