Warning: The install command is a part of the legacy v1 style of cabal usage.

Please switch to using either the new project style and the new-install
command or the legacy v1-install alias as new-style projects will become the
default in the next version of cabal-install. Please file a bug if you cannot
replicate a working v1- use case with the new-style commands.

For more information, see: https://wiki.haskell.org/Cabal/NewBuild

Resolving dependencies...
Starting     call-stack-0.1.0
Starting     hashable-1.2.7.0
Building     hashable-1.2.7.0
Building     call-stack-0.1.0
Completed    call-stack-0.1.0
Starting     mtl-compat-0.2.1.3
Building     mtl-compat-0.2.1.3
Completed    mtl-compat-0.2.1.3
Starting     network-2.8.0.0
Completed    hashable-1.2.7.0
Starting     old-locale-1.0.0.7
Building     old-locale-1.0.0.7
Completed    old-locale-1.0.0.7
Starting     random-1.1
Building     network-2.8.0.0
Building     random-1.1
Completed    random-1.1
Starting     regex-base-0.93.2
Building     regex-base-0.93.2
Completed    regex-base-0.93.2
Starting     transformers-compat-0.6.2
Building     transformers-compat-0.6.2
Completed    network-2.8.0.0
Starting     HUnit-1.6.0.0
Building     HUnit-1.6.0.0
Completed    transformers-compat-0.6.2
Starting     async-2.2.1
Building     async-2.2.1
Completed    HUnit-1.6.0.0
Starting     old-time-1.1.0.3
Building     old-time-1.1.0.3
Completed    async-2.2.1
Starting     regex-posix-0.95.2
Building     regex-posix-0.95.2
Completed    old-time-1.1.0.3
Starting     hslogger-1.2.12
Building     hslogger-1.2.12
Completed    regex-posix-0.95.2
Starting     protolude-0.2.3
Building     protolude-0.2.3
Completed    hslogger-1.2.12
Starting     regex-compat-0.95.1
Building     regex-compat-0.95.1
Completed    regex-compat-0.95.1
Starting     MissingH-1.4.1.0
Building     MissingH-1.4.1.0
Completed    protolude-0.2.3
Completed    MissingH-1.4.1.0
Starting     language-elm-0.1.1.2
Failed to install language-elm-0.1.1.2
Build log ( /home/builder/.cabal/logs/ghc-8.6.1/language-elm-0.1.1.2-DcnpE9Ilxbg2GA2YIP3JzE.log ):
cabal: Entering directory '/tmp/cabal-tmp-24830/language-elm-0.1.1.2'
Configuring language-elm-0.1.1.2...
cabal: The program 'doctest' is required but it could not be found.

cabal: Leaving directory '/tmp/cabal-tmp-24830/language-elm-0.1.1.2'
cabal: Error: some packages failed to install:
language-elm-0.1.1.2-DcnpE9Ilxbg2GA2YIP3JzE failed during the configure step.
The exception was:
ExitFailure 1