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     dlist-0.8.0.5
Starting     colour-2.3.4
Starting     file-embed-0.0.11
Starting     base-compat-0.10.5
Building     dlist-0.8.0.5
Building     colour-2.3.4
Building     file-embed-0.0.11
Building     base-compat-0.10.5
Completed    dlist-0.8.0.5
Starting     hashable-1.2.7.0
Completed    file-embed-0.0.11
Starting     haskell-src-exts-1.20.3
Building     hashable-1.2.7.0
Failed to install haskell-src-exts-1.20.3
Build log ( /home/builder/.cabal/logs/ghc-8.6.3/haskell-src-exts-1.20.3-2fryh11Yuz7lCtLeeIQn8.log ):
cabal: Entering directory '/tmp/cabal-tmp-18113/haskell-src-exts-1.20.3'
Configuring haskell-src-exts-1.20.3...
cabal: The program 'happy' version >=1.19 is required but it could not be
found.

cabal: Leaving directory '/tmp/cabal-tmp-18113/haskell-src-exts-1.20.3'
Starting     integer-logarithms-1.0.2.2
Building     integer-logarithms-1.0.2.2
Completed    base-compat-0.10.5
Completed    integer-logarithms-1.0.2.2
Completed    hashable-1.2.7.0
Completed    colour-2.3.4
cabal: Error: some packages failed to install:
haskell-src-exts-1.20.3-2fryh11Yuz7lCtLeeIQn8 failed during the configure
step. The exception was:
ExitFailure 1
stylish-haskell-0.9.2.1-J7DqAjEbzi8AtitvZdomW4 depends on
stylish-haskell-0.9.2.1 which failed to install.