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     Only-0.1
Starting     bytestring-builder-0.10.8.2.0
Starting     base-compat-0.10.5
Building     Only-0.1
Building     bytestring-builder-0.10.8.2.0
Building     dlist-0.8.0.5
Building     base-compat-0.10.5
Completed    bytestring-builder-0.10.8.2.0
Starting     hashable-1.2.7.0
Building     hashable-1.2.7.0
Completed    Only-0.1
Starting     haskell-src-exts-1.20.3
Completed    dlist-0.8.0.5
Starting     integer-logarithms-1.0.2.2
Building     haskell-src-exts-1.20.3
Building     integer-logarithms-1.0.2.2
Completed    hashable-1.2.7.0
Starting     postgresql-libpq-0.9.4.2
Completed    integer-logarithms-1.0.2.2
Starting     primitive-0.6.4.0
Building     primitive-0.6.4.0
Completed    base-compat-0.10.5
Starting     random-1.1
Building     random-1.1
Failed to install postgresql-libpq-0.9.4.2
Build log ( /home/builder/.cabal/logs/ghc-8.6.3/postgresql-libpq-0.9.4.2-HyacS45qPUc33pszxfYdpM.log ):
cabal: Entering directory '/tmp/cabal-tmp-6752/postgresql-libpq-0.9.4.2'
[1 of 1] Compiling Main             ( /tmp/cabal-tmp-6752/postgresql-libpq-0.9.4.2/dist/setup/setup.hs, /tmp/cabal-tmp-6752/postgresql-libpq-0.9.4.2/dist/setup/Main.o )
Linking /tmp/cabal-tmp-6752/postgresql-libpq-0.9.4.2/dist/setup/setup ...
Configuring postgresql-libpq-0.9.4.2...
setup: The program 'pg_config' is required but it could not be found.

cabal: Leaving directory '/tmp/cabal-tmp-6752/postgresql-libpq-0.9.4.2'
Starting     safe-0.3.17
Building     safe-0.3.17
Completed    random-1.1
Completed    safe-0.3.17
Completed    primitive-0.6.4.0
Completed    haskell-src-exts-1.20.3
cabal: Error: some packages failed to install:
postgresql-libpq-0.9.4.2-HyacS45qPUc33pszxfYdpM failed during the configure
step. The exception was:
ExitFailure 1
postgresql-simple-0.6-AUYYqF1Ip9i6KjeltQZU0G depends on postgresql-simple-0.6
which failed to install.
postgresql-simple-typed-0.1.1.1-5SUg2Yr70458x3qKqfx0Lv depends on
postgresql-simple-typed-0.1.1.1 which failed to install.