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...
Downloading  shellmet-0.0.1
Downloaded   shellmet-0.0.1
Starting     shellmet-0.0.1
Building     shellmet-0.0.1
Failed to install shellmet-0.0.1
Build log ( /home/builder/.cabal/logs/ghc-8.6.3/shellmet-0.0.1-EWpLHDmi6gpGZubC3ggCpA.log ):
cabal: Entering directory '/tmp/cabal-tmp-3238/shellmet-0.0.1'
Configuring shellmet-0.0.1...
Preprocessing library for shellmet-0.0.1..
Building library for shellmet-0.0.1..
[1 of 1] Compiling Shellmet
Preprocessing executable 'readme' for shellmet-0.0.1..
Building executable 'readme' for shellmet-0.0.1..
ghc: could not execute: markdown-unlit
cabal: Leaving directory '/tmp/cabal-tmp-3238/shellmet-0.0.1'
cabal: Error: some packages failed to install:
shellmet-0.0.1-EWpLHDmi6gpGZubC3ggCpA failed during the building phase. The
exception was:
ExitFailure 1