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  text-utf8-1.2.3.0
Starting     util-0.1.13.0
Starting     base-unicode-symbols-0.2.3
Building     util-0.1.13.0
Building     base-unicode-symbols-0.2.3
Downloaded   text-utf8-1.2.3.0
Starting     text-utf8-1.2.3.0
Building     text-utf8-1.2.3.0
Completed    base-unicode-symbols-0.2.3
Completed    util-0.1.13.0
Completed    text-utf8-1.2.3.0
Downloading  lean-0.0.0.1
Downloaded   lean-0.0.0.1
Starting     lean-0.0.0.1
Building     lean-0.0.0.1
Failed to install lean-0.0.0.1
Build log ( /home/builder/.cabal/logs/ghc-8.6.3/lean-0.0.0.1-KwQQ8ypcBjHLvOrK3NzIRG.log ):
cabal: Entering directory '/tmp/cabal-tmp-23349/lean-0.0.0.1'
Configuring lean-0.0.0.1...
Preprocessing library for lean-0.0.0.1..
Decl.hsc:13:10: fatal error: lean.h: No such file or directory
compilation terminated.
compiling dist/build/Lean/Raw/C/Decl_hsc_make.c failed (exit code 1)
command was: /usr/bin/gcc -c dist/build/Lean/Raw/C/Decl_hsc_make.c -o dist/build/Lean/Raw/C/Decl_hsc_make.o -fno-stack-protector -fno-stack-protector -fuse-ld=gold -D__GLASGOW_HASKELL__=806 -Dlinux_BUILD_OS=1 -Dx86_64_BUILD_ARCH=1 -Dlinux_HOST_OS=1 -Dx86_64_HOST_ARCH=1 -Idist/build/autogen -Idist/build/global-autogen -include dist/build/autogen/cabal_macros.h -I/opt/ghc/8.6.3/lib/ghc-8.6.3/bytestring-0.10.8.2/include -I/opt/ghc/8.6.3/lib/ghc-8.6.3/base-4.12.0.0/include -I/opt/ghc/8.6.3/lib/ghc-8.6.3/integer-gmp-1.0.2.0/include -I/opt/ghc/8.6.3/lib/ghc-8.6.3/include -I/opt/ghc/8.6.3/lib/ghc-8.6.3/include/
cabal: Leaving directory '/tmp/cabal-tmp-23349/lean-0.0.0.1'
cabal: Error: some packages failed to install:
lean-0.0.0.1-KwQQ8ypcBjHLvOrK3NzIRG failed during the building phase. The
exception was:
ExitFailure 1