Cabal errors

cabal

✗ cabal v2-build
Warning: The package list for 'hackage.haskell.org' does not exist. Run 'cabal
update' to download it.
Resolving dependencies...
cabal: Could not resolve dependencies:
[__0] next goal: ptghci (user goal)
[__0] rejecting: ptghci-0.1.0.0 (conflict: pkg-config package python3-any, not
found in the pkg-config database)
[__0] fail (backjumping, conflict set: ptghci)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: ptghci


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

Please switch to using either the new project style and the new-update command
or the legacy v1-update 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

Downloading the latest package list from hackage.haskell.org

✗ pkg-config --cflags --libs python3
Package python3 was not found in the pkg-config search path.
Perhaps you should add the directory containing `python3.pc'
to the PKG_CONFIG_PATH environment variable
No package 'python3' found

✗ which python3
/opt/local/bin/python3

✗ echo $PKG_CONFIG_PATH
/opt/local/bin/python3

✗ echo $PKG_CONFIG_PATH
/opt/local/bin

✗ pkg-config --cflags --libs python3
Package python3 was not found in the pkg-config search path.
Perhaps you should add the directory containing `python3.pc'
to the PKG_CONFIG_PATH environment variable
No package 'python3' found

✗ locate python3.pc
/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/pkgconfig/python3.pc
/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/pkgconfig/python3.pc
/usr/local/Cellar/python/3.6.5/lib/pkgconfig/python3.pc
/usr/local/lib/pkgconfig/python3.pc
➜ ptghci git:(master) ✗ PKG_CONFIG_PATH=/usr/local/lib/pkgconfig
➜ ptghci git:(master) ✗ pkg-config --cflags --libs python3
Package python3 was not found in the pkg-config search path.
Perhaps you should add the directory containing `python3.pc'
to the PKG_CONFIG_PATH environment variable
No package 'python3' found

✗ PKG_CONFIG_PATH=/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/pkgconfig
➜ ptghci git:(master) ✗ pkg-config --cflags --libs python3
Package python3 was not found in the pkg-config search path.
Perhaps you should add the directory containing `python3.pc'
to the PKG_CONFIG_PATH environment variable
No package 'python3' found