I've followed the steps here; however, it doesn't replace or supercede an older version of ghci from my Ubuntu 18.04:
12:47:02:~$ which ghci
/opt/ghc/8.0.2/bin/ghci
12:47:14:~$ ghci --version
The Glorious Glasgow Haskell Compilation System, version 8.0.2
I've tried various removes, but to no avail. The newer version is on my system:
12:50:32:/usr/local/haskell/ghc-8.4.2-x86_64/bin$ ./ghci --version
The Glorious Glasgow Haskell Compilation System, version 8.4.2
But I don't know what to do about this old "default" version.
LB