Ensure that cabal --version is >= 3.
In an empty folder, type
cabal install --lib --package-env . random
That should create a file named .ghc.environment.<somemorestuff> in the folder.
In that same empty folder, start ghci:
ghci
Some message like “Loaded package environment from…” should appear when starting.
Inside ghci, import System.Random.
Prelude> import System.Random
If, when installing the package, you omit the location of the package environment:
cabal install --lib random
then it updates a default package environment located somewhere in your home directory.
With a bit of luck, ghci invocations should pick this default environment, too, but explicitly writing –package-env . is more foolprof.
Some relevant links: