Multiple versions of happy

What's the approved mechanism to install multiple versions of happy/alex etc? Eg I tried to build ghc-9.0 and got this: checking for makeinfo... no checking for python3... /usr/bin/python3 checking for ghc-pkg matching /opt/ghc/bin/ghc... /opt/ghc/bin/ghc-pkg checking for happy... /home/simonpj/.cabal/bin/happy checking for version of happy... 1.20.0 configure: error: Happy version 1.19 is required to compile GHC. I so I have to 1. Install happy-1.19 without overwriting the installed happy-1.20 2. Tell configure to use happy-1.19 What's the best way to do those two things? Thanks Simon