Multiple versions of happy

Simon Peyton Jones simonpj at
Tue Mar 30 13:22:04 UTC 2021

That's (2), thanks.  How about (1)?

From: Sebastian Graf <sgraf1337 at>
Sent: 30 March 2021 14:22
To: Simon Peyton Jones <simonpj at>
Cc: ghc-devs at
Subject: Re: Multiple versions of happy

Hi Simon,

According to the configure script, you can use the HAPPY env variable. e.g.

$ HAPPY=/full/path/to/happy ./configure

Hope that helps. Cheers,

Am Di., 30. März 2021 um 15:19 Uhr schrieb Simon Peyton Jones via ghc-devs <ghc-devs at<mailto:ghc-devs at>>:
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?
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