The output of
stack ghc -- --version
is
The Glorious Glasgow Haskell Compilation System, version 7.10.3
I want to upgrade to GHC 8.
How can I tell Stack to upgrade GHC?
mac10688
User dysfun from the IRC answered my question so I will post it here for posterity.
To update GHC that's used to compile a project, go to the project's stack.yaml file.
In there is the resolver field. Update that accordingly. Some examples:
resolver: ghc-8.0.2
resolver: lts-9.0
resolver: nightly-2015-09-21
For my case, I learned from this webpage that resolver lts-9.0 uses GHC 8.0.2.
Here's more on Stack's resolvers.
来源：https://stackoverflow.com/questions/45498425/how-to-upgrade-ghc-with-stack