How to upgrade GHC with Stack

Question

The output of

stack ghc -- --version

is

The Glorious Glasgow Haskell Compilation Syste         


        

Answer 1

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.