Stackage is a repository for Haskell packages. We can add these packages to a stack project.
In a stack project, there is a file called
stack.yaml there is a segment that looks like:
Stackage keeps a list of packages for every revision of
lts. In our case we want the list of packages for
lts-6.8 To find these packages visit:
https://www.stackage.org/lts-6.8 # if a different version is used, change 6.8 to the correct resolver number.
Looking through the packages, there is a Lens-4.13.
We can now add the language package by modifying the section of
build-depends: base >= 4.7 && < 5
build-depends: base >= 4.7 && 5, lens == 4.13
Obviously, if we want to change a newer LTS (after it's released), we just change the resolver number, eg.:
With the next
stack build Stack will use the LTS 6.9 version and hence download some new dependencies.