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I am trying to understand how to use stack and stackage.org. When I first installed it and used it, stackage.org was at LTS-3.8 (the "resolver"). Since then, stackage.org now has LTS-3.11.
First, I'd like to confirm what this means. Stackage is a repository of packages in which, for a specific LTS version (say 3.8), the packages have been verified to work together. So the packages of LTS-3.8 work together, and the packages of LTS-3.11 also work together. Moving on ...
When I run stack new projectname, stack tells me:
Checking against build plan lts-3.8 Selected resolver: lts-3.8 Does this mean that the project has been set up to use only the packages and versions that were verified under LTS-3.8?
If I now want to start a new project and want to use the latest LTS version with the new project, how do I tell stack to do that by default?
What about if I want to "upgrade" an older project to use a new LTS version?
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stack ghci allows you to load components and files of your project into ghci . It uses the same TARGET syntax as stack build , and can also take options like --test , --bench , and --flag . Similarly to stack build , the default is to load up ghci with all libraries and executables in the project.
html -> click on system information-> login with admin rights -> you can get all details about the installed server.
To build your project, Stack uses a project-level configuration file, named stack. yaml , in the root directory of your project as a sort of blueprint. That file contains a reference, called a resolver, to the snapshot which your package will be built against.
In its default configuration, Stack will simply ignore any system GHC installation and use a sandboxed GHC that it has installed itself. You can find these sandboxed GHC installations in the ghc-* directories in the stack path --programs directory.
Does this mean that the project has been set up to use only the packages and versions that were verified under LTS-3.8?
Exactly. (And if you ever need packages not included in the LTS 3.8 set you can specify them through the extra-deps section of stack.yaml. stack will grab them from Hackage and install them separately for your project, without affecting the LTS snapshot or your other projects.)
If I now want to start a new project and want to use the latest LTS version with the new project, how do I tell stack to do that by default?
Use e.g. stack new projectname --resolver=lts-3.11 to set the resolver for a new project. stack defaults to the most recent LTS snapshot you are already using, and so once you have a project with the latest LTS future new projects will follow suit.
What about if I want to "upgrade" an older project to use a new LTS version?
Change the resolver field in the stack.yaml file. The change will take effect the next time you build the project.
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