Find the package a Haskell module belongs to

Question

I'm new to Haskell stack and wondering how to find out the name of the package that contains a particular module.

Currently, I want to use Data.Tuple.Extra(fst3) ( https://hackage.haskell.org/package/extra-1.7.9/docs/Data-Tuple-Extra.html ) and want to know what I should write below

    $ stack install ????

I've already installed the tuple package, which, however, doesn't seem to include the Extra part.

All the Internet resources about the installation of a package I've found so far say something along the lines of "To use Blahblah.Anything.Something, you need to install the foofoo package" . . . How can one know? I searched Stackage but it shows only the documentation of Data.Tuple.Extra and I still fail to find the name of the package.

Edit: As K.A.Buhr notes in her/his answer, stack install is the wrong command for the above case. Use stack build instead.

Answer 1

When browsing package documentation in Hackage, the top-left portion of the page header will always give the package, version number, and description. On the page you link, it's here:

You can also use the "Contents" link in the top-right to go to the main page for the extra package, which gives its full list of modules, licensing, links to the package home page and bug tracker, and so on.

As a side note, stack install extra is technically the wrong command to "install" this package. If you want to make the extra package available for use within the Stack global project, the correct command is stack build extra. If you want to use extra within a stack project, then you want to add extra to the dependencies in your package's xxx.cabal or package.yaml file instead and run stack build (no arguments) to build and install it for use in your project.

In contrast, the stack install command is equivalent to stack build --copy-bins which copies any executables in the package to ~/.local/bin so they'll be in your path. See the Stack docs. It's intended to be used for installing programs written in Haskell that are distributed via Stack, so you can do stack install hlint to install the hlint linter, for example.

In this case, because the extra package has no executables, stack install extra and stack build extra will do the same thing, but it's better to get into the habit of using stack build when you aren't intending to install any package binaries, to avoid surprises.