I installed stack on my Windows computer using chocolatey, which went smoothly. But I had nothing anywhere I could find. On a hunch, at the prompt I tried to run stack ghci, then it started downloading and installing stuff. Good. I then was able to track down an example of a stack.yaml in the ...stack/global-project directory. My whole motivation was to see an actual global stack.yaml in the wild, and not have to guess-and-test from the stack docs. Good. I duplicated

packages: []

resolver: lts-17.15

on my Ubuntu 21.04 in the .stack/global-project/stack.yaml. Tried running stack ghci from the Ubuntu prompt, and, similarly, it started installing lots of stuff. (The resolver version I replaced was lts-17.08. Why that old I don't know.). But then I got a cryptic error as it seemed to clash or not like something it saw in some obscure github directory I had cloned ages ago with Haskell example code. I deleted everything in the github directory that looked stack/cabal-ish and tried stack ghci again. Now it says

Warning (added by new or init): Some packages were found to have names conflicting with others and have been commented out in the packages section.
Warning (added by new or init): Some packages were found to be incompatible with the resolver and have been left commented out in the packages section.
You can omit this message by removing it from stack.yaml

Stack looks for packages in the directories configured in
the 'packages' and 'extra-deps' fields defined in your stack.yaml
The current entry points to /home/galaxybeing/Dropbox/org/HaskellRoad/,
but no .cabal or package.yaml file could be found there.

Yes, that was the directory I purged. My .stack/global-project/stack.yaml contains only

packages: []
resolver: lts-17.15

Not sure how to proceed. Seeing how that vast majority of Haskell intro books don't use projects, just install, start ghci, load code at the REPL prompt, I'd really like to nail this "global", non-project stack down.

On Sun, Jun 6, 2021 at 7:10 PM Travis Cardwell <travis.cardwell@extrema.is> wrote:

The Stack configuration that is used outside of projects is stored in
the following location:

~/.stack/global-project/stack.yaml

This configuration file is used when you run `stack ghci` outside of a
project. Such project configuration files can specify the Stackage
snapshot to be used (`resolver`), any packages that should be used that
are different from or not in the specified Stackage snapshot
(`extra-deps`), a list of packages that are being developed (`packages`,
none by default in the "global project"), as well as some other settings
documented at the following location.

https://docs.haskellstack.org/en/stable/yaml_configuration/

Such a project configuration file determines what packages are
*available* for use. The motivation is to provide an environment where
all of the available packages work together, saving you from having to
deal with dependency conflicts. It does not *expose* packages to the
compiler or REPL. Packages are usually exposed by specifying them in a
`.cabal` file (or `package.yaml` file when using hpack).

In my experience, the `~/.stack/global-project/stack.yaml` configuration
is most often used when installing executables using Stack. For example,
one can install the version of `hlint` that is in the Stackage snapshot
configured in the configuration file as follows:

stack install hlint

What you would like to do is not normal usage of Stack, but I understand
your motivation. It is possible to do what you want by configuring a
global project with the packages that you would like to make available.
First, create file `~/.stack/global-project/global-project.cabal` with
the following content:

name: global-project
version: 0.0.0.0
cabal-version: 1.24
build-type: Simple

library
build-depends:
base
, safe
default-language: Haskell2010

Add any packages that you would like to expose to the `build-depends`
list. Next, configure `~/.stack/global-project/stack.yaml` as follows:

resolver: lts-17.14

packages:
- .

Update the `resolver` configuration whenever you want to change Stackage
snapshots. Note that you will need to add `extra-deps` configuration to
this file if you ever want to expose a package that is not in the
configured snapshot, in addition to adding it to the `build-depends`
list.

With this configuration, the listed packages should be exposed when you
run `stack ghci` to run a REPL.

Good luck!

Travis