[list-ops] Make foldl' call unambiguous.

[IsaacG]

/solution/test/Tests.hs:80:9: error: [GHC-87543]
    Ambiguous occurrence ‘foldl'’.
    It could refer to
       either ‘Prelude.foldl'’,
              imported from ‘Prelude’ at test/Tests.hs:(8,1)-(16,5)
              (and originally defined in ‘ghc-internal-9.1003.0:GHC.Internal.Data.Foldable’),
           or ‘ListOps.foldl'’,
              imported from ‘ListOps’ at test/Tests.hs:22:7-12.
   |
80 |         foldl' (flip (:)) [] "asdf" `shouldBe` "fdsa"
   |         ^^^^^^

[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

[no important files changed]

For more information, refer to the documentation. If you are unsure whether to add the message or not, please ping @exercism/maintainers-admin in a comment. Thank you!

[MatthijsBlom]

I think a [no important files changed] would be fitting.

---

Prior to base-4.20.0.0 (bundled with GHC 9.10), foldl' was not re-exported by the Prelude. But from base-4.20.0.0 onward it is, hence the error that the proposed change fixes.

All other names defined in ListOps were already exported by the Prelude. This conflict was solved by hiding these while importing the Prelude. Rather than disambiguating all its uses, add foldl' to this import list.

---

The solution stub file should be patched as well.

[IsaacG]

I think a [no important files changed] would be fitting.

I completely agree. That needs to be in the merge message when the track maintainer merges this PR.

The solution stub file should be patched as well.

Done.

Thanks for the explanation and details!

[MatthijsBlom]

Both …/list-ops/.meta/…/ListOps.hs and …/list-ops/test/Tests.hs are good now.

By "the solution stub file" I meant …/list-ops/src/ListOps.hs. That one should receive the same patch as the other two.

---

Hiding a nonexistent export gives rise to merely a GHC-61689 -Wdodgy-imports warning, so it looks like this change is backwards-compatible.

---

...Except apparently the tests have -Werror=dodgy-imports. I guess as a consequence of a -Werror=all or something somewhere.

[IsaacG]

By "the solution stub file" I meant …/list-ops/src/ListOps.hs. That one should receive the same patch as the other two.

Woops. Missed that one. Added now.

[IsaacG]

Eh. This PR was meant in service of the test runner upgrade. If that lands first, a test rerun ought to pass here.

Unrelated, there's a bunch of other PRs in this repo worth a look, too!

[MatthijsBlom]

I think the tests fail because of

haskell/bin/test-example

Line 58 in 9e4f385

--pedantic `# Enable -Wall and -Werror. `\

I guess they could be made to pass again by adding --ghc-options="-Wwarn=dodgy-imports" to that stack call.
But we could also just wait until the track moves on to use base-4.20+ (GHC 9.10+).

[IsaacG]

@tofische With the test runner updated, it might be worth rerunning the failed check here