travis: Test ghc 8.0.1 (and avoid some compiler warnings on 8.0.1) #120
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
petertseng
changed the title
|
will rebase in next 24 hours. I can and should be prodded if not. by the way 8.0.1 is no longer pre-release, so this becomes much more relevant. |
Note that this only affects the example, not the tests.
GHC 8.0.1 will give the error:
```
BST.hs:15:1: warning: [-Wredundant-constraints]
• Redundant constraint: Ord a
• In the type signature for:
singleton :: Ord a => a -> BST a
```
That makes sense, since you can make any value a singleton tree; it
doesn't necessarily have to be Ord. Of course, you'll find yourself
unable to add other values to the tree if it's not Ord, but that's not
`singleton`'s problem.
Note that this only affects the example, not the tests.
GHC 8.0.1 will give the error:
```
CustomSet.hs:30:10: warning: [-Wredundant-constraints]
• Redundant constraint: Eq a
• In the instance declaration for ‘Eq (CustomSet a)’
CustomSet.hs:50:1: warning: [-Wredundant-constraints]
• Redundant constraint: Ord a
• In the type signature for:
singleton :: Ord a => a -> CustomSet a
CustomSet.hs:56:1: warning: [-Wredundant-constraints]
• Redundant constraint: Ord a
• In the type signature for:
empty :: Ord a => CustomSet a
```
The singleton redundancy makes sense, since you can make any value a
singleton set; it doesn't necessarily have to be Ord. Of course, you'll
find yourself unable to add other values to the set if it's not Ord, but
that's not `singleton`'s problem.
The empty redundancy makes sense as well, since an empty set can be a
set for any type, not necessarily ordered types. Ordering is only
required if the set may contain elements.
The `Eq` reduncancy is simply because `Ord` has already a constraint of
`Eq a => Ord a`.
This is true as of the current version:
https://hackage.haskell.org/package/base-4.8.2.0/docs/Data-Ord.html
and has been true since at least 4.0.0.0:
https://hackage.haskell.org/package/base-4.0.0.0/docs/Data-Ord.html
It was released about a month ago so it is prudent to start testing code with it. Blog post: https://ghc.haskell.org/trac/ghc/blog/ghc-8.0.1-released Migration: https://ghc.haskell.org/trac/ghc/wiki/Migration/8.0 Release notes: https://downloads.haskell.org/~ghc/8.0.1/docs/html/users_guide/8.0.1-notes.html
|
OK, 8.0.1 now (and commit message updated to indicate that it's been released, rather than pre-release as it was at the time I made this PR!) |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
It's a prerelease version, but it's likely to be good to start testing
against it now.
Two commits are needed to avoid compiler warnings on 8.0.1 (and thus errors since we use
-Werror). The errors that would appear are noted in the commit message.