Implement instance Data #614
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@clyring good catch. No particular reason, just a leftover from the previous PR. Reverted now. Since there are no internal invariants to uphold, I also added |
| gunfold k z c = case constrIndex c of | ||
| 1 -> k (z packBytes) | ||
| _ -> error "gunfold: unexpected constructor of strict ByteString" | ||
| dataTypeOf _ = byteStringDataType |
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The dataTypeOf change affects non-throwing traces. Major version bump?
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PVP does not prescribe this: somewhat surprisingly, it does not say anything about term-level changes. I deem this as a bug fix, not a change of intended semantics.
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The intent of the existing instance implementation is not so obvious. I do think this dataTypeOf change makes the instance more self-consistent and is an improvement.
But as a non-expert in the wider usage of Data I'm hesitant to put even small potentially-breaking changes into a minor release. And our users seem in no particular hurry to get working gread functionality.
The rest of the patch is fine for a minor release, of course.
PVP does not prescribe this: somewhat surprisingly, it does not say anything about term-level changes.
Right, the text of PVP mentions nothing on this subject. I'm reasonably sure that's an oversight. The graphical decision tree on the front page does have a node indicating that if "the behavior of any exported function change[d]," then a major version bump is necessary. The FAQ also provides an explicit example on this subject.
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I'm reasonably sure that's an oversight.
Neither FAQ nor decision tree (haskell/pvp#52) are normative. PVP is compile-time only. There was an attempt to change this (haskell/pvp#30), but it was withdrawn.
It's not a hill I want to die on, so if you feel strongly about it, I'll revert changes to dataTypeOf.
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No need to revert! The change is fine; I just think this should be where bytestring-0.12 finally diverges from master.
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@clyring any more suggestions? |
* Add functionality for toConstr * Other instances fixed * Move test * test passes * Add gshow tests * Typo * Add explicit string test * instance Data: implement gunfold and dataTypeOf * instance Data: fix tests * Fix emulated builds * Restore derived instance Data ShortByteString * Add instance Generic ShortByteString * Review suggestions --------- Co-authored-by: Colton Clemmer <coltonclemmerdev@gmail.com> (cherry picked from commit 1b9e6ec)
* Add functionality for toConstr * Other instances fixed * Move test * test passes * Add gshow tests * Typo * Add explicit string test * instance Data: implement gunfold and dataTypeOf * instance Data: fix tests * Fix emulated builds * Restore derived instance Data ShortByteString * Add instance Generic ShortByteString * Review suggestions --------- Co-authored-by: Colton Clemmer <coltonclemmerdev@gmail.com> (cherry picked from commit 1b9e6ec)
* Add functionality for toConstr * Other instances fixed * Move test * test passes * Add gshow tests * Typo * Add explicit string test * instance Data: implement gunfold and dataTypeOf * instance Data: fix tests * Fix emulated builds * Restore derived instance Data ShortByteString * Add instance Generic ShortByteString * Review suggestions --------- Co-authored-by: Colton Clemmer <coltonclemmerdev@gmail.com> (cherry picked from commit 1b9e6ec)
Fixes #513.
This is #519 rebased + tweaked tests. Thanks to @cbclemmer for trailblazing.