Hi Norman,
Usually in the compiler Semigoup's <> is imported qualified. But I agree
it's ugly.
The trouble with Outputable's <> is that:
1) it doesn't have the same associativity as Semigroup's <>
2) <+> interacts weirdly with <> (cf
https://mail.haskell.org/pipermail/libraries/2011-November/017066.html)
I have rediscovered this when trying to fix it 2 months ago:
https://gitlab.haskell.org/hsyl20/ghc/-/commits/hsyl20/outputable-append
I have tried to add a new constructor to fix (2)
https://gitlab.haskell.org/hsyl20/ghc/-/commit/5d09acf4825a816ddb2ca2ec7294639b969ff64b
but it's still failing
(https://gitlab.haskell.org/hsyl20/ghc/-/jobs/791114).
Any help fixing these issues would be appreciated :)
Cheers,
Sylvain
On 14/12/2021 20:23, Norman Ramsey wrote:
I find myself wanting to define instances of Semigroup (and Monoid)
in a file that also imports GHC.Utils.Outputable and its `<>` operation
on SDocs. At the moment I am dealing with the incompatibility by
hiding the Outputable version and instead of writing `s1 <> s2` I write
`hcat [s1, s2]`. This workaround seems ugly and vaguely embarrassing.
How are others dealing with this issue? Would it be sensible simply
to make SDoc an instance of Semigroup (and Monoid), or would we be
concerned about potential additional overhead at compile time?
Norman
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