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Ryan Scott authored
Summary: When `-fprint-explicit-foralls` is enabled, type family equations are either printed without an explict `forall` entirely, or with a bizarre square bracket syntax (in the case of closed type families). I find neither satisfying, so in this patch, I introduce support for printing explicit `forall`s in open type-family, closed type-family, and data-family equations when appropriate. (By "when appropriate", I refer to the conditions laid out in `Note [When to print foralls]` in `IfaceType`.) One tricky point in the implementation is that I had to pick a visibility for each type variable in a `CoAxiom`/`FamInst` in order to be able to pass it to `pprUserIfaceForAll` //et al.// Because the type variables in a type family instance equation can't be instantiated by the programmer anyway, the choice only really matters for pretty-printing purposes, so I simply went with good ol' trustworthy `Specified`. (This design choice is documented in `Note [Printing foralls in type family instances]` in `IfaceType`.) Test Plan: make test TEST=T15827 Reviewers: goldfire, bgamari, simonpj Reviewed By: simonpj Subscribers: simonpj, rwbarton, carter GHC Trac Issues: #15827 Differential Revision: https://phabricator.haskell.org/D5282
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