#8888: Document Coercible in user's guide -------------------------------------+------------------------------------ Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.8.1 Component: Documentation | Version: 7.8.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by nomeata):
I'd welcome opinions from others.
Me too. Adding the cross-references you mention makes perfect sense, will do it in a moment.
So how does this even compile?
`coercibleTyCon` is added to `ghcPrimExports` in `PrelInfo`. I recall that when I was exporting it from `GHC.Types`, haddock would display it as a regular data type, not as a constraint. I now added this note: {{{ Note [Kind-changing of (~) and Coercible] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (~) and Coercible are tricky to define. To the user, they must appear as constraints, but we cannot define them as such in Haskell. But we also cannot just define them only in GHC.Prim (like (->)), because we need a real module for them, e.g. to compile the constructor's info table. Furthermore the type of MkCoercible cannot be written in Haskell (no syntax for ~#R). So we define them as regular data types in GHC.Types, but do /not/ export them. This ensures we have a home module. We then define them with the types and kinds that we actually want, in TysWiredIn, and export them in GHC.Prim. Haddock still takes the documentation from GHC.Types (and not from the fake module created from primops.txt.pp), so we have the user-facing documentation here. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8888#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler