[Git][ghc/ghc][wip/T25647] Fix typos in documentation regarding wildcards in type families and clarify references

[Patrick (@soulomoon)]

Patrick pushed to branch wip/T25647 at Glasgow Haskell Compiler / GHC


Commits:
92ce46e4 by Patrick at 2025-03-05T10:54:49+08:00
Fix typos in documentation regarding wildcards in type families and clarify references

- - - - -


2 changed files:

- compiler/GHC/Core/TyCon.hs
- compiler/GHC/Tc/Gen/HsType.hs


Changes:

=====================================
compiler/GHC/Core/TyCon.hs
=====================================
@@ -2979,7 +2979,7 @@ tyConSkolem = isHoleName . tyConName
 -- not whether it is abstract or not.
 
 
-{- Note [WildCard in type families]
+{- Note [WildCards in type families]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Wildcards in type families are used to represent type/kind information that
 are not specified by the user. It is controversial how to interpret wildcards
@@ -3006,11 +3006,14 @@ explore different design spaces. For example, we can have the following design s
 3. Wildcards stand alone, pick skolemTv variables.
 ... and so on.
 
-Maintaining backward compatibility, the current picks:
+Maintaining backward compatibility from 8.6.4 to 9.10.2, the picks would be:
 - TyVarTv for FreeArg
 - TauTv for ClassArg
 - TauTv for SigArg
 
+See <More on SigArg> session in Note [FamArgFlavour] for why not just merge SigArg
+and ClassArg.
+
 For more discussion, see #13908.
 -}
 
@@ -3029,7 +3032,7 @@ We can conceptually view the kinds of arguments for a type family as a famArgFla
 with one flavour per argument of the family. Each flavour indicates whether the corresponding
 argument is a ClassArg or a FreeArg. We also introduce a third flavour, SigArg,
 to flag arguments that appear only in a kind signature for a type instance (i.e. when
-a wildcard is provided along with a kind annotation, as in @(_ :: _)@). See [More on SigArg]
+a wildcard is provided along with a kind annotation, as in @(_ :: _)@). See <More on SigArg>
 Session.
 
 Under the current design, when type-checking an instance the interpretation of wildcards
@@ -3047,7 +3050,7 @@ For instance, for an instance declaration like
 the first two underscores (free arguments) would yield TyVarTv’s while the last two underscores (a class
 argument and a signature argument) would produce TauTv's.
 
-[More on SigArg]
+<More on SigArg>
 Example from T14366
 
 type family F (a :: Type) :: Type where


=====================================
compiler/GHC/Tc/Gen/HsType.hs
=====================================
@@ -2265,6 +2265,7 @@ tcAnonWildCardOcc is_extra (TcTyMode { mode_holes = Just (hole_lvl, hole_mode) }
                       HM_FamPat ClassArg -> newTauTvDetailsAtLevel
                       HM_FamPat SigArg -> newTauTvDetailsAtLevel
                       _ -> newTauTvDetailsAtLevel
+                      -- see Note [WildCards in type families]
      emit_holes = case hole_mode of
                      HM_Sig       -> True
                      HM_FamPat _  -> False



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/92ce46e4a64611465a19698fd77dab15bfda64a3

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/92ce46e4a64611465a19698fd77dab15bfda64a3
You're receiving this email because of your account on gitlab.haskell.org.


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-commits/attachments/20250304/dd33f490/attachment-0001.html>