[Git][ghc/ghc][wip/T25647] Enhance documentation on FamArgFlavour handling in type families and clarify...

[Patrick (@soulomoon)]

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


Commits:
6ab0b7c9 by Patrick at 2025-03-05T20:40:21+08:00
Enhance documentation on FamArgFlavour handling in type families and clarify implementation details in TyCon and HsType modules

- - - - -


2 changed files:

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


Changes:

=====================================
compiler/GHC/Core/TyCon.hs
=====================================
@@ -3053,6 +3053,12 @@ 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.
 
+<Implemenation Detail>
+The ClassArg and FreeArg are generated in `mkFamilyTyCon` and store at `famTcParent` field at `FamilyTyCon`.
+When typechecking type families, the `FamArgFlavour's passed in `tcAnonWildCardOcc` when dancing around
+inside `tcInferTyApps` and `SigArg` is passed down at `HsKindSig` branch of `tcHsType` in the dance.
+
+
 <More on SigArg>
 Example from T14366
 


=====================================
compiler/GHC/Tc/Gen/HsType.hs
=====================================
@@ -1286,6 +1286,7 @@ tcHsType mode rn_ty@(HsOpTy{})      exp_kind = tc_app_ty mode rn_ty exp_kind
 
 tcHsType mode rn_ty@(HsKindSig _ ty sig) exp_kind
   = do { let mode' = (updateFamArgFlavour SigArg $ mode { mode_tyki = KindLevel})
+        --  see Note [FamArgFlavour]
        ; traceTc "tcHsType:sig0" (ppr ty <+> ppr (mode_holes mode'))
        ; sig' <- tc_lhs_kind_sig mode' KindSigCtxt sig
                  -- We must typecheck the kind signature, and solve all
@@ -1578,7 +1579,7 @@ tcInferTyApps, tcInferTyApps_nosat
     -> LHsType GhcRn        -- ^ Function (for printing only)
     -> TcType               -- ^ Function
     -> [LHsTypeArg GhcRn]   -- ^ Args
-    -> [FamArgFlavour]   -- ^ Args
+    -> [FamArgFlavour]      -- ^ Args flavours see Note [FamArgFlavour] and
     -> TcM (TcType, TcKind) -- ^ (f args, result kind)
 tcInferTyApps mode hs_ty fun hs_args famArgFlvs
   = do { (f_args, res_k) <- tcInferTyApps_nosat mode hs_ty fun hs_args famArgFlvs



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/6ab0b7c9a0edd1931a456166320b73b72a037b1b

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/6ab0b7c9a0edd1931a456166320b73b72a037b1b
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