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Diffstat (limited to 'compiler/GHC/Rename/Module.hs')
| -rw-r--r-- | compiler/GHC/Rename/Module.hs | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/compiler/GHC/Rename/Module.hs b/compiler/GHC/Rename/Module.hs index e9b8d40d83..fd9792744c 100644 --- a/compiler/GHC/Rename/Module.hs +++ b/compiler/GHC/Rename/Module.hs @@ -2169,6 +2169,17 @@ The main parts of the implementation are: * In `GHC.Core.Utils.refineDataAlt`, do /not/ fill in the DEFAULT case with the data constructor. See Note [Refine DEFAULT case alternatives] Exception 2, in GHC.Core.Utils. + +* To prevent users from conjuring up `type data` values at the term level, we + disallow using the tagToEnum# function on a type headed by a `type data` + type. For instance, GHC will reject this code: + + type data Letter = A | B | C + + f :: Letter + f = tagToEnum# 0# + + See `GHC.Tc.Gen.App.checkTagToEnum`, specifically `check_enumeration`. -} warnNoDerivStrat :: Maybe (LDerivStrategy GhcRn) |