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| author | Ryan Scott <ryan.gl.scott@gmail.com> | 2023-02-12 08:42:23 -0500 |
|---|---|---|
| committer | Ryan Scott <ryan.gl.scott@gmail.com> | 2023-02-20 20:44:35 -0500 |
| commit | ff8e99f69b203559b784014ab26c59b5553d128a (patch) | |
| tree | 6a997080020bfb1d217861df268f830311467ce1 /compiler/GHC/Rename/Module.hs | |
| parent | 96dc58b9225d91a7912957c6be5d9c7a95e51718 (diff) | |
| download | haskell-wip/T22948.tar.gz | |
Disallow `tagToEnum#` on `type data` typeswip/T22948
We don't want to allow users to conjure up values of a `type data` type using
`tagToEnum#`, as these simply don't exist at the value level.
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) |