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Diffstat (limited to 'docs/users_guide/using.rst')
| -rw-r--r-- | docs/users_guide/using.rst | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/docs/users_guide/using.rst b/docs/users_guide/using.rst index 23e0e1d1b8..d2983c4b1a 100644 --- a/docs/users_guide/using.rst +++ b/docs/users_guide/using.rst @@ -821,6 +821,37 @@ messages and in GHCi: kinds, GHC uses type-level coercions. Users will rarely need to see these, as they are meant to be internal. +.. ghc-flag:: -fprint-axiom-incomps + :shortdesc: Display equation incompatibilities in closed type families + :type: dynamic + :reverse: -fno-print-axiom-incomps + :category: verbosity + + Using :ghc-flag:`-fprint-axiom-incomps` tells GHC to display + incompatibilities between closed type families' equations, whenever they + are printed by :ghci-cmd:`:info` or :ghc-flag:`--show-iface ⟨file⟩`. + + .. code-block:: none + + ghci> :i Data.Type.Equality.== + type family (==) (a :: k) (b :: k) :: Bool + where + (==) (f a) (g b) = (f == g) && (a == b) + (==) a a = 'True + (==) _1 _2 = 'False + ghci> :set -fprint-axiom-incomps + ghci> :i Data.Type.Equality.== + type family (==) (a :: k) (b :: k) :: Bool + where + (==) (f a) (g b) = (f == g) && (a == b) + (==) a a = 'True + -- incompatible indices: 0 + (==) _1 _2 = 'False + -- incompatible indices: 1, 0 + + The comment after each equation refers to the indices (0-indexed) of + preceding equations it is incompatible with. + .. ghc-flag:: -fprint-equality-relations :shortdesc: Distinguish between equality relations when printing :type: dynamic |