diff options
Diffstat (limited to 'docs/users_guide')
| -rw-r--r-- | docs/users_guide/glasgow_exts.xml | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml index 5c4b091f30..1366197654 100644 --- a/docs/users_guide/glasgow_exts.xml +++ b/docs/users_guide/glasgow_exts.xml @@ -6387,9 +6387,10 @@ class (F a ~ b) => C a b where type <literal>(Show a, Ord a)</literal> is of kind <literal>Constraint</literal>. </listitem> <listitem> - Anything whose form is not yet know, but the user has declared to have kind <literal>Constraint</literal>. - So for example <literal>type Foo (f :: * -> Constraint) = forall b. f b => b -> b</literal> is allowed, as - well as examples involving type families: + Anything whose form is not yet know, but the user has declared to have kind <literal>Constraint</literal> + (for which they need to import it from <literal>GHC.Exts</literal>). So for example + <literal>type Foo (f :: * -> Constraint) = forall b. f b => b -> b</literal> is allowed, as well as + examples involving type families: <programlisting> type family Typ a b :: Constraint type instance Typ Int b = Show b |