diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/glasgow_exts.xml | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml index 393cbf50ac..2883757fc0 100644 --- a/docs/users_guide/glasgow_exts.xml +++ b/docs/users_guide/glasgow_exts.xml @@ -2002,9 +2002,9 @@ of the data constructor. For GADTs, the field may mention only types that appear as a simple type-variable argument in the constructor's result type</emphasis>. For example: <programlisting> -data T a where { T1 { f1::a, f2::(a,b) } :: T a } -- b is existential -upd1 t x = t { f1=x } -- OK: upd1 :: T a -> b -> T b -upd2 t x = t { f2=x } -- BAD (f2's type mentions b, which is +data T a b where { T1 { f1::a, f2::b, f3::(b,c) } :: T a b } -- c is existential +upd1 t x = t { f1=x } -- OK: upd1 :: T a b -> a' -> T a' b +upd2 t x = t { f3=x } -- BAD (f3's type mentions c, which is -- existentially quantified) data G a b where { G1 { g1::a, g2::c } :: G a [c] } |