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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2012-08-20 14:26:08 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2012-08-20 14:26:08 +0100 |
| commit | 00a2104b75b664026a44b26c73cc971f9733fbaa (patch) | |
| tree | cf2490f4068e18f14faea1546273cf35a09b5412 /docs/users_guide | |
| parent | 41c7342e7937dab55d082a0c5612f783e7eaa855 (diff) | |
| download | haskell-00a2104b75b664026a44b26c73cc971f9733fbaa.tar.gz | |
Improve documentation for rank-1 types (Trac #7137)
Diffstat (limited to 'docs/users_guide')
| -rw-r--r-- | docs/users_guide/glasgow_exts.xml | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml index a4fb7c246c..04f6f67339 100644 --- a/docs/users_guide/glasgow_exts.xml +++ b/docs/users_guide/glasgow_exts.xml @@ -6384,7 +6384,7 @@ The function <literal>f3</literal> has a rank-3 type; it has rank-2 types on the left of a function arrow. </para> <para> -GHC has three flags to control higher-rank types: +GHC has three flags to control higher-rank types. (All three imply <option>-XExplicitForAll</option>, <xref linkend="explicit-foralls"/>.) <itemizedlist> <listitem><para> <option>-XPolymorphicComponents</option>: data constructors (only) can have polymorphic argument types. @@ -6409,9 +6409,13 @@ field type signatures.</para> </listitem> </itemizedlist> </para></listitem> </itemizedlist> +Either <option>-XRank2Types</option> or <option>-XRankNTypes</option> is also required for any +type with a <literal>forall</literal> or +context to the right of an arrow (e.g. <literal>f :: Int -> forall a. a->a</literal>, or +<literal>g :: Int -> Ord a => a -> a</literal>). Such types are technically rank 1, but +are clearly not Haskell-98, and an extra flag did not seem worth the bother. </para> - <sect3 id="univ"> <title>Examples </title> |