Commit 218dead0 authored by eir@cis.upenn.edu's avatar eir@cis.upenn.edu

Fix #8706, documenting that type operators are not promoted.

parent 312686c1
......@@ -6652,6 +6652,18 @@ See also <ulink url="http://ghc.haskell.org/trac/ghc/ticket/7347">Trac #7347</ul
</para>
</sect2>
<sect2>
<title>Promoting type operators</title>
<para>
Type operators are <emphasis>not</emphasis> promoted to the kind level. Why not? Because
<literal>*</literal> is a kind, parsed the way identifiers are. Thus, if a programmer
tried to write <literal>Either * Bool</literal>, would it be <literal>Either</literal>
applied to <literal>*</literal> and <literal>Bool</literal>? Or would it be
<literal>*</literal> applied to <literal>Either</literal> and <literal>Bool</literal>.
To avoid this quagmire, we simply forbid promoting type operators to the kind level.
</para>
</sect2>
</sect1>
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