From 3a7f204f5d713ed4ac034d371fc10d8bedb39efa Mon Sep 17 00:00:00 2001
From: Richard Eisenberg
Date: Sun, 10 Jan 2016 19:10:03 -0500
Subject: [PATCH] Clarify topological sorting of spec vars in manual
This is mentioned in #11376.
---
docs/users_guide/glasgow_exts.rst | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst
index 0ec5bd4f1c..e77a7c0243 100644
--- a/docs/users_guide/glasgow_exts.rst
+++ b/docs/users_guide/glasgow_exts.rst
@@ -2237,6 +2237,15 @@ Here are the details:
will have its type variables
ordered as ``m, a, b, c``.
+- If any of the variables depend on other variables (that is, if some
+ of the variables are *kind* variables), the variables are reordered
+ so that kind variables come before type variables, preserving the
+ left-to-right order as much as possible. That is, GHC performs a
+ stable topological sort on the variables.
+
+ For example: if we have ``bar :: Proxy (a :: (j, k)) -> b``, then
+ the variables are ordered ``j``, ``k``, ``a``, ``b``.
+
- Class methods' type arguments include the class type
variables, followed by any variables an individual method is polymorphic
in. So, ``class Monad m where return :: a -> m a`` means
--
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