[commit: ghc] master: Document that type holes kill polymorphic recursion (ca47186)
git at git.haskell.org
git at git.haskell.org
Thu Jul 27 11:50:03 UTC 2017
Repository : ssh://git@git.haskell.org/ghc
On branch : master
Link : http://ghc.haskell.org/trac/ghc/changeset/ca471860494484210b6291dd96d1e0868da750e7/ghc
>---------------------------------------------------------------
commit ca471860494484210b6291dd96d1e0868da750e7
Author: Richard Eisenberg <rae at cs.brynmawr.edu>
Date: Tue Jul 18 15:55:21 2017 -0400
Document that type holes kill polymorphic recursion
This "fixes" #11995.
>---------------------------------------------------------------
ca471860494484210b6291dd96d1e0868da750e7
docs/users_guide/glasgow_exts.rst | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst
index 7fc075a..b0da2891 100644
--- a/docs/users_guide/glasgow_exts.rst
+++ b/docs/users_guide/glasgow_exts.rst
@@ -10290,6 +10290,10 @@ warnings instead of errors. Additionally, these warnings can be silenced
with the :ghc-flag:`-Wno-partial-type-signatures <-Wpartial-type-signatures>`
flag.
+However, because GHC must *infer* the type when part of a type is left
+out, it is unable to use polymorphic recursion. The same restriction
+takes place when the type signature is omitted completely.
+
.. _pts-syntax:
Syntax
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