From: Adam Megacz <megacz@cs.berkeley.edu>
Date: Sat, 23 Apr 2011 03:22:06 +0000 (-0700)
Subject: primops.txt.pp: add missing type application in description of GHC.Prim.Any
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=e11c554e94c39223ea55991a552ccb244dfe4364;hp=51bbdda993815fc0c3e55cbfcc60ffd512b9d4bd

primops.txt.pp: add missing type application in description of GHC.Prim.Any

Understanding GHC.Prim.Any is all about understanding the need for
explicit type applications in CoreSyn; the previous example had one
explicit type application but was missing the other, which this patch
adds.  It also expands the explanation, based on SPJ's post here:

  http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/46551
---

diff --git a/compiler/prelude/primops.txt.pp b/compiler/prelude/primops.txt.pp
index 7d80db4..49f7a97 100644
--- a/compiler/prelude/primops.txt.pp
+++ b/compiler/prelude/primops.txt.pp
@@ -1738,9 +1738,19 @@ primtype Any a
 	    but never enters a function value.  
 
 	It's also used to instantiate un-constrained type variables after type
-	checking.  For example
+	checking.  For example, {\tt length} has type
 
-	{\tt length Any []}
+	{\tt length :: forall a. [a] -> Int}
+
+	and the list datacon for the empty list has type
+
+	{\tt [] :: forall a. [a]}
+
+	In order to compose these two terms as {\tt length []} a type
+	application is required, but there is no constraint on the
+	choice.  In this situation GHC uses {\tt Any}:
+
+	{\tt length Any ([] Any)}
 
 	Annoyingly, we sometimes need {\tt Any}s of other kinds, such as {\tt (* -> *)} etc.
 	This is a bit like tuples.   We define a couple of useful ones here,