From e11c554e94c39223ea55991a552ccb244dfe4364 Mon Sep 17 00:00:00 2001 From: Adam Megacz Date: Fri, 22 Apr 2011 20:22:06 -0700 Subject: [PATCH] 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 --- compiler/prelude/primops.txt.pp | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) 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, -- 1.7.10.4