From: Malcolm.Wallace@cs.york.ac.uk <unknown>
Date: Tue, 22 Apr 2008 13:05:47 +0000 (+0000)
Subject: Improve docs for unsafeCoerce
X-Git-Tag: 2008-05-28~15
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=c842bdaa7756a98584ff780773addc426c3ff150;p=ghc-base.git

Improve docs for unsafeCoerce
Make it clear that compilers differ.  Point to GHC docs in GHC.Base, and
add a short description of nhc98's representation-safe conversions.
---

diff --git a/Unsafe/Coerce.hs b/Unsafe/Coerce.hs
index 00444bd..e911c6f 100644
--- a/Unsafe/Coerce.hs
+++ b/Unsafe/Coerce.hs
@@ -14,8 +14,16 @@
 -- it is your responsibility to ensure that the old and new types have
 -- identical internal representations, in order to prevent runtime corruption.
 --
--- 'unsafeCoerce' is just a trivial wrapper for 'unsafeCoerce#';
--- see the latter for important documentation about correct usage.
+-- The types for which 'unsafeCoerce' is representation-safe may differ
+-- from compiler to compiler (and version to version).
+--
+--   * Documentation for correct usage in GHC will be found under
+--     'unsafeCoerce#' in GHC.Base (around which 'unsafeCoerce' is just a
+--     trivial wrapper).
+--
+--   * In nhc98, the only representation-safe coercions are between Enum
+--     types with the same range (e.g. Int, Int32, Char, Word32),
+--     or between a newtype and the type that it wraps.
 
 module Unsafe.Coerce (unsafeCoerce) where