X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FBase.lhs;h=2598583cbca667699d08a15c35353a479a8c5f91;hb=9da2d4c92821be09b27afa5b8bc1368b305a1496;hp=e3bc34665f08e14f2d33d389e094cdc1f1cb408b;hpb=c83f5ad9dbc5859bec565e4a6593c8cb105b5b64;p=ghc-base.git

diff --git a/GHC/Base.lhs b/GHC/Base.lhs
index e3bc346..2598583 100644
--- a/GHC/Base.lhs
+++ b/GHC/Base.lhs
@@ -597,6 +597,9 @@ lazy x = x
 
 -- Assertion function. This simply ignores its boolean argument.
 -- The compiler may rewrite it to (assertError line)
+-- 	SLPJ: in 5.04 etc 'assert' is in GHC.Prim,
+--	but from Template Haskell onwards it's simply
+--	defined here in Base.lhs
 assert :: Bool -> a -> a
 assert pred r = r
  
@@ -664,6 +667,29 @@ data (:*:) a b = a :*: b
 #endif
 \end{code}
 
+%*********************************************************
+%*							*
+\subsection{@getTag@}
+%*							*
+%*********************************************************
+
+Returns the 'tag' of a constructor application; this function is used
+by the deriving code for Eq, Ord and Enum.
+
+The primitive dataToTag# requires an evaluated constructor application
+as its argument, so we provide getTag as a wrapper that performs the
+evaluation before calling dataToTag#.  We could have dataToTag#
+evaluate its argument, but we prefer to do it this way because (a)
+dataToTag# can be an inline primop if it doesn't need to do any
+evaluation, and (b) we want to expose the evaluation to the
+simplifier, because it might be possible to eliminate the evaluation
+in the case when the argument is already known to be evaluated.
+
+\begin{code}
+{-# INLINE getTag #-}
+getTag :: a -> Int#
+getTag x = x `seq` dataToTag# x
+\end{code}
 
 %*********************************************************
 %*							*