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+%
+% (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
+%
+\section[SaLib]{Basic datatypes, functions for the strictness analyser}
+
+See also: the ``library'' for the ``back end'' (@SaBackLib@).
+
+\begin{code}
+#ifndef OLD_STRICTNESS
+module SaLib () where
+#else
+
+module SaLib (
+	AbsVal(..),
+	AnalysisKind(..),
+	AbsValEnv{-abstract-}, StrictEnv, AbsenceEnv,
+	mkAbsApproxFun,
+	nullAbsValEnv, addOneToAbsValEnv, growAbsValEnvList,
+	lookupAbsValEnv,
+	absValFromStrictness
+    ) where
+
+#include "HsVersions.h"
+
+import Type		( Type )
+import VarEnv
+import IdInfo		( StrictnessInfo(..) )
+import Demand		( Demand )
+import Outputable
+\end{code}
+
+%************************************************************************
+%*									*
+\subsection[AbsVal-datatype]{@AbsVal@: abstract values (and @AbsValEnv@)}
+%*									*
+%************************************************************************
+
+@AnalysisKind@ tells what kind of analysis is being done.
+
+\begin{code}
+data AnalysisKind
+  = StrAnal 	-- We're doing strictness analysis
+  | AbsAnal	-- We're doing absence analysis
+  deriving Show
+\end{code}
+
+@AbsVal@ is the data type of HNF abstract values.
+
+\begin{code}
+data AbsVal
+  = AbsTop		    -- AbsTop is the completely uninformative
+			    -- value
+
+  | AbsBot		    -- An expression whose abstract value is
+			    -- AbsBot is sure to fail to terminate.
+			    -- AbsBot represents the abstract
+			    --  *function* bottom too.
+
+  | AbsProd [AbsVal]	    -- (Lifted) product of abstract values
+			    -- "Lifted" means that AbsBot is *different* from
+			    --    AbsProd [AbsBot, ..., AbsBot]
+
+  | AbsFun	    	    -- An abstract function, with the given:
+	    Type	   	 -- Type of the *argument* to the function
+	    (AbsVal -> AbsVal)	-- The function
+
+  | AbsApproxFun	    -- This is used to represent a coarse
+	    [Demand]	    -- approximation to a function value.  It's an
+	    AbsVal	    -- abstract function which is strict in its
+			    -- arguments if the  Demand so indicates.
+	-- INVARIANT: the [Demand] is non-empty
+
+	-- AbsApproxFun has to take a *list* of demands, no just one,
+	-- because function spaces are now lifted.  Hence, (f bot top)
+	-- might be bot, but the partial application (f bot) is a *function*,
+	-- not bot.
+
+mkAbsApproxFun :: Demand -> AbsVal -> AbsVal
+mkAbsApproxFun d (AbsApproxFun ds val) = AbsApproxFun (d:ds) val
+mkAbsApproxFun d val	   	       = AbsApproxFun [d]    val
+
+instance Outputable AbsVal where
+    ppr AbsTop = ptext SLIT("AbsTop")
+    ppr AbsBot = ptext SLIT("AbsBot")
+    ppr (AbsProd prod) = hsep [ptext SLIT("AbsProd"), ppr prod]
+    ppr (AbsFun bndr_ty body) = ptext SLIT("AbsFun")
+    ppr (AbsApproxFun demands val)
+      = ptext SLIT("AbsApprox") <+> brackets (interpp'SP demands) <+> ppr val
+\end{code}
+
+%-----------
+
+An @AbsValEnv@ maps @Ids@ to @AbsVals@.  Any unbound @Ids@ are
+implicitly bound to @AbsTop@, the completely uninformative,
+pessimistic value---see @absEval@ of a @Var@.
+
+\begin{code}
+newtype AbsValEnv = AbsValEnv (IdEnv AbsVal)
+
+type StrictEnv  = AbsValEnv	-- Environment for strictness analysis
+type AbsenceEnv = AbsValEnv	-- Environment for absence analysis
+
+nullAbsValEnv -- this is the one and only way to create AbsValEnvs
+  = AbsValEnv emptyVarEnv
+
+addOneToAbsValEnv (AbsValEnv idenv) y z = AbsValEnv (extendVarEnv idenv y z)
+growAbsValEnvList (AbsValEnv idenv) ys  = AbsValEnv (extendVarEnvList idenv ys)
+
+lookupAbsValEnv (AbsValEnv idenv) y
+  = lookupVarEnv idenv y
+\end{code}
+
+\begin{code}
+absValFromStrictness :: AnalysisKind -> StrictnessInfo -> AbsVal
+
+absValFromStrictness anal NoStrictnessInfo = AbsTop
+absValFromStrictness anal (StrictnessInfo args_info bot_result)
+  = case args_info of	-- Check the invariant that the arg list on 
+	[] -> res	-- AbsApproxFun is non-empty
+	_  -> AbsApproxFun args_info res
+  where
+    res | not bot_result = AbsTop
+	| otherwise      = case anal of
+				StrAnal -> AbsBot
+				AbsAnal -> AbsTop
+\end{code}
+
+\begin{code}
+#endif /* OLD_STRICTNESS */
+\end{code}