[project @ 1999-05-11 16:42:54 by keithw]

(this is number 6 of 9 commits to be applied together)

  It is useful to know the usage of a lambda outside the usage
  inference (specifically, in the simplifier); thus as a temporary
  hack to make this information available without undue modification
  to the rest of the compiler, the information is copied into the
  IdInfo field of the binder.

  The new information is LBVarInfo, which can be either NoLBVarInfo or
  IsOneShotLambda, corresponding to __m/no info and __o respectively.
  LBVarInfo is not intended to be printed in interface files; to
  enforce this ppLBVarInfo is defined to print nothing.

ghc/compiler/basicTypes/IdInfo.lhs

@@ -49,7 +49,10 @@ module IdInfo (
 	CafInfo(..), cafInfo, setCafInfo, ppCafInfo,
 
         -- Constructed Product Result Info
-        CprInfo(..), cprInfo, setCprInfo, ppCprInfo, noCprInfo
+        CprInfo(..), cprInfo, setCprInfo, ppCprInfo, noCprInfo,
+
+        -- Lambda-bound variable info
+        LBVarInfo(..), lbvarInfo, setLBVarInfo, noLBVarInfo,
     ) where
 
 #include "HsVersions.h"
@@ -61,6 +64,7 @@ import {-# SOURCE #-} CoreSyn	 ( CoreExpr )
 import Var              ( Id )
 import SpecEnv	        ( SpecEnv, emptySpecEnv )
 import Demand		( Demand,  isLazy, wwLazy, pprDemands )
+import Type             ( UsageAnn )
 import Outputable	
 
 import Maybe            ( isJust )
@@ -77,7 +81,8 @@ the properties attached to the other.
 
 The @IdInfo@ gives information about the value, or definition, of the
 @Id@.  It does {\em not} contain information about the @Id@'s usage
-(except for @DemandInfo@? ToDo).
+(except for @DemandInfo@? ToDo). (@lbvarInfo@ is also a marginal
+case.  KSW 1999-04).
 
 \begin{code}
 data IdInfo
@@ -91,6 +96,7 @@ data IdInfo
 	updateInfo :: UpdateInfo,		-- Which args should be updated
 	cafInfo :: CafInfo,
 	cprInfo :: CprInfo,                     -- Function always constructs a product result
+        lbvarInfo :: LBVarInfo,			-- Info about a lambda-bound variable
 	inlinePragInfo :: !InlinePragInfo	-- Inline pragmas
     }
 \end{code}
@@ -108,6 +114,7 @@ setInlinePragInfo pr info = info { inlinePragInfo = pr }
 setUnfoldingInfo  uf info = info { unfoldingInfo = uf }
 setCafInfo        cf info = info { cafInfo = cf }
 setCprInfo        cp info = info { cprInfo = cp }
+setLBVarInfo      lb info = info { lbvarInfo = lb }
 \end{code}
 
 
@@ -122,6 +129,7 @@ noIdInfo = IdInfo {
 		updateInfo	= NoUpdateInfo,
 		cafInfo		= MayHaveCafRefs,
 		cprInfo		= NoCPRInfo,
+                lbvarInfo       = NoLBVarInfo,
 		inlinePragInfo  = NoInlinePragInfo
 	   }
 \end{code}
@@ -488,4 +496,43 @@ instance Show CprInfo where
 \end{code}
 
 
+%************************************************************************
+%*									*
+\subsection[lbvar-IdInfo]{Lambda-bound var info about an @Id@}
+%*									*
+%************************************************************************
 
+If the @Id@ is a lambda-bound variable then it may have lambda-bound
+var info.  The usage analysis (UsageSP) detects whether the lambda
+binding this var is a ``one-shot'' lambda; that is, whether it is
+applied at most once.
+
+This information may be useful in optimisation, as computations may
+safely be floated inside such a lambda without risk of duplicating
+work.
+
+\begin{code}
+data LBVarInfo
+  = NoLBVarInfo
+
+  | IsOneShotLambda			-- the lambda that binds this Id is applied
+					--   at most once
+				-- HACK ALERT! placing this info here is a short-term hack,
+				--   but it minimises changes to the rest of the compiler.
+				--   Hack agreed by SLPJ/KSW 1999-04.
+\end{code}
+
+\begin{code}
+
+noLBVarInfo = NoLBVarInfo
+
+-- not safe to print or parse LBVarInfo because it is not really a
+-- property of the definition, but a property of the context.
+ppLBVarInfo _ = empty
+
+instance Outputable LBVarInfo where
+    ppr = ppLBVarInfo
+
+instance Show LBVarInfo where
+    showsPrec p c = showsPrecSDoc p (ppr c)
+\end{code}