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+%
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1994
+%
+\section[DefSyn]{A temporary datatype for the deforestation pass}
+
+> module DefSyn where
+
+> import CoreSyn
+> import Outputable
+> import Util
+
+This is exactly the same as core, except that the argument to
+application can be an arbitrary expression.
+
+> type DefProgram 		= [CoreBinding 	Id DefBindee]
+> type DefBinding 		= CoreBinding  	Id DefBindee
+> type DefExpr    		= CoreExpr     	Id DefBindee
+> type DefAtom    		= CoreAtom	DefBindee
+> type DefCaseAlternatives	= CoreCaseAlternatives Id DefBindee
+> type DefCaseDefault		= CoreCaseDefault Id DefBindee
+
+> type DefCoreArg = CoreArg DefBindee
+
+> data DefBindee 
+> 	= DefArgExpr DefExpr		-- arbitrary expressions as argumemts
+>	| DefArgVar  Id			-- or just ids
+>	| Label DefExpr DefExpr		-- labels for detecting cycles
+
+
+Ok, I've cheated horribly here.  Instead of defining a new data type
+including the new Label construct, I've just defined a new
+parameterisation of Core in which a variable can be one of {variable,
+expression, label}.  This gives us both arbitrary expressions on the
+right hand side of application, in addition to the new Label
+construct.
+
+The penalty for this is that expressions will have extra indirections
+as compared with a new datatype.  The saving is basically not having
+to define a new datatype almost identical to Core.
+
+Because our parameterised datatype is a little too general (i.e. it
+distinguishes expressions that we wish to equate), there are some
+invariants that will be adhered to during the transformation.  The
+following are alternative representations for certain expressions.
+The forms on the left are disallowed:
+
+CoVar (DefArgExpr e)	==  e
+CoVarAtom (Label l e)	==  CoVarAtom (DefArgExpr (CoVar (Label l e)))
+
+For completeness, we should also have:
+
+CoVarAtom (DefArgVar v) == CoVarAtom (DefArgExpr (CoVar (DefArgVar v)))
+CoLitAtom l		== CoVarAtom (DefArgExpr (CoLit l))
+
+In other words, atoms must all be of the form (CoVarAtom (DefArgExpr
+_)) and the argument to a CoVar can only be Label or DefArgVar.
+
+> mkLabel :: DefExpr -> DefExpr -> DefExpr
+> mkLabel l e = CoVar (Label l e)