[m-rev.] for review: Java: fix an assignment bug

[Michael Wybrow]

On Wed, 15 Jan 2003, Fergus Henderson wrote:
> 
> On 15-Jan-2003, Michael Wybrow <mjwybrow at cs.mu.OZ.AU> wrote:
> > 
> > mercury/compiler/mlds_to_java.m:
> >         Fix a bug in the Java back-end where incorrect code was being
> > 	generated for assignments if the Lval was a field with type 
> > 	enum_type.
> ...
> >  	( 
> > -		{ Lval = var(_, VarType) }, 
> > +		(
> > +			{ Lval = var(_, VarType) }
> > +		;
> > +			{ Lval = field(_, _, _, VarType, _) }
> > +		),
> >  	    	{ type_is_object(VarType) } 
> 
> That's OK, but the name "VarType" is misleading -- I suggest
> using "LvalType" instead.
> 
> Also, a more robust (future-proof) way of writing it would be
> to extract the code for computing an lval's type out into
> a separate subroutine with determinism `det'.

In that case, you'll probably have no problems in signing off on
the following diff instead -- it's mostly yours, though I did
correct a missing parenthesis in your sample code.  :-)


Index: mlds_to_java.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/mlds_to_java.m,v
retrieving revision 1.33
diff -u -r1.33 mlds_to_java.m
--- mlds_to_java.m	24 Nov 2002 03:57:26 -0000	1.33
+++ mlds_to_java.m	16 Jan 2003 04:36:29 -0000
@@ -162,6 +162,19 @@
 	; Builtin = user_type 
 	).
 
+	% Given an lval, return its type.
+	% 
+:- func mlds_lval_type(mlds__lval) = mlds__type.
+
+mlds_lval_type(var(_, VarType)) = VarType.
+mlds_lval_type(field(_, _, _, FieldType, _)) = FieldType.
+mlds_lval_type(mem_ref(_, PtrType)) =
+	( PtrType = mlds__ptr_type(Type) ->
+		Type
+	;
+		func_error("mlds_lval_type: mem_ref of non-pointer")
+	).
+
 	% Succeeds iff the Rval represents an integer constant.  
 	%
 :- pred rval_is_int_const(mlds__rval).
@@ -2448,15 +2461,14 @@
 	output_lval(Lval),
 	io__write_string(" = "),
 	( 
-		{ Lval = var(_, VarType) }, 
-	    	{ type_is_object(VarType) } 
-	    
+		{ LvalType = mlds_lval_type(Lval) },
+	    	{ type_is_object(LvalType) }
 	->
 		% If the Lval is a an object.	
 		
 		( { rval_is_int_const(Rval) } ->
 			io__write_string("new "),
-			output_type(VarType),
+			output_type(LvalType),
 			io__write_string("("),
 			output_rval(Rval),
 			io__write_string(")")

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