lawbreakers in Text.PrettyPrint.HughesPJ

[Christian Maeder]

Simon Peyton-Jones wrote:
> It's a long time since I looked at this library.  If you two can agree
> on what needs to be done, I'll gladly execute the change!

I've tried both versions, without noticing a difference. So take the 
following patch (as suggested by Conal).

Cheers Christian


  -- 
---------------------------------------------------------------------------
  -- Vertical composition @$$@

-p $$  q = Above p False q
-p $+$ q = Above p True q
+above_ :: Doc -> Bool -> Doc -> Doc
+above_ Empty _ q = q
+above_ p _ Empty = p
+above_ p g q = Above p g q
+
+p $$  q = above_ p False q
+p $+$ q = above_ p True q

  above :: Doc -> Bool -> RDoc -> RDoc
  above (Above p g1 q1)  g2 q2 = above p g1 (above q1 g2 q2)
@@ -607,8 +611,13 @@
  -- 
---------------------------------------------------------------------------
  -- Horizontal composition @<>@

-p <>  q = Beside p False q
-p <+> q = Beside p True  q
+beside_ :: Doc -> Bool -> Doc -> Doc
+beside_ Empty _ q = q
+beside_ p _ Empty = p
+beside_ p g q = Beside p g q
+
+p <>  q = beside_ p False q
+p <+> q = beside_ p True  q

  beside :: Doc -> Bool -> RDoc -> RDoc
  -- Specification: beside g p q = p <g> q