Added a couple more tests for checkUnusedVar which has revealed two bugs

One of these bugs is that array variables are counted as unused when they are used subscripted.  I think that should be solved when we flip back to the listify approach.

The second bug is more interesting, as it is triggered only in a certain arrangement with an IF.  It's either a bug in the flow-graph building or in the varsTouchedAfter code.

checks/CheckTest.hs

@@ -54,6 +54,39 @@ testUnusedVar = TestList
         [decl (return A.Int) oX []]
       `becomes`
       oSEQ []
+
+  ,testSame "Used array variable" $ wrap $
+    oSEQ [
+      decl (return $ A.Array [A.Dimension $ intLiteral 2] A.Int) oX
+        [oX `sub` 0 *:= (return (0::Int))]
+    ]
+
+  ,testSame "One variable, used in one IF branch" $ wrap $
+    oSEQ [
+      decl (return A.Int) oX
+        [oIF
+          [ifChoice (True, oX *:= (return (0::Int)))
+          ,ifChoice (True, oSKIP)
+          ]
+        ]
+    ]
+  ,testSame "One variable, declared in an IF and used in one IF branch" $ wrap $
+       oIF
+       [
+         decl (return A.Int) oX       
+          [ifChoice (True, oX *:= (return (0::Int)))
+          ,ifChoice (True, oSKIP)
+          ]
+       ]
+  ,testSame "One variable, declared in an IF and used in second IF branch" $ wrap $
+       oIF
+       [
+         decl (return A.Int) oX       
+          [ifChoice (True, oSKIP)
+          ,ifChoice (True, oX *:= (return (0::Int)))
+          ]
+       ]
+
  ]
  where
    wrap x = oPROC "foo" [] x oempty

common/OccamEDSL.hs

@@ -23,6 +23,7 @@ module OccamEDSL (ExpInp, ExpInpT,
   oALT, guard,
   oIF, ifChoice,
   Occ, oA, oB, oC, oX, oY, oZ, p0, p1, p2, (*?), (*!), (*:=), (*+), decl, decl', decl'',
+    sub,
     oempty, testOccamPass,
     oprocess,
     testOccamPassWarn, testOccamPassTransform, ExpInpC(shouldComeFrom),
@@ -292,6 +293,10 @@ infix 8 *:=
               return (A.Dyadic emptyMeta A.Add x' y')
 
 
+sub :: ExpInp A.Variable -> Int -> ExpInp A.Variable
+sub v n = liftM (A.SubscriptedVariable emptyMeta (A.Subscript emptyMeta A.CheckBoth
+  $ intLiteral $ toInteger n)) v
+
 decl :: Data a => ExpInp A.Type -> ExpInp A.Variable ->
   [O (A.Structured a)] -> O (A.Structured a)
 decl bty bvar scope = do