Changed logical order of requires and reads clauses on functions. Reads clauses

can now assume the precondition (as had also been the case back in the days when
reads clauses had to be self framing).

1 files changed, 13 insertions, 3 deletions

diff --git a/Test/dafny0/Reads.dfy b/Test/dafny0/Reads.dfy
index 7e0ca1c4..6dedbada 100644
--- a/Test/dafny0/Reads.dfy
+++ b/Test/dafny0/Reads.dfy
@@ -58,7 +58,7 @@ function ok5(r : R):()
 // Reads checking where there are circularities among the expressions
 
 class CircularChecking {
-  var Repr: set<object>
+  ghost var Repr: set<object>
     
   function F(): int
     reads this, Repr
@@ -76,8 +76,8 @@ class CircularChecking {
     requires Repr == {}
 
   function H0(cell: Cell): int
-    reads Repr  // error: reads is not self-framing (unless "this in Repr")
-    requires this in Repr  // lo and behold!  So, reads clause is fine, if we can assume the precondition
+    reads Repr  // by itself, this reads is not self-framing
+    requires this in Repr  // lo and behold!  So, reads clause is fine after all
 
   function H1(cell: Cell): int
     reads this, Repr
@@ -126,3 +126,13 @@ function FunctionInQuantifier2(): int
   var f: int -> int :| f.reads(10) == {} && f.requires(10) && f(10) == 100;  // fine :) :)
   f(10)
 }
+
+class DynamicFramesIdiom {
+  ghost var Repr: set<object>
+  predicate IllFormed_Valid()
+    reads Repr  // error: reads is not self framing (notice the absence of "this")
+  {
+    this in Repr  // this says that the predicate returns true if "this in Repr", but the
+                  // predicate can also be invoked in a state where its body will evaluate to false
+  }
+}