Created
October 9, 2015 23:46
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// class Node | |
field left: Ref | |
field right: Ref | |
field is_marked: Bool | |
predicate inv(node: Ref, graph: Set[Ref]) { | |
node != null | |
&& acc(node.left) | |
&& acc(node.right) | |
&& acc(node.is_marked) | |
&& (node.left != null ==> acc(inv(node.left, graph))) | |
&& (node.right != null ==> acc(inv(node.right, graph))) | |
&& node in graph | |
&& (forall a: Ref :: a in graph ==> acc(a.left)) | |
&& (forall b: Ref :: b in graph ==> acc(b.right)) | |
&& (forall c: Ref :: c in graph ==> acc(c.is_marked)) | |
&& (forall x: Ref :: x in graph ==> (x.left != null ==> x.left in graph)) | |
&& (forall y: Ref :: y in graph ==> (y.right != null ==> y.right in graph)) | |
} | |
method reach(graph: Set[Ref], node: Ref) returns (reached: Set[Ref]) | |
requires acc(inv(node, graph)) | |
ensures acc(inv(node, graph)) | |
//TODO: ensures acc(inv(node, reached)) | |
{ | |
unfold acc(inv(node, graph)) | |
var left_reached: Set[Ref] := Set[Ref]() | |
if (node.left != null && !node.left.is_marked) { | |
node.left.is_marked := true | |
left_reached := reach(graph, node.left) | |
} | |
var right_reached: Set[Ref] := Set[Ref]() | |
if (node.right != null && !node.right.is_marked) { | |
node.right.is_marked := true | |
right_reached := reach(graph, node.right) | |
} | |
reached := (left_reached) union Set(node) union (right_reached) | |
fold acc(inv(node, graph)) | |
} |
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