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class List[T] {
var list: seq[T]
constructor Empty()
ensures list = []
constructor Singleton(t: T)
ensures list = [t]
constructor Double(p: T, q: T)
ensures list = [p q]
}
model List[T] {
var root: Node[T]
frame
root
invariant
root = null ==> |list| = 0
root != null ==> list = root.list
}
class Node[T] {
var list: seq[T]
invariant
|list| > 0
constructor Init(t: T)
ensures list = [t]
constructor Double(p: T, q: T)
ensures list = [p q]
method List() returns (lst: seq[T])
requires |list| = 1
ensures lst = list
method Tail() returns (tail: Node[T])
ensures |list| = 1 ==> tail = null
ensures |list| > 1 ==> tail != null && tail.list = list[1..]
method SkipFew(num: int) returns (ret: Node[T])
requires num >= 0
ensures num >= |list| ==> ret = null
ensures num < |list| ==> ret != null && ret.list = list[num..]
method Get(idx: int) returns (ret: T)
requires idx >= 0 && idx < |list|
requires idx >= 1 && next != null
ensures ret = list[idx]
}
model Node[T] {
var data: T
var next: Node[T]
frame
next
invariant
next = null ==> list = [data]
next != null ==> list = [data] + next.list
}
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