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strengthen postcondition on 007 (substring filtering)
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Original file line number | Diff line number | Diff line change |
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@@ -36,10 +36,16 @@ fn string_eq(s1: &str, s2: &str) -> (result: bool) | |
true | ||
} | ||
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spec fn is_subseq_of<A>(s: Seq<A>, sub: Seq<A>) -> bool { | ||
exists|i: int| 0 <= i <= s.len() - sub.len() && s.subrange(i, #[trigger] (i + sub.len())) == sub | ||
} | ||
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fn check_substring(s: &str, sub: &str) -> (result: bool) | ||
ensures | ||
result <==> exists|i: int| | ||
0 <= i <= s@.len() - sub@.len() && s@.subrange(i, #[trigger] (i + sub@.len())) == sub@, | ||
result <==> is_subseq_of(s@, sub@), | ||
// exists|i: int| | ||
// 0 <= i <= [email protected]() - [email protected]() && [email protected](i, #[trigger] (i + [email protected]())) == sub@, | ||
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{ | ||
let s_len = s.unicode_len(); | ||
let sub_len = sub.unicode_len(); | ||
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@@ -66,32 +72,64 @@ fn check_substring(s: &str, sub: &str) -> (result: bool) | |
false | ||
} | ||
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fn filter_by_substring<'a>(strings: &Vec<&'a str>, substring: &str) -> (res: Vec<&'a str>) | ||
fn filter_by_sub<'a>(strings: &Vec<&'a str>, sub: &str) -> (res: Vec<&'a str>) | ||
ensures | ||
forall|i: int| | ||
0 <= i < strings@.len() && (exists|j: int| | ||
0 <= j <= strings@[i]@.len() - substring@.len() && strings[i]@.subrange( | ||
j, | ||
#[trigger] (j + substring@.len()), | ||
) == substring@) ==> res@.contains(#[trigger] (strings[i])), | ||
strings@.filter(|s: &str| is_subseq_of(s@, sub@)) | ||
== res@, | ||
// forall|i: int| | ||
// 0 <= i < [email protected]() && | ||
// // [email protected] (|s: &str| is_subseq_of(s@, sub@)) == res@ | ||
// is_subseq_of(strings[i]@, sub@) ==> [email protected]( | ||
// #[trigger] (strings[i]), | ||
// ) && [email protected](#[trigger] (strings[i])) ==> is_subseq_of(strings[i]@, sub@), | ||
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{ | ||
let mut res = Vec::new(); | ||
// assert ([email protected](0, 0).filter (|s: &str| is_subseq_of(s@, sub@)) == res@); | ||
assert(res@ == Seq::<&str>::empty()); | ||
let mut n = 0; | ||
// while n < strings.len() | ||
for n in 0..strings.len() | ||
invariant | ||
forall|i: int| | ||
0 <= i < n && (exists|j: int| | ||
0 <= j <= strings@[i]@.len() - substring@.len() && strings[i]@.subrange( | ||
j, | ||
#[trigger] (j + substring@.len()), | ||
) == substring@) ==> res@.contains(#[trigger] (strings[i])), | ||
// n < strings.len(), | ||
// forall|i: int| | ||
// 0 <= i < n && is_subseq_of(strings[i]@, sub@) ==> [email protected]( | ||
// #[trigger] (strings[i]), | ||
// ), | ||
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strings@.subrange(0, n as int).filter(|s: &str| is_subseq_of(s@, sub@)) == res@, | ||
n <= strings.len(), | ||
{ | ||
if check_substring(strings[n], substring) { | ||
let ghost res_old = res; | ||
reveal(Seq::filter); | ||
assert(strings@.subrange(0, n as int + 1).drop_last() == strings@.subrange(0, n as int)); | ||
if check_substring(strings[n], sub) { | ||
// let ghost res_old = res@; | ||
// let ghost filtered_sub = [email protected](0, n as int).filter (|s: &str| is_subseq_of(s@, sub@)); | ||
// let ghost pred = |s: &str| is_subseq_of(s@, sub@); | ||
// let ghost last = ran.last(); | ||
// assert (last@ == strings[n as int]@); | ||
// let ghost ra = ran.drop_last(); | ||
// assert(ra.push(last) == ran); | ||
// assert (ra == [email protected](0, n as int)); | ||
// assert (pred(last)); | ||
// let ghost ran_f = ran.filter(pred); | ||
// let ghost ra_f = ra.filter(pred); | ||
// assert(ra_f == res@); | ||
// assert(ra_f.push(last) == ran_f); | ||
// assert (ran.filter (|s: &str| is_subseq_of(s@, sub@)).last()@ == ran.last()@); | ||
res.push(strings[n]); | ||
assert(res@.last() == strings[n as int]); | ||
assert(res@.drop_last() == res_old@); | ||
// assert (ran_f == res@); | ||
// assert([email protected]() == strings[n as int]); | ||
// assert (strings[n as int] == [email protected](0, n as int + 1).last()); | ||
// assert (res_old == filtered_sub); | ||
// assert (strings[n as int] == [email protected](0, n as int + 1).filter (|s: &str| is_subseq_of(s@, sub@)).last()); | ||
// assert ([email protected](0, (n as int) + 1).filter (|s: &str| is_subseq_of(s@, sub@)) == [email protected](0, n as int).filter (|s: &str| is_subseq_of(s@, sub@)).push(strings[n as int])); | ||
// assert(strings[n as int]@ == [email protected](0, n + 1).filter(|s: &str| is_subseq_of(s@, sub@)).last()@); | ||
// assert([email protected]_last() == res_old); | ||
} | ||
} | ||
assert(strings@.subrange(0, strings@.len() as int) == strings@); | ||
// assert ([email protected](0, n as int).filter (|s: &str| is_subseq_of(s@, sub@)) == res@); | ||
res | ||
} | ||
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