Pearlite

Pearlite is the language used in:

• contracts (ensures, requires, invariant, variant)
• proof_assert!
• the pearlite! macro

It can be seen as a pure, immutable fragment of Rust which has access to a few additional logical operations and connectives. In practice you have:

• Base Rust expressions: matching, function calls, let bindings, binary and unary operators, tuples, structs and enums, projections, primitive casts, and dereferencing
• Logical Expressions: quantifiers (forall and exists), logical implication ==>, logical equality a == b, labels
• Rust specific logical expressions: access to the final value of a mutable reference ^, access to the view of an object @

Logical implication

Since => is already a used token in Rust, we use ==> to mean implication:

proof_assert!(true ==> true);
proof_assert!(false ==> true);
proof_assert!(false ==> false);
// proof_assert!(true ==> false); // incorrect

Quantifiers

The logical quantifiers ∀ and ∃ are written forall and exists in Pearlite:

#[requires(forall<i: Int> i >= 0 && i < list@.len() ==> list@[i] == 0)]
fn requires_all_zeros(list: &[i32]) {
    // ...
}