Specification entailments

NOT YET SUPPORTED: This feature is not yet supported in Prusti. See PR #138 for the status of this feature as well as a prototype. The syntax described here is subject to change.

The contract for a closure or function pointer variable can be given using the specification entailment syntax:

use prusti_contracts::*;

  f |= |a: i32, b: i32| [
    requires(a == 5),
    requires(b == 4),
    ensures(result > 4)
fn example<F: Fn (i32, i32) -> i32> (f: F) { ... }

In the above example, f, the argument to example, must be a function that takes two i32 arguments. A call to f inside the body of example is only valid if the preconditions are satisfied, and the result of that call must satisfy the postcondition given.


  • arrow syntax (~~>)
  • ghost arguments
  • history invariants
  • multiple-call specification entailment