[Vala] Contracts on lambdas

[Tristin Celestin <tristin_celestin yahoo com>]

Is it possible to write a lamba expression with a contract? This is
what I try to do now, and I get a compiler error.

Example:

delegate void strict_increment (int value);

...

int local_value = 0;
strict_increment = (value) requires (value > 0) => {
    local_value += value;
}