() => {} Is actually:() => Expression Rule: ref|opt ParameterWithMemberAttributes => AssignExpression https://dlang.org/spec/expression.html#lambdas
This would mean, that this one should work as well. And you can![1] I have changed line 13 from `F();` to `return F();`. Why does this help??? This is a little weird. [1]: https://run.dlang.io/is/eGah5v
