error[E0277]: expected a `std::ops::FnOnce<()>` closure, found `{integer}`
  --> $DIR/closure-expected.rs:3:15
   |
LL |     let y = x.or_else(4);
   |               ^^^^^^^ expected an `FnOnce<()>` closure, found `{integer}`
   |
   = help: the trait `std::ops::FnOnce<()>` is not implemented for `{integer}`
   = note: wrap the `{integer}` in a closure with no arguments: `|| { /* code */ }

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.