It's impossible to write a compose function with the declaration fn compose<T, F: Fn(T) -> T>(f1: F, f2: F) -> F As far as I'm aware the only way to write a

It's impossible to write a compose function with the declaration fn compose<T, F: Fn(T) -> T>(f1: F, f2: F) -> F As far as I'm aware the only way to write a function like that is fn compose<T, F: Fn(T) -> T>(f1: F, f2: F) -> F { f1 } and even then you can only call it like this let clos = |x| 2 * x; compose(clos, clos);