The type of a closure with a closure as its first argument cannot be written without parentheses

[ftxqxd]

The following code:

fn foo(x: ||u8|, u8|) {}

fails to parse, as the parser expects || to be a type of its own. Adding a space in between the |s does not help; one must write |(|u8|), u8| instead.

[kmcallister]

This syntax is gone.