XO0172: function declaration without a body

Every fn declaration outside an interface needs a { ... } body. Only interface method signatures have no body. If the body is not written yet, use a typed hole ??? (core 3.7) so the rest of the program still checks. See core 3.2 and 15.

Example

fn f() -> Int
fn g() {}

Fix

fn f() -> Int { ??? }
fn g() {}

Run xo explain XO0172 for this text in a terminal, or see section 10.6 of the specification.