Macro fallible 

macro_rules! fallible {
    ($base:expr) => { ... };
    ($base:expr, $($b_type:ty :)? | $id:ident $(: $ty:ty)? | $expr:expr $(, $($tail:tt)+)? ) => { ... };
    ($base:expr, $($b_type:ty :)? move | $id:ident $(: $ty:ty)? | $expr:expr $(, $($tail:tt)+)? ) => { ... };
    ($base:expr, no_discard $($b_type:ty :)? | $id:ident $(: $ty:ty)? | $expr:expr $(, $($tail:tt)+)? ) => { ... };
    ($base:expr, no_discard $($b_type:ty :)? move | $id:ident $(: $ty:ty)? | $expr:expr $(, $($tail:tt)+)? ) => { ... };
}

A macro used to reduce boilerplate when nesting multiple calls to process or process_no_discard inside each other.

Fallible and IterResult must be imported to use the macro.