Macro thruster::middleware

macro_rules! middleware {
    [ @ tailtype $ ctx : ty => $ head : expr ] => { ... };
    [
@ tailtype $ ctx : ty => $ head : expr , $ ( $ tail_t : ty => $ tail_e : expr
) , + ] => { ... };
    [
@ internal $ ctx : ty => $ head : expr , $ ender : expr ] => { ... };
    [
@ internal $ ctx : ty => $ head : expr , $ ( $ tail_t : ty => $ tail_e : expr
) , + , $ ender : expr ] => { ... };
    [
$ ctx : ty => $ head : expr ] => { ... };
    [
$ ctx : ty => $ head : expr , $ ( $ tail_t : ty => $ tail_e : expr ) , + ] => { ... };
}

The middleware macro takes a series of functions whose contexts all have into implemented, and then links them together to run in series. The result of this macro is a single MiddlewareChain.