ん？ そこは数少ない「訳わかる」ところじゃないのか？
関数定義のシンタックスが書いてあるだけだぞ。

annotation: meta-annotation on function, currently used as documentation. Optional.
identifier: name of function. Required.
args: comma-delimited list of parameter names. Optional.
guards: guarding statement that act as a prerequisite for the function. Optional.
{ }: scoped block as function body. Required.