// Fundamental list manipulation functions. Part of the standard library.
// first, rest, cat

[
    0 get@
] 'first def

[
    #t (f) // True only for the first element
    [] (n) // New list
    [
        [$f] [
            #f (f)  // Set flag to false
            drop    // Discard first element
        ] [
            $n -> (n)
        ] ifelse
    ] foreach
    $n
] 'rest def