Also same for Rebol & Red.

And its easy to view the source code from the console (REPL). Some examples from Rebol2...

    >> source func

    func: func [
        "Defines a user function with given spec and body."
        [catch]
        spec [block!] {Help string (opt) followed by arg words (and opt type and string)}
        body [block!] "The body block of the function"
    ][
        throw-on-error [make function! spec body]
    ]


    >> source source

    source: func [
        "Prints the source code for a word."
        'word [word!]
    ][
        prin join word ": "
        if not value? word [print "undefined" exit]
        either any [native? get word op? get word action? get word] [
            print ["native" mold third get word]
        ] [print mold get word]
    ]