Or Forth.

http://www.yosefk.com/blog/my-history-with-forth-stack-machi...

my mind was immediately blown away by the following passage right at the top of system.fth, the part of pForth implemented in Forth on top of the C interpreter:

    : (   41 word drop ; immediate
    ( That was the definition for the comment word. )
    ( Now we can add comments to what we are doing! )