Like many others here I once wrote a toy lisp in golang, and I added a help function. It would give usage-information for all the built-in functions.

      > (help +)
      Arguments N arg1..argN
      Adds all arguments present to the first number.

      > (help map)
      Arguments lst:list fun:function
      Return a list with the contents of evaluating the given function on every item of the supplied list.
      See-also: map-pairs