Question

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What does # mean in LISP

I am learning lisp, but one thing I do not understand is why it is necessary for #’ to be used. If a function with a specific name exists, why would lisp think its a variable?
Ex:

>(remove-if-not #'evenp '(1 2 3 4 5 6 7 8 9 10))
 (2 4 6 8 10)

Answer 1

Some lisps, like Common Lisp, require this. Others, like Scheme, do not.

You need to do this because the Lisp you’re using has a separate namespace for functions versus “normal” variables. If you left out the #' then the symbol evenp would be interpreted as referring to the “normal” (non-function) namespace.