a question about const and pure functions.

[Richard Kenner]

    A "const" call has no side-effects and its results depend purely on the
    values of its arguments.  This closely follows the mathematical notion
    of a "function".  A "pure" call has no side-effects, but in addition to
    it's arguments may depend upon the memory/global variables of the system.

"The devil is in the details", as they say!  Is memoization considered
a "side-effect", for example?  What about a function passed a pointer and
which indirectly modifies that point?  Is that a "side-effect"?  It's
very tricky to get definitions exactly right.