Re: Lisp history: IF, etc.

Kaz Kylheku <643-408-1753@kylheku.com> writes:

   On 2024-04-03, Alan Bawden <alan@csail.mit.edu> wrote:
   > Lisp doesn't really have statements _because_ McCarthy invented the
   > conditional expression.  That's kind of the point.  Other programming
   > languages at the time (e.g. FORTRAN and ALGOL) only had conditional
   > statements.  McCarthy invented the conditional expression and thus
   > created the first expression-only programming language.

   However, conditional expressions ultimately come from math. E.g for
   specifying a discontinuous function:

      f(x) = { x, if x >= 0
             { 0, if x < 0

   If you think about it, it's actually kind of ignorant to invent a
   programming language with imperative if statements, but in which where
   the math conditional is missing.

If you think like a historian, you don't describe this as "ignorant".
It's just not something that was above the horizon in the mind set of
the time.  After all, that mathematical notation you are referring to
isn't something that mathematicians get very formal about.  It has a
status that's midway between being able to define something using a
simple equation, and having to resort to a definition in the form of a
paragraph of words.  Realizing that you could tighten that notation up
and use it in a programming language _as a kind of expression_ is
actually a bit of a leap.

   > People sometimes sloppily say that "McCarthy invented the
   > if-expression", by which they really mean just (1).  It is also true

   That could be the origin of the misconception; someone is going to
   take that sort of statement literally.

Yes, that was exactly my point.

- Alan