Re: Integral types and own type definitions (was Re: Suggested method for returning a string from a C program?)

On 2025-03-31, Alan Mackenzie <acm@muc.de> wrote:

Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
>
[ .... ]
>

I don't know of any language that uses "-" for both negation (prefix,
one operand) and subtraction (infix, two operands) and treats -5
as a single token rather than a unary minus operator applied to the
constant/literal "5".

>
How about Lisp?  The unary operator is (- 5), the binary (- 10 5).
>
It doesn't match your second parenthetical remark ("infix") but
otherwise it does.

Lisp could be infix if we want with some macro:

 (infix-environment
   ... (10 - (a * 3)) ...)

Here, the fictional macro infix-environment implements a code walker of
its interior looking for situations where the second place of a form is
a symbol with a function binding, and the first place isn't a symbol, or
not one with a function binding.  Those expressions are then treated by
a conversion of (x1 x2 x3 ...) to (infix x1 x2 x3). When the conversion
is complete, the infix-environment macro removes itself, or rewrites
itself to progn.  The (also fictitious) infix macro then expands the
infixes, turning (infix 10 - (a * 3)) into (- 10 (* a 3)).

Things like (a cons (b cons c)) would also work for (cons a (cons b c)),
not only math infix. However, the infix macro could recognize
infix without parentheses, using operator precedence.

So then we would have a language in which we have - A unary,
A - B infix, and -5 is a negative constant.


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