On 2021-04-02 16:55, Richard Damon wrote:
I think python only has 3 unary operations, + - and ~ and only + and -
can also be binary operations.
unary + has less uses, since it normally just passes its argument, if
valid, unchanged, but can be used to validate that its argument has the
right type. I am not sure if a type could define its own unary+ to do
something special, but I thought it could.
The Counter class from the collections module has a special use for unary +.
On 4/2/21 11:19 AM, John wrote:
True. It gets ambiguous when doing n*(-(x + y)) i.e. n x y + - *
(fail). The simplest solution is n 0 x y + - *
I can't actually think of any other unary operators.
On Fri, Apr 2, 2021 at 10:54 AM Richard Damon <rich...@damon-family.org> wrote:
One problem with trying to mix RPN with in-fix is that some operators,
like - can be either a unary or binary operation in the in-fix
notations, distinguished by context. In RPN you have lost that context.
is x y - - the same as -(x-y) or is it x-(-y) ? or is it waiting for
another operator and be x ?? (-(-y)) or is it expecting a previous
operand and is ?? - (x-y)
(same with +)
Typical RPN systems get around this by having unary - be a different
symbol/key that binary -
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