Re: Precedence values for Reverse Polish

One thing to think about is the influence on your evaluator.
Specifically, if you have a stream like this:


n 0 >
                'ans' ans ans 1 - * :=
while




Then a straightforward evaluator would evaluate the (n 0 >) part long
before the while was seen. When the while came up, the stack would
look something like this:


true
11




What you might want to add is the notion of a deferred routine. HP48
calculators write this using << and >> characters. The above example
would be vaguely like this:


<< n 0 > >>
<< 'ans' ans ans 1 - * := >>
while




If you have this "deferred routine" thingie (I dunno what HP's call
them; I think of them as "lambdas" :)), then your RPN evaluator can
remain extremely simple.




Lex






"Nerd" <nerd@freeuk.com> writes:
> Also, I'd like to extend it to convert:
>
> if a = b then c := 1 else c := 2 to a b = c 1 := c 2 := if
>
> So "if" is a trinary operator. Or, since my language allows it:
>
> c := if a = b then 1 else 2 to c a b = 1 2 if :=

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