[Freeciv-Dev] Re: (PR#12873) OR Requirements for Buildings

["Benoit Hudson" <bh@xxxxxxxxxxxxxxxxxxx>]

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=12873 >

On Sat, Apr 23, 2005 at 09:54:31AM -0700, Jason Short wrote:
> Vasco Alexandre da Silva Costa wrote:
> > So an answer is: Reverse Polish Notation aka postfix notation. Like this:
> > sreqs    =
> >     { "type", "name", "range"
> >       "Tech", "Electronics", "Player"
> >       "Building", "Factory", "City"
> >       "Operator", "AND"

> Not that I'm in favor of such craziness but prefix notation would be
> better.  Just reverse the above list and you have prefix notation.

This seems like a good idea; now we can have a single effect that
describes how a hydro/power/nuclear/hoover increases production rather
than the current error-prone cut & paste technique, and this also makes
it more elegant to state that bonuses don't stack.

I'm not sure why it needs to be "Operator", "AND" rather than just a
single line with the bare-word 'and.'

We could have this just be 'reqs' and give it a NOT operator.

More ambitiously, a syntax I could see:
        reqs := "reqs = {" reqlist "}"
        reqlist := reqitem reqlist | reqitem
        reqitem := requirement | reqoperator
        reqoperator := '(' | ')' | 'and' | 'not' | 'or'
        requirement := ...
then we can do:
 reqs = { "type", "name", "range"
           and {
              "Tech", "Electronics", "Player"
              "Building", "Factory", "City"
              or {
                "Terrain", "Mountains", "Adjacent"
                "Special", "River", "Adjacent"
              }
              not "Terrain", "Ocean", "Adjacent"
           }
        }
which means we need electronics and a factory and be near either
mountains or river but not be on the coast (that last one just to show
the 'not' operator).

It's not unlikely that we should just use yacc (or bison) to parse this.

        -- Benoît