Simple expression evaluator

Question

Hi all,
need some help with an expression evaluation:
user inputs a string like "x*x+dx*dy" or "x*dx-y*dy" and I
would like Flash to covert this to an actionscriptline so in the
code it appears like:
x=3;
dx=0.6;
dy=0.1;
aa=x*x+dx*dy;
trace(aa);
and the output would be: 9.06
Now my problem is converting the operator.
Anybody for a solution for this newbie?
thnx
Rob

Answer 1

Ok, so I think my advice stands then...
You could write your own expression parser, using eval("x")
when you came to parse an x in the string etc...and its probably
not too complicated to do if you're just dealing with
multiplication and addition.... or you could use existing code like
the example in the link I posted earlier to parse the expression
(I've used that code before for something more complex).
If you were writing your own parser you could use eval("x")
...but if it were me... I would do the opposite. That is to split
and join the string with the variable names, subsitituting their
values into the string and then run it through that expression
parser. Its basically just calculating a string version of a
numeric expression then with no variables.
For your variable --> value substitution (split and then
join) you need to do it in the order of the
dx and dy
then x and y
so you get it to work correctly.