OpenEuphoria

Re: Parsing a Dice Roll String

• Posted by Matt Lewis <matthewwalkerlewis at yahoo.com> Aug 05, 2004
• 454 views

Christian Cuvier wrote:
> 
> > Subject: Parsing a Dice Roll String
> > 
> > 
> > posted by: cklester <cklester at yahoo.com>
> > 
> > I'm writing a die roller and need to be
> > able to parse a dice function string.
> > 
> > Some examples:
> > 
> >    3d6+5 (roll 6-sided die 3 times, add 5 to sum)
> >    4d6-Lowest (roll 6-sided die 4 times, discard lowest die)
> >    4d6-Highest (roll 6-sided die 4 times, discard highest die)
> >    2d10*3-3d4 (roll 10-sided die twice, multiply by 3, then subtract
> >                the result of rolling a 4-sided die three times)
> >    5d12/10 (roll 12-sided die five times, divide result by 10)
> > 
> 
> Well, I'd expect Matt's matheval.e to be able to handle this with minor text 
> translation.
> My understanding of your pb is: parse a string like `
> roll ::=
> ({<number>d<sides>[<operation>(roll | <reference> |
> <constant>])[<operation>])+
> 
> where <reference is any of "Lowest" or "Highest" (any more?).
> What's to be stored in list_Rolls? The roll outcome?
> <number> and <sides> are positive integers, <constant> is an atom..
> <operation> is any of +-*/ (any more?)
> Did I get it?

It would sort of work.  If you put these types of things through matheval, 
here's what you'd get:

3d6+5:  { POLYNOMIAL, "D6", {5,3}}
4d6-lowest:  { ADD, { VAR, "D6", 4 }, { VAR, "LOWEST", {-1} }}
2d10*3-3d4:  { ADD, { VAR, "D10",{6}},{ VAR,"D4",{-3}}}

One problem is that matheval tries to simplify things if it can, so 2d10*3
looks like 6d10 to it, even though that's not correct.  Also, it tries hard
to make things into polynomials if possible, since that's a lot more 
compact, and also faster to evaluate.

If you took out the call_func( SIMPLIFY, {expr[1]}) call at the end of
Parse() in parseval.e, you might be able to avoid some of these things.

Matt Lewis