Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I stumbled across Dice::Simple and RPG::Dice in the code section, and it reminded me of a Pascal program I wrote back in the early '90s for a class. A typical calculator assignment, that I later tweaked for RPG use. I'd love to port it to Perl, but because of the syntax I can't cheat and use eval() like the aforementioned modules. Attached is the help doc as well as a few run examples. Should I change the syntax, or what's a good starting point other than brute-force character-by-character parsing as I did originally? 
Help Doc:
----------------------------
Key:
n = number (integers only)
l = list (of anything)
ln = list of numbers
exp = expression (i.e. any valid expression)

Operators:
+,-,/,*     Integer math only
d           ex. n1dn2 = Roll a n2 sided die n1 times and
            sum the results.
@[]         ex. n@[expr] = evaluate expr n times and put 
            the results in a list.
<,>         Selectors.  ex. n1>ln = select the greatest
            n1 items from the list ln.
&           ex. &ln = sum the numbers in the list ln.

Default order of prececence, highest to lowest:
()'s
d
*,/
+,-
@
>,<
&

Examples:  3d6        ! Returns a value 3 to 18.
           (1d4)d20   ! Rolls a 20 sided die 1 to 4 times
                        and sums the results.
           6@[3d6]    ! Returns 6 values of 3 to 18 in a
                        list.
           6>12@[3d6] ! Returns the best 6 of 12 3d6's in
                        a list.
           6@[&3>4@[(1d5)+1]] ! Equivelant to the ol'
                        "Roll 6 stats -- 4d6, re-roll
                        1's, drop the lowest die."

Note that n1dn2 is logically equivelant to &n1@[1dn2]
----------------------------
Sample output:
----------------------------
Command: 3d6
Value: 9
Command: 3d6
Value: 10
Command: 6@[3d6]
 ( 14 13 11 13 9 13)
Command: 6@[3d6]
 ( 7 11 15 17 7 7)
Command: 6@[&3>4@[(1d5)+1]]
 ( 14 12 15 12 10 11)
Command: 6@[&3>4@[(1d5)+1]]
 ( 16 15 12 14 16 14)
Command: 4@[6@[3d6]]
 (
  ( 13 8 6 9 4 12)
  ( 13 7 9 10 11 9)
  ( 9 12 10 9 13 13)
  ( 10 8 9 7 7 12)
 )
Command: X = 3d6
Symbol "X" created.
Value: 0
Command: 4@[X]
 ( 10 12 14 9)
Command: X<20@[X]
 ( 6 7 7 7 8 9 9 10 10 10 11 11 11 12 12)
Command: X<20@[X]
 ( 4 5 7 7)
----------------------------

[download]

Replies are listed 'Best First'.
Re: Dice calcs?
by BigLug (Chaplain) on Sep 18, 2002 at 03:27 UTC
    OK. I've taken a look at this and there's are a problem with your order of preference: @[] has to be at the top otherwise 6@[3d8] will roll an 8 sided dice three times and return that value six times. Thus you'll get something like {6, 6, 6}. With the @[] at the top it will run 3d6 three times and you'll get three different values.

    Below is an example of a dice calculator using your given rules. There are no symbol defs though and its not interactive. There's also a lot of code in there for verbose output. You might want to can it by setting $verbose=0 :)

    You'll notice I've changed the precedence to (), @, <>, &, d, *, /, +, - in order to get your examples to work.

    Read more... (5 kB)
[reply]
[d/l]
      Hmmmm.... I hadn't thought about in-place substitutions. My original assignment was an infix-to-postfix calculator, and the precedence order I listed was required for that algorithm to work.

      I did find a few bugs in your solution. I realize your code was just an example, and I appreciate the insight, I just want to make sure anyone that downloads it realizes there are issues. For example, your code wouldn't allow for multiple @[] operators at the same level (i.e. &3>4@[1d6]+&1>4@[1d100]). Division should be integer. Negative numbers (and thus unary -) need to be implemented. There's no general syntax checking.

      I went ahead with the in-place substitution idea and should have some code ready to post soon. I've addressed all of the above issues and a few more. There are still issues with precedence lists, though.... with this method it is impossible/difficult for operators to share the same precedence. For example, normally something like 5*20/3*3 should equal 99, but in this case it comes up 11 (100/9). That's not a problem as long as it's documented.

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        Oh, good bug-find. Here's a couple of fixes that you've prolly already done

        1. To get it to do the multiple @ operators at the same level you need to 

        use Regexp::Common

        [download]
        Then replace the 'Precedence 5' regexp with: 
        $term=~s/(\d+)@($RE{balanced}{-parens=>'[]'})/rpt($1,$2)/eg;

        [download]

        2.To get it to do the * and / from left to right, change 'Precedence 3' to this single regexp: 

        $term=~s/(\d+)([\*\/])(\d+)/int(eval("$1$2$3"))/eg;

        [download]
        and change 'Precedence 4' to 
        $term=~s/(\d+)([+-])(\d+)/eval("$1$2$3")/eg;

        [download]

        Hope these help you with your efforts. There is still no syntax checking but I figure you can handle stopping people from putting 3*+/4. Oh, and you probably want to handle negative numbers before 'Precedence 4'

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[d/l]
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