d20 die rolling string parser

[ednark]

ok here is one for you

a d20 math parser...

in roleplaying games based on dice rolling you run across statements like

1d20+(1d6*4)

mean roll a 20 sided die rand(1,20), add it to ( a 6 sided die rand(1,6) multiplied by 4 )

the d is really just and new operator meaning rand(1,RIGHT) repeated LEFT times

i would like to take the a string like above, and have php evaluate this into a single integer...

but im not really sure how to get started on making a string parser in in php

anyone done one before...

my initial thought was to step char by char through using $string{$x} looking for parens, kina like a sax xml parser, and build a tree of the statement then evaluate each node starting with the leaves up.

is there a quicker way anyone has seen using native php functions

[majik-sheff]

Hehe, interesting challenge. I'd be interested to see how others did it, but here's my stab at a solution (14 lines):

function parse_dice($dice) {
		$dice = strtolower($dice);
		$dice = preg_replace_callback("/[0-9]+d[0-9]+/", "parse_dice_callback", $dice);
		$dice = "\$result = $dice;";
		eval($dice);
		return($result);
	}

function parse_dice_callback($input) {
	$pieces = explode("d", $input[0]);
	$rollTotal = 0;
	for($j = 1; $j <= $pieces[0]; $j++) {
		$rollTotal += rand(1, $pieces[1]);
	}
	return($rollTotal);
}

just feed parse_dice your string and it'll spit back a number

[ednark]

oooooo i like it, i didn't even know about the preg_replace_callback function, that one must have slipped by me...

here is the version i whipped up based mostly on your code, and one other person in the d20-xml yahoo group

<?php
#
# allows:
#  operators: ^ * % / + - d
#     parens: ()
#  functions: ceil() floor()
#

$remember_collapse = NULL;

function evalDiceRoll ( $roll_string )
{
    /// remove any spaces, and lowercase everything
    $prepared_string = str_replace(' ','',strtolower($roll_string));
    /// if the string is not wellFormed
    if ( !wellFormedString($prepared_string) ) {
        /// report that the string is bad
        return 'invalid characters in string';
    }
    /// collapse all instances of xdy into whatever that roll happened to be
    /// allow slight variation of ( +xdy | xd+y | +xd+y )
    /// find each instance of the regular expression, pass it to parseDiceCallback() and replace it with the result
    $collapsed_string = preg_replace_callback('/\+?\d*d\+?\d*/','parseDiceCallback',$prepared_string);
    /// not part of algorithm: bring in a global variable so that we can print out what the collapsed string was later
    global $remember_collapse;
    $remember_collapse = $collapsed_string;
    /// actually do the eval of the string, suppress any errrors this eval may throw
    $evaled_string = @eval("return($collapsed_string);");
    /// return either the valid result or a result message
    return $evaled_string===false ? 'invalid d20 format' : $evaled_string;
}

function wellFormedString( $roll_string )
{
    /// find only these combinations of characters from beginning to end, anything else found means bad string
    return preg_match('/^([\d\/\*\^\+\-\%\(\)d]|floor|ceil)+$/',$roll_string) ? true : false;
}

function parseDiceCallback ( $prepared_string )
{
    /// get left and right of xdy
    list( $left, $right ) = explode('d',$prepared_string[0]);
    /// if left or right is 0 or does not exist, then say total is 0
    if ( $left<=0 || $right<=0 ) { return 0; }
    /// start the total at 0
    $roll_total = 0;
    /// do once for everytime specified in the left
    foreach ( range(1,$left) as $roll_number ) {
        /// do a random roll
        $roll_total += mt_rand(1,$right);
    }
    /// return the results
    return($roll_total);
}

$roll = isset($_POST['roll']) ? $_POST['roll'] : '1d6+2' ;
$result =  evalDiceRoll($roll);

print <<<END_OF_FORM

<form action="{$PHP_SELF}" method="post">
<table><tr>
  <td align="right">Roll :</td><td><input style="text-align: center;" name="roll" value="{$roll}" type="text" size="20"></td>
 </tr><tr>
  <td align="right">Collapses To :</td><td>{$remember_collapse}</td>
 </tr><tr>
  <td align="right">Result :</td><td>{$result}</td>
</tr></table>
<input type="submit" name="Calculate This Roll">
</form>

END_OF_FORM;

?>

[majik-sheff]

Tee-hee

Here it is in 9 lines, complete with cleanup and error checking. 🙂

    function dice($diceString)
    {
        $cleanString = strtolower(preg_replace('/\s+/', '', $diceString));
        if (preg_match('/^([\d\/\*\^\+\-\%\(\)d]|floor|ceil)+$/', $cleanString) == 1) {
            $expandedDiceString = preg_replace('/(\d+)d(\d+)/e', "'(' . str_repeat('mt_rand(1, \\2)+', \\1) . '0)'", $cleanString);
            return(@eval("return($expandedDiceString);"));
        }
        return(FALSE);
    }