Evaluate dice rolling notation strings

Question

Rules

Write a function that accepts string as a parameter, returning evaluated value of expression in dice notation, including addition and multiplication.

To

Answer 1

Python, 452 bytes in the compressed version

I'm not sure if this is cool, ugly, or plain stupid, but it was fun writing it.

What we do is as follows: We use regexes (which is usually not the right tool for this kind of thing) to convert the dice notation string into a list of commands in a small, stack-based language. This language has four commands:

• mul multiplies the top two numbers on the stack and pushes the result
• add adds the top two numbers on the stack and pushes the result
• roll pops the dice size from the stack, then the count, rolls a size-sided dice count times and pushes the result
• a number just pushes itself onto the stack

This command list is then evaluated.

import re, random

def dice_eval(s):
    s = s.replace(" ","")
    s = re.sub(r"(\d+|[d+*])",r"\1 ",s) #seperate tokens by spaces
    s = re.sub(r"(^|[+*] )d",r"\g<1>1 d",s) #e.g. change d 6 to 1 d 6
    while "*" in s:
        s = re.sub(r"([^+]+) \* ([^+]+)",r"\1 \2mul ",s,1)
    while "+" in s:
        s = re.sub(r"(.+) \+ (.+)",r"\1 \2add ",s,1)
    s = re.sub(r"d (\d+) ",r"\1 roll ",s)

    stack = []

    for token in s.split():
        if token == "mul":
            stack.append(stack.pop() * stack.pop())
        elif token == "add":
            stack.append(stack.pop() + stack.pop())
        elif token == "roll":
            v = 0
            dice = stack.pop()
            for i in xrange(stack.pop()):
                v += random.randint(1,dice)
            stack.append(v)
        elif token.isdigit():
            stack.append(int(token))
        else:
            raise ValueError

    assert len(stack) == 1

    return stack.pop() 

print dice_eval("2*d12+3d20*3+d6")

By the way (this was discussed in the question comments), this implementation will allow strings like "2d3d6", understanding this as "roll a d3 twice, then roll a d6 as many times as the result of the two rolls."

Also, although there is some error checking, it still expects a valid input. Passing "*4" for example will result in an infinite loop.

Here is the compressed version (not pretty):

import re, random
r=re.sub
def e(s):
 s=r(" ","",s)
 s=r(r"(\d+|[d+*])",r"\1 ",s)
 s=r(r"(^|[+*] )d",r"\g<1>1 d",s)
 while"*"in s:s=r(r"([^+]+) \* ([^+]+)",r"\1 \2M ",s)
 while"+"in s:s=r(r"(.+) \+ (.+)",r"\1 \2A ",s)
 s=r(r"d (\d+)",r"\1 R",s)
 t=[]
 a=t.append
 p=t.pop
 for k in s.split():
  if k=="M":a(p()*p())
  elif k=="A":a(p()+p())
  elif k=="R":
   v=0
   d=p()
   for i in [[]]*p():v+=random.randint(1,d)
   a(v)
  else:a(int(k))
 return p()