Make an application that displays text at random that conforms to the specified regex

Question

OK, so in the spirit of Code-Golf, I\'m trying out something new here: Code-Bowling.

In golf, you try to get the lowest score (smallest application, mos

Answer 1

The asker mentioned regular expressions, so clearly he is looking for an answer using regular expressions. I was baffled after I saw that most of the answers thus far totally fail to realize the power of regular expressions and embrace them.

Thus, my solution. Python code that generates random matches given a regular expression. And the output is totally random, I swear!

import random, time

def parse_regex(regex):
        path = [('()', []), ('|', [])]
        path[0][1].append(path[1])
        i = 0
        while i < len(regex):
                char = regex[i]
                if path[-1][0] in ('[]', '[^]'):
                        if char == ']' and path[-1][1]:
                                old2 = path.pop()
                                assert old2[0] in ('[]', '[^]')
                        elif char == '-' and len(path[-1][1]) and i+1 < len(regex) and regex[i+1] != ']':
                                tmp1 = path[-1][1].pop()
                                assert tmp1[0] is None
                                tmp1 = tmp1[1]
                                tmp2 = regex[i+1]
                                assert ord(tmp2) > ord(tmp1)
                                for tmp in range(ord(tmp1), ord(tmp2) + 1):
                                        path[-1][1].append((None, chr(tmp)))
                                i += 1
                        else:
                                path[-1][1].append((None, char))
                else:
                        if char == '(':
                                new1 = ('()', [])
                                new2 = ('|', [])
                                new1[1].append(new2)
                                path[-1][1].append(new1)
                                path.extend([new1, new2])
                        elif char == ')':
                                old2 = path.pop()
                                old1 = path.pop()
                                assert old2[0] == '|'
                                assert old1[0] == '()'
                        elif char == '|':
                                new2 = ('|', [])
                                old2 = path.pop()
                                assert old2[0] == '|'
                                path[-1][1].append(new2)
                                path.append(new2)
                        elif char == '[':
                                tmp = '[]'
                                if i+1 < len(regex) and regex[i+1] == '^':
                                        tmp = '[^]'
                                        i += 1
                                new = (tmp, [])
                                path[-1][1].append(new)
                                path.append(new)
                        elif char == '.':
                                path[-1][1].append(('.', None))
                        elif char in ('*', '+', '?'):
                                assert len(path[-1][1])
                                tmp = path[-1][1].pop()
                                path[-1][1].append((char, tmp))
                        else:
                                path[-1][1].append((None, char))
                i += 1
        assert len(path) == 2
        return path[0]

def generate_match(regextree):
        match = ''
        if regextree[0] == '()':
                regextree = random.choice(regextree[1])
                match += generate_match(regextree)
        elif regextree[0] == '|':
                for item in regextree[1]:
                        match += generate_match(item)
        elif regextree[0] == None:
                match += regextree[1]
        elif regextree[0] == '.':
                match += random.choice([chr(i) for i in range(32, 127)])
        elif regextree[0] in ('*', '+'):
                if regextree[0] == '+':
                        match += generate_match(regextree[1])
                # We favour shorter matches
                while True:
                        if random.choice(['yes', 'yes', 'no']) == 'yes':
                                match += generate_match(regextree[1])
                        else:
                                break
        elif regextree[0] == '?':
                if random.choice(['yes', 'no']) == 'yes':
                        match += generate_match(regextree[1])
        elif regextree[0] == '[]':
                match += random.choice([generate_match(item) for item in regextree[1]])
        elif regextree[0] == '[^]':
                match += random.choice(list(set(chr(i) for i in range(32, 127)) - set(generate_match(item) for item in regextree[1])))
        else:
                raise
        return match

t1 = time.time()
y, m, d = time.localtime(t1)[:3]
t2 = time.mktime((y, m, d, 0, 0, 0) + time.localtime(t1)[-3:])
t = int(t1 - t2)

# Can't rely on python setting the random seed randomly enough.
# Thus, we seed it with the help of cafebabe and current time.    
random.seed((0xcafebabe ^ 0x4eb) + t / 21600)

print generate_match(parse_regex('Good (Morning|Afternoon|Evening|Night)'))