repeat

How would one write a regex that matches a pattern that can contain quotes, but if it does, must have matching quotes at the beginning and end? "?(pattern)"? Will not work because it will allow patterns that begin with a quote but don't end with one. "(pattern)"|(pattern) Will work, but is repetitive. Is there a better way to do that without repeating the pattern? You can get a solution without repeating by making use of backreferences and conditionals : /^(")?(pattern)(?(1)\1|)$/ Matches: pattern "pattern" Doesn't match: "pattern pattern" This pattern is somewhat complex, however. It first

How to match any character which repeats n times? Example: for input: abcdbcdcdd for n=1: .......... for n=2: ......... for n=3: .. ..... for n=4: . . .. for n=5: no matches After several hours my best is this expression (\w)(?=(?:.*\1){n-1,}) //where n is variable which uses lookahead. However the problem with this expression is this: for input: abcdbcdcdd for n=1 .......... for n=2 ... .. . for n=3 .. . for n=4 . for n=5 no matches As you can see, when lookahead matches for a character, let's look for n=4 line, d 's lookahead assertion satisfied and first d matched by regex. But remaining d

I want to repeatedly apply a function simplify' until the result is "stable" (i.e. simplify'(x) == x ): simplify :: Expr -> Expr simplify expr = let iterations = iterate simplify' expr neighbours = zip iterations (tail iterations) simplified = takeWhile (\(a, b) -> a /= b) neighbours in snd $ last ((expr, expr) : simplified) simplify' :: Expr -> Expr This seems to be a common problem to me. Is there a more elegant solution? Update: I found a much simpler solution, but I'm still looking for a more elegant solution :) simplify expr = let next = simplify' expr in if next == expr then expr else

In Python, if I do this: print "4" * 4 I get > "4444" In Perl, I'd get > 16 Is there an easy way to do the former in Perl? Vinko Vrsalovic $ perl -e 'print "4"x4; print "\n"' 4444 The x operator is documented in perldoc perlop . Here binary means an operator taking two arguments, not composed of bits, by the way. Binary "x" is the repetition operator. In scalar context or if the left operand is not enclosed in parentheses, it returns a string consisting of the left operand repeated the number of times specified by the right operand. In list context, if the left operand is enclosed in

I try to match/get all repetitions in a string. This is what I've done so far: var str = 'abcabc123123'; var REPEATED_CHARS_REGEX = /(.).*\1/gi; console.log( str.match(REPEATED_CHARS_REGEX) ); // => ['abca', '1231'] As you can see the matching result is ['abca', '1231'] , but I excpect to get ['abc', '123'] . Any ideas to accomplish that? 2nd question: Another thing I excpect, is to make it possible to change the duration how often a char needs to be in the string to get matched... For example if the string is abcabcabc and the repetation-time is set to 2 it should result in ['abcabc'] . If