-- http://i...content-available-to-author-only...e.com/sZ9tiN
import Data.List
import Data.Maybe
checkBraces "" = True
checkBraces e = checkBrace e [] where
	openBraces = "({["
	closeBraces = ")}]"
	braceToBrace fromBraces toBraces brace = toBraces!!(fromJust $ elemIndex brace fromBraces)
	otcBrace = braceToBrace openBraces closeBraces
	checkBrace (c:e) s | elem c openBraces = checkBrace e ((otcBrace c):s)
	checkBrace (c:e) (h:s) | (elem c closeBraces) && (h==c) = checkBrace e s
	checkBrace (_:e) _ = False
	checkBrace [] [] = True
	checkBrace [] _ = False
main = mapM_ (print . checkBraces) bracesExpressionExamples where
	bracesExpressionExamples = 
		[
			"({[{}]{}[]})",
			"({}}{[{}]{}[]})",
			"({[{}]{}[]}",
			"({[{}]{}]})",
			"({[{}{}[]})",
			"",
			"{}"
		]