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|| Part 1


decode_hex_string []           = []
decode_hex_string ('+':xs)     = ' ': decode_hex_string xs
decode_hex_string ('%':x:y:xs) = c  : decode_hex_string xs
                                 where c = (decode (a + b))
                                       a = (hex_num x) * 16
                                       b = (hex_num y)
decode_hex_string ('%':xs)     = error "No hex number to decode."            
decode_hex_string (x:xs)       = x  : decode_hex_string xs

|| Gives the decimal value of a hexidecimal number
hex_num x = numval [x], if (digit x)
hex_num x = f, if (x >= 'a') 
            where
            f  = ((code x) - (code 'a')) + 10, if (x <= 'f')
hex_num x = f, if (x >= 'A') 	         		    
            where
	    f  = ((code x) - (code 'A')) + 10, if (x <= 'F')

		
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|| Part 2

paren ::= LP num | RP num

|| tokenize_parens :: [char]->[paren]
|| tokenize_parens "()[/*()[]*/]" 
||                    => [LP 1,RP 1,LP 2,LP 3,LP 1,RP 1,LP 2,RP 2,RP 3,RP 2]

tokenize_parens ('(':rest)     = LP 1 : tokenize_parens rest
tokenize_parens (')':rest)     = RP 1 : tokenize_parens rest
tokenize_parens ('[':rest)     = LP 2 : tokenize_parens rest
tokenize_parens (']':rest)     = RP 2 : tokenize_parens rest
tokenize_parens ('/':'*':rest) = LP 3 : tokenize_parens rest
tokenize_parens ('*':'/':rest) = RP 3 : tokenize_parens rest
tokenize_parens [] = []
tokenize_parens else = error "bad paren"

	    
|| balanced (tokenize_parens "()[/*()[]*/]") 
||                    => True    
balanced = bsr []
	   where bsr [] [] = True                             || done. 
	         bsr (RP x:LP x:stack) list = bsr stack list  || reduce.
                 bsr stack [] = False                         || error.
                 bsr stack (p:list) = bsr (p:stack) list      || shift.

|| variation of balance that reduces as it shifts	    
balanced2 = helper []
	    where helper [] [] = True
                  helper x [] = False
                  helper x (LP num:ys) = helper (LP num:x) ys
                  helper (LP num:xs) (RP num:ys) = helper xs ys