so my function 'flatten' is to take a list of characters and digits to a string

flatten :: [(Char, Int)] -> String
flatten [] = []
flatten [(x,y):xs)] = x:(show y    flatten xs)

but I keep getting parse error, can anyone help me understand? Thanks.

 parse error (possibly incorrect indentation or mismatched brackets)
   |
18 | flatten :: [(Char, Int)] -> String
   | ^

CodePudding user response：

The compile error likely originates from something before the flatten function, for example you forgot to close a bracket.

As for the flatten function itself, for the second clause you should not use square brackets, otherwise you define a pattern of a list of lists of 2-tuples. You thus use (x, y):xs) as pattern:

flatten :: [(Char, Int)] -> String
flatten [] = []
flatten ((x,y):xs) = x : show y    flatten xs

CodePudding user response：

flatten [(x,y):xs)] = x:(show y    flatten xs)
                 ^