I've written a function that is supposed to add parenthesis to sin/cos expressions.

For example

•  Sin5+3        ->    Sin(5) + 3
• SinCos(5+3)   ->    Sin(Cos(5+3))
• SinCos5 * 3   ->    Sin(Cos(5)) * 3
  

The problem is that it converts the following expression
SinSin(5+1+2)
into
Sin(Sin(5)+1+2)

Could someone point me to the direction of a solution to this? Thanks in advance!

convert :: String -> String                                                 
convert s = convert' s 0                                                    
                                                                            
convert' :: String -> Int -> String                                         
convert' [] n                                                         = replicate n ')'
convert' (a:as) n | ((a == 'n' || a == 's') && ((take 1 as) /= "("))  = a : "(" ++ (convert' as (n+1))
                 | ((a == '+' || a == '*') && (n > 0))               = (replicate n ')') ++ [a] ++ (convert' as 0)
                 | otherwise                                         = a : (convert' as n)