How to merge two functions into one in Haskell

Question

I want to merge two functions into one.

The functions are

 data Dice = Stone Char deriving (Show, Eq)

 calculateScore :: [Dobbelsteen]  -> Int
 calculateScore xs = sum[giveValueDice x | x <- xs]

 giveValueDice :: Dice -> Int
 giveValueDice (Stone d) = if d == 'W' then 5 else digitToInt d

Normally, I would just copy one line into the first function en change a little bit to make the syntax correct. But here I am kinda lost how to do this

Answer 1

As you've already noticed, you can't just directly inline here; the reason for this is that you're pattern matching on Stone in giveValueDice . This pattern matching can be moved inside the right side of the list comprehension:

 calculateScore :: [Dobbelsteen]  -> Int
 calculateScore xs = sum[if d == 'W' then 5 else digitToInt d | (Stone d) <- xs]

Another method for merging these two functions is using a where clause, which 'merges' one function into another while keeping them distince:

 calculateScore :: [Dobbelsteen]  -> Int
 calculateScore xs = sum[giveValueDice x | x <- xs]
   where
     giveValueDice :: Dice -> Int
     giveValueDice (Stone d) = if d == 'W' then 5 else digitToInt d