CODEWITHSUNDEEP
haskell
Tymek
Tymek

Reputation: 3113

Define data type and use in function

How should I define tuple type Quartet, that will contain four elements – two Integrals and two Booleans, and functions firstTwo returning table of Integrals and secondTwo returning table of two Booleans?

data Quartet = Quartet (Int, Int, Bool, Bool)

--firstPair :: Quartet -> [Int, Int]
firstPair (a, b, _) = [a, b]

--secondPair :: Quartet -> [Bool, Bool]
secondPair (_, _, a, b) = [a, b]

Upvotes: 1

Views: 145

Answers (1)

ely
ely

Reputation: 77504

As you have defined it, the Quartet value constructor takes one argument, which is a 4-tuple. You could also define it like this:

data Quartet = Quartet Int Int Bool Bool

and it will work pretty much the same except the pattern matching will be slightly different.

You can also make a type synonym for 4-tuples of this particular type:

type Quartet = (Int, Int, Bool, Bool)

If you opt for this final approach, your functions will work just as you've written them, because pattern matching in this last case is nothing more than matching against a plain tuple.

However, if you use either of the first two cases, the key idea is that in your function definition, you have to pattern match the value constructor, so you need to include the Quartet value constructor as part of the pattern:

--firstPair :: Quartet -> [Int, Int]
firstPair (Quartet (a, b, _, _)) = [a, b]

--secondPair :: Quartet -> [Bool, Bool]
secondPair (Quartet (_, _, a, b)) = [a, b]

Upvotes: 3

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