CODEWITHSUNDEEP
haskell
Luca9984
Luca9984

Reputation: 151

Accessing attributes of a datatype

I created a new datatype:

data Human = Human [Names] Age
  deriving(Eq,Show)
type Names = String
type Age = Int

And now I want to access the elements of [Names] for an object of type Human:

human1 = Human ["FirstName","LastName"] 22

Is there a simple way to do this for my example such as Names human1 ?

Upvotes: 0

Views: 78

Answers (2)

Igor Drozdov
Igor Drozdov

Reputation: 15045

In this case the simplest way is to define a function, which pattern-matches the Human data type:

getNames (Human names _) = names

Otherwise, you can use Record Syntax to define fields of the record:

data Human = Human { names :: [Names], age :: Age }

Using this syntax you achieve names and age functions, which allow you to access the fields:

human1 = Human ["FirstName","LastName"] 22
names human1

Upvotes: 5

Vora
Vora

Reputation: 301

You can either make your own accessors

names :: Human -> [Names]
names (Human n _) = n

or use lenses, which gives you that and much more.
http://hackage.haskell.org/package/lens-tutorial-1.0.3/docs/Control-Lens-Tutorial.html

Upvotes: 4

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