从数据类型Haskell返回值

Question

Lets say I have created the following Datatype that looks like this:

data MolSeq = DNA (String, String) String | Protein (String, String) String 

Then I create a MolSeq datatype of type DNA like this:

dna = DNA ("T2", "ACATAA") "DNA"

How can I then later in my program return let's say the value "T2"?

Thanks!

Answer 1

You can pattern match it, for example:

getMolString :: MolSeq -> String
getMolString (DNA     (s, _) _) = s
getMolString (Protein (s, _) _) = s

Here you have a live example

A data type is just data, you should make functions to work with that, you can't think of them as objects with attributes or methods.