CODEWITHSUNDEEP
haskellfunctional-programming
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Reputation: 443

Interfaces in functional programming

In java and c# we have interfaces, what is the equivalent to that in a language like haskell or what is the concept called in functional programming?

Upvotes: 4

Views: 3560

Answers (4)

00prometheus
00prometheus

Reputation: 839

The function signature (the input and output types of your function) along with 2:nd order functions (functions that can be put in variables) take the role that an Interface has in object oriented languages. As long as the function signature matches the expected type, you can substitute one function for another.

For instance, assume a function f that takes two arguments: An integer a and a function g, where the function argument g should in turn be a function that takes an int and returns a str:

For example (in pseudocode for all that are curious about functional programming):

fun f(a: int, g:int->str) -> int

Just by declaring the parameter g, you have now created an interface: You can only pass a function for the parameter g that matches the signature of g, but as long as you match that signature, you can pass any function.

Upvotes: 2

amalloy
amalloy

Reputation: 92117

There are things like typeclasses, as the other answers say, but even more than that, there's one pervasive interface: a function. Many, many places where an object-oriented program would need some custom interface, a similar functional program can just use a function. eg, map f xs in haskell uses f, where an object-oriented program might use a Strategy or whatever to accomplish the same task.

Upvotes: 13

Incerteza
Incerteza

Reputation: 34934

data and newtype in Haskell are approximately equal to class in Java.

class in Haskell is approximately equal to interface in Java.

Upvotes: -2

Chad Gilbert
Chad Gilbert

Reputation: 36385

Haskell typeclasses fulfill some of the same roles as interfaces in object oriented languages.

Upvotes: 7

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