From Scala to Haskell

Defining case classes (product types)

Scala

case class Point(x: Int, y: Int)

Haskell

data Point = Point { x :: Int
                   , y :: Int
                   }

If you need your datatype to be visible outside of the file, in which it's defined, then remember to export it:

module YourModule ( Point(Point) )

Defining product types with some typeclasses derived

Scala

case class Point(x: Int, y: Int)

Haskell

 -- this needs to be at the top of a file
{-# LANGUAGE DeriveGeneric #-}

data Point = Point { x :: Int
                   , y :: Int
                   } deriving (Eq, Generic Show)

Eq - with instance of that typeclass (Point 1 1) == (Point 123 321) will compile.
Generic - you can think of it as kind of shapeless.LabelledGeneric - something that is a base for other typeclass derivation mechanisms. For example aeson (JSON library) can generate codecs for your data type providing it has an instance of Generic. I know it sounds vague but my current understanding is vague too.
Show - with instance of that typeclass you can show (Point 1 1) which returns a string. We can compare it to toString mechanism known from JVM world.

You don't need {-# LANGUAGE DeriveGeneric #-} if you don't want to derive Generic - you would still be able to derive e.g. Show.

Instantiating case classes

Scala

Point(3, 15)

Haskell

Point 3 15

Accessing fields

Scala

Point(3, 15).x

Haskell

x (Point 3 5)

It will work only if you exported `x` and imported it to scope where you use it. You can export field accessors with:

module YourModule ( Point(Point, x, y) ) where ...

.copy on case classes

Scala

Point(3, 15).copy(y = 100)

Haskell

(Point 3 15) { y = 100 }

Defining sealed trais hierarchy (sum types)

Scala

sealed trait Colour

case object Black extends Colour
case object Grey  extends Colour
case object Grey  extends Colour

Haskell

data Colour = Black
            | Grey
            | White

In order to be able to use data constructors you need to export them with:

module YourModule ( Colour(Black, Grey, White) ) where ...

ADTs (product types and sum types)

Scala

sealed trait ClientError

case class ParsingError(input: String, msg: String)
case class HostUnavailable(host: String)
case object OtherError

Haskell

data ClientError = ParsingError { input :: String, msg :: String }
                 | HostUnavailable { host :: String }
                 | OtherError