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#HASKELL FUNCTIONAL PROGRAMMING TUTORIAL SOFTWARE#
Web development, programming languages, Software testing & othersĪs we have discussed that to define a function in Haskell we have to follow some stander given by the Haskell official documentation which helps us to get the desired result as well, let’s take a closer look at the function declaration in Haskell for functions see below Īs you can see in the above line of syntax for function in Haskell, we first give the name followed by the list of arguments it takes and produces the output for us.
#HASKELL FUNCTIONAL PROGRAMMING TUTORIAL FREE#
class Eq a where ( = ) :: a -> a -> Bool ( /= ) :: a -> a -> Bool x = y = not ( x /= y ) x /= y = not ( x = y ) - This defines a typeclass that requires two functions, (=) and (/=) - It also declares that one function can be declared in terms of another - So it is enough that *either* the (=) function or the (/=) is defined - And the other will be 'filled in' based on the typeclass definition - To make a type a member of a type class, the instance keyword is used instance Eq TrafficLight where Red = Red = True Green = Green = True Yellow = Yellow = True _ = _ = False - Now we can use (=) and (/=) with TrafficLight objects canProceedThrough :: TrafficLight -> Bool canProceedThrough t = t /= Red - You can NOT create an instance definition for a type synonym - Functions can be written to take typeclasses with type parameters, - rather than types, assuming that the function only relies on - features of the typeclass isEqual ( Eq a ) => a -> a -> Bool isEqual x y = x = y - Note that x and y MUST be the same type, as they are both defined - as being of type parameter 'a'.Start Your Free Software Development Course The Eq typeclass is for types whose instances can - be tested for equality with one another. Typeclasses - Typeclasses are one way Haskell does polymorphism - They are similar to interfaces in other languages - A typeclass defines a set of functions that must - work on any type that is in that typeclass.
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Say we have the - following type synonyms and items with the following type signatures type Weight = Float type Height = Float type Point = ( Float, Float ) getMyHeightAndWeight :: Person -> ( Height, Weight ) findCenter :: Circle -> Point somePerson :: Person someCircle :: Circle distance :: Point -> Point -> Float - The following would compile and run without issue, - even though it does not make sense semantically, - because the type synonyms reduce to the same base types distance ( getMyHeightAndWeight somePerson ) ( findCenter someCircle ) - 8. This is fine: myPoint'2 = CartesianPoint2D 3.3 4.0 - It's also useful to pattern match data constructors in `case` expressions distanceFromOrigin x = case x of ( CartesianPoint2D x y ) -> sqrt $ x ** 2 + y ** 2 ( PolarPoint2D r _ ) -> r - Your data types can have type parameters too: data Maybe a = Nothing | Just a - These are all of type Maybe Just "hello" - of type `Maybe String` Just 1 - of type `Maybe Int` Nothing - of type `Maybe a` for any `a` - For convenience we can also create type synonyms with the 'type' keyword type String = - Unlike `data` types, type synonyms need no constructor, and can be used - anywhere a synonymous data type could be used.
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Even if a type is defined with record syntax, it can be declared like - a simple data constructor. Single line comments start with two dashes.