Currying Functions in Scala



Currying is named after Haskell Curry, an American mathematician. He is known for his work in combinatory logic.

Currying is a means of transforming a function that takes more than one argument into a chain of calls to functions, each of which takes a single argument.

Let us consider the function below to calculate the final price of the product. The function takes in 3 parameters:

VAT (vat) for the region


Service charge (serviceCharge) of the shop


Product price (productPrice)


def finalPrice(vat: Double,

serviceCharge: Double,

productPrice: Double): Double =

productPrice + productPrice*serviceCharge/100 + productPrice*vat/100

But if you think about the function finalPrice again, a shopkeeper has to provide all the above values time and again whenever he wants to calculate the final price. Of course, that ignores the fact that the values of:

VAT is already defined for a country


Service charge for a shop is constant


So we will try to make life of our client a little bit easier. Let us define curried finalPrice:

def finalPriceCurried(vat: Double)

(serviceCharge: Double)

(productPrice: Double): Double =

productPrice + productPrice*serviceCharge/100 + productPrice*vat/100

We are taking this approach because our vat and serviceCharge will not change very often. So, let's use currying to split our method. We will declare a new val: vatApplied. I will provide the value of vat to the finalPriceCurried method and assign it to vatApplied.

val vatApplied = finalPriceCurried(20) _

Next, we will provide a service charge to my vatApplied val, and we will leave the price to be provided by the shopkeeper whenever they need it.

val serviceChargeApplied = vatApplied(12.5)

Let us test our serviceChargeApplied function to calculate the final price of the product.

val finalProductPrice = serviceChargeApplied(120)

finalProductPrice: Double = 159.0

We have reduced our method from accepting 3 parameters to accept one parameter. So, we have split our method in such a way that we don't have to provide all the arguments at the same time. I can provide these arguments whenever they are available. This transformation is called currying.

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