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Brian Berns
Brian Berns

Posted on

F# Tip 2: Use the pipe operator

F#'s pipe operator |> lets you chain function calls together easily:

let car =
    Car.create Red
        |> Car.drive 10000
        |> Car.paint White
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This creates a red car, drives it 10000 miles, and then paints it white. If you're familiar with "fluent" coding in C#, you'll see a strong similarity:

// C#
var car =
    new Car(Color.Red)
        .Drive(10000)
        .Paint(Color.White);
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Note that the pipe operator leverages partial function application. For example, the Car.drive function takes two arguments:

let drive miles car =
    { car with Mileage = car.Mileage + miles }
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When we call it using the pipe operator, we specify all the arguments except the last one, and then invoke the resulting "curried" function with the pipe operator:

car |> Car.drive 50
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When designing an F# API, it's important to put the "primary" argument last in the function signatures. For example, we collect all Car-oriented functions in a Car module, and list the car argument last in each one:

module Car =

    let create color =
        { Mileage = 0; Color = color }

    let drive miles car =
        { car with Mileage = car.Mileage + miles }

    let paint color car =
        { car with Color = color }
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Top comments (3)

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saint4eva profile image
saint4eva • Edited on

Nice tutorial. I have a question. Why not this:

var car = new Car(Color.Red)
.Drive(10000)
.Paint(Color.White);

Instead of this:

var car =
new Car(Color.Red)
.Drive(10000)
.Paint(Color.White);

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shimmer profile image
Brian Berns • Edited on

You’re right, that would probably be better for C#. I added a carriage return to emphasize the similarity with the F# syntax (which requires the carriage return).

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saint4eva profile image
saint4eva

okay.

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