if expressions

Darts
Darts in F# 
module Darts

open System

let score (x: double) (y: double): int =
    let distance = Math.Sqrt(x * x + y * y)

    if   distance <=  1.0 then 10
    elif distance <=  5.0 then  5
    elif distance <= 10.0 then  1
    else 0

The first step is to calculate the distance from the center of the board, which we can with the cartesian coordinates distance formula

let distance = Math.Sqrt(x * x + y * y)

Before we'll look at the score calculation, let's re-iterate the games rules:

Lands Distance Points
Outside > 10 units 0
Outer circle > 5 units and <= 10 units 1
Middle circle > 1 unit and <= 5 units 5
Inner circle <= 1 unit 10

Directly translating this to code gives us:

if   distance <= 1.0 then 10
elif distance > 1.0 && distance <=  5.0 then 5
elif distance > 5.0 && distance <= 10.0 then 1
else 0

However, due to the order of evaluation, we know in our second condition, distance > 1.0 must always true as otherwise distance <= 1.0 would have been true. The same reasoning applies to the distandistance > 5.0 condition. We can thus shorten our code to:

if   distance <=  1.0 then 10
elif distance <=  5.0 then  5
elif distance <= 10.0 then  1
else 0
28th Aug 2024 · Found it useful?

Other Approaches to Darts in F#

Other ways our community solved this exercise
let score (x: double) (y: double): int =
    match Math.Sqrt(x * x + y * y) with
    | distance when distance <=  1.0 -> 10
    | distance when distance <=  5.0 ->  5
    | distance when distance <= 10.0 ->  1
    | _ -> 0
Pattern matching

Use pattern matching.