If you want to try F# but without the project setup it requires, then you might try one these which are easier:
Online dotnet compiler
Try F# using the online dotnet compiler. Don't forget to choose F# from the language dropdown on the left-hand side.
To follow the rest of this guide, you will need to install dotnet cli.
F# repl
You can write F# code interactively by using repl. The repl can be started by running dotnet fsi
in the command-line. Each statement you write should be terminated with double semicolons. To exit the repl, type Ctrl+D.
Use .fsx
extension
Typing directly into the repl can be hard, that is why F# lets you edit your code in a .fsx
file with your favorite editor and load it in the repl afterwards.
To do this, run dotnet fsi --use:<filename>
(Don't include < >).
Vscode with Ionide
Install Vscode and its Ionide extension. With this setup, you can highlight any code you want to test then hit alt-enter
to send it to the repl.
You could also use the arrow button in the top right-hand corner to send the whole file to the repl.
If you get fsi not found
error, you can fix it by enabling Fsharp: Use Sdk Scripts
in your Vscode settings.
Extra: Using multiple .fsx
files
To import some .fsx
file into your other .fsx
file, you can use #load
directive. For example, if you want to load B.fsx
in A.fsx
// B.fsx
let rec calculateFuel mass =
let fuel = (mass / 3) - 2
if fuel > 0 then fuel + calculateFuel fuel
else 0
// A.fsx
#load "B.fsx" // this loads B.fsx file
// Now you can either
B.calculateFuel 100
// or
open B
calculateFuel 100
Extra: Unit Testing .fsx
files
Simple testing can be done manually via the repl. In the event you need to do several tests after each change, you might write your tests in another .fsx
file. For Example, this is how I tested my code for day1 puzzle of advent of Code 2019
// Day01.fsx
let calculateFuel1 mass = (mass / 3) - 2
let rec calculateFuel2 mass =
let fuel = (mass / 3) - 2
if fuel > 0 then fuel + calculateFuel2 fuel
else 0
// Day01Test.fsx
#load "../Day01.fsx"
open Day01
let ``calculateFuel1: mass of 12`` = (calculateFuel1 12) = 2
let ``calculateFuel1: mass of 14`` = (calculateFuel1 14) = 2
let ``calculateFuel1: mass of 1969`` = (calculateFuel1 1969) = 654
let ``calculateFuel1: mass of 100756`` = (calculateFuel1 100756) = 33583
let ``calculateFuel2: mass of 14`` = (calculateFuel2 14) = 2
let ``calculateFuel2: mass of 1969`` = (calculateFuel2 1969) = 966
let ``calculateFuel2: mass of 100756`` = (calculateFuel2 100756) = 50346
Next, we load our test file in the repl. Our tests pass when all bindings in our test file evaluate to true. Notice how F# let us write descriptive names using double backticks.
Extra: Some Useful F# resources
F# for fun and profit is a comprehensive site for everything F# related. It also hosts many F# talks. Two videos which I recommend are Functional programming design patterns and Domain Modeling Made Functional.
F# collections docs I use this whenever I need to find a function such as map, scan, fold, pairwise, etc for operating on collections (List, Map, Seq, Set, etc).
Coursera's Programming Languages, Part A. This course teaches functional programming using standard ML, a language that shares many similarities with F#.
Top comments (1)
Another way to test out F# is to use dotNetCore.
This lets you develop full compilable (console) F# apps.