Press ‘F5’

The F5 button is the magic button to start debugging. However, if you start debugging the first time, you need to set up VisualStudio Code first. You need to setup a launch.json file to start debugging and a tasks.json file to first run the process.

Setup

• Press F5
• Select .NET Core

• VS Code generates the launch.json file in the .vscode folder and opens it.

• Edit the launch.json file
• Insert the configuration entry within the selected square brackets of the ‘configuration’ section
  • Press Ctrl + Space Bar
  • Select .NET: Launch .NET Core Console App
  • Enter the path to the application .dll file in the program attribute:
    "${workspaceFolder}/src/MailBoxTransformer/bin/Debug/netcoreapp3.1/MailBoxTransformer.dll"
  • The path differs from the original template because the project is within the src sub-folder.

• Press F5 again
• VS Code now complains that it does not find the build task defined in the preLaunchTask attribute of the launch.json file
• Select Configure Task

• Select Create tasks.json file from template

• Choose the .NET Core Executes .NET core build command template

• VS Code generates the tasks.json file in the .vscode folder and opens it.

• Edit the tasks.json file
• If the .fsproj file is not in the main folder
• Insert the path of the directory containing the .fsproj file as an additional argument for dotnet build.
  • "${workspaceFolder}/src/MailBoxTransformer",
• To see the logs of the build task in the console (optional):
  • Change the presentation attribute in the tasks.json file
    from "silent" to "always"

• Press F5 again
• VS Code runs
  • The dotnet build process
  • The app
• Add the launch.json and the tasks.json files located in the .vscode folder to your source control system (e.g. git).

You are now able to start the build process and the app itself from within VS Code. Now you can set break points and debug your app. I have included the complete launch.json and the tasks.json files below. Have fun!

launch.json

• Located in the .vscode folder

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": ".NET Core Launch (console)",
            "type": "coreclr",
            "request": "launch",
            "preLaunchTask": "build",
            "program": "${workspaceFolder}/src/MailBoxTransformer/bin/Debug/netcoreapp3.1/MailBoxTransformer.dll",
            "args": [],
            "cwd": "${workspaceFolder}",
            "stopAtEntry": false,
            "console": "internalConsole"
        }
    ]
}

tasks.json

• Located in the .vscode folder

{
    // See https://go.microsoft.com/fwlink/?LinkId=733558
    // for the documentation about the tasks.json format
    "version": "2.0.0",
    "tasks": [
        {
            "label": "build",
            "command": "dotnet",
            "type": "shell",
            "args": [
                "build",
                "${workspaceFolder}/src/MailBoxTransformer",
                // Ask dotnet build to generate full paths for file names.
                "/property:GenerateFullPaths=true",
                // Do not generate summary otherwise it leads to duplicate errors in Problems panel
                "/consoleloggerparameters:NoSummary"
            ],
            "group": "build",
            "presentation": {
                "reveal": "always"
            },
            "problemMatcher": "$msCompile"
        }
    ]
}

References

• Video: F# Basics 003 – Debugging F# Applications in VS Code
• Video: F# on .NET Core – Debugging in Code

Create a console app with the CLI

dotnet new console -lang "F#" -o src/MyConsoleApp

Run the app in the terminal

The easy way: Move first to the folder with the .fsproj file and then use dotnet run without any arguments:

cd src/MyConsoleApp
dotnet run

If you want to start the app from a location different than the one containing the .fsproj file, you need to enter the argument --project with the path to the .fsproj file.

dotnet run --project src/MyConsoleApp/MyConsoleApp.fsproj 

References

• https://docs.microsoft.com/en-us/dotnet/fsharp/get-started/get-started-vscode
• https://docs.microsoft.com/en-us/dotnet/fsharp/get-started/get-started-command-line
• https://atlemann.github.io/fsharp/2018/02/28/fsharp-solutions-from-scratch.html
• http://ionide.io/

Lately, I wanted to code some F# scripts. I started up Visual Studio Code on my MacBook and created an fsx file. Then I noticed that intellisense was not working anymore despite active code highlighting. That was the start for a long journey. I ended up on installing (again):

• .NET Core 3.1 SDK
• Mono 6.6.0 (Visual Studio channel) (I am not shure anymore if I still need mono)
• Visual Studio Code (Here I only checked if there are updates available)
• Ionide-fsharp 4.6.3 extension for Visual Studio Code

Intellisense was now working in F# projects and somehow/sometimes in fsx files within the context of an F# project. Then I tried it out in a stand-alone fsx file. Intellisense was not working again… Then I found some notes about the ‘FSharp.useSdkScripts’ option of the ionide-fsharp extension of Visual Studio Code. I activated the setting:

What a wonder, intellisense is working for F# fsx script files! With this setting enabled, I am no longer working with mono but with the .NET Core version of fsi (FSharp Interactive). With that, I think I don’t actually need mono.

References

• https://github.com/ionide/ionide-vscode-fsharp/issues/1275