F# print functions

last modified May 1, 2025

In this article we cover the print functions in F# language.

In F#, we can use the built-in Console.WriteLine function to print to the terminal or the special F# helper printf and printfn functions.

Console.WriteLine

The Console.WriteLine is the core .NET function to print to the standard output.

main.fsx

open System

let name = “John Doe” let occupation = “gardener”

Console.WriteLine($"{name} is a {occupation}")

In the example, we print a message with Console.WriteLine. The function is available in the System namespace.

Console.WriteLine($"{name} is a {occupation}")

We use string interpolation to build the message.

$ dotnet fsi main.fsx John Doe is a gardener

The printf function

The printf function prints to standard output using the given format.

main.fsx

let name = “John Doe” let occupation = “gardener”

printf “%s is a %s\n” name occupation

The example prints a message to the console with printf.

printf “%s is a %s\n” name occupation

The function takes a format string as its first parameter. In the format string, we define placeholders that are replaced with values of the following parameters. The %s special placeholder is replaced with the string value.

The printfn function

The printfn function prints to standard output using the given format and adds a newline.

main.fsx

printfn “The bool is %b” (5 > 0) printfn “Binary is %B” 123 printfn “The char is %c” ‘F’ printfn “The string is %s” “falcon or "falcon" " printfn “The int is %i” -3 printfn “The int is %d” 42 printfn “The float is %f” 42.0 printfn “The HEX is %X” 42 printfn “The float is %e” 0.0000042

We print values to the terminal with printfn. We present various format specifiers.

$ dotnet fsi main.fsx The bool is true Binary is 1111011 The char is F The string is falcon or “falcon” The int is -3 The int is 42 The float is 42.000000 The HEX is 2A The float is 4.200000e-006

The sprintf function

The sprintf function does not print to the console. It builds a message (‘prints’ to a variable).

main.fsx

let name = “John Doe” let occupation = “gardener”

let msg = sprintf “%s is a %s” name occupation printfn “%s” msg

The example formats a message with sprintf and prints it to the console with printfn.

$ dotnet fsi main.fsx John Doe is a gardener

In this article we have worked with print functions in F#.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.