F# print functions
last modified July 18, 2023
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.
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.
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.
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).
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#.