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About IO

Like most programming language Gleam has "side effects", so functions can read and change the state of the world, as well as returning a value.

The gleam/io module in the Gleam standard library provides functions for printing strings to the console.

io.println("Hello, Joe!")
// Hello, Joe!
// -> Nil

Other packages may provide other IO functions, such as simplifile, a package which provides functions for reading and writing files.

simplifile.read("favourite-colour.txt")
// -> Ok("Pink\n")