std/io¶

Console input and output: write lines to standard output and read lines from standard input. The functions here are free functions, so you import the ones you need by name.

import std/io { println, input }

fun main() {
    let name = input("Your name: ")
    println("Hello, ${name}")
}

Importing¶

import std/io { print, println, input, read_line }

std/io is a set of free functions, so use a selective import and list the names you want. A bare import std/io does not bring the functions into scope.

The global `print` builtin¶

You do not need std/io to print. The print builtin is always in scope and accepts any value whose type implements ToString, so it works on numbers, booleans, and your own types without conversion:

fun main() {
    print(42)               // 42
    print(true)             // true
    print(3.14)             // 3.14
}

The print function from std/io is the String-only form below. The always-available builtin is the more convenient choice for most output; reach for std/io when you want println, input, or read_line.

Output¶

`print(s: String)`¶

Write s to standard output with no trailing newline. The argument must be a String; build one with interpolation or std/string methods if you have other values to include.

import std/io { print }

fun main() {
    print("no newline here")
    print(" and more on the same line")
}

`println(s: String)`¶

Write s to standard output followed by a newline.

import std/io { println }

fun main() {
    println("first line")
    println("second line")
}

Input¶

`input(prompt: String) -> String`¶

Write prompt to standard output with no trailing newline, then read one line from standard input and return it without its trailing newline. At end of input the returned string is empty.

import std/io { input }

fun main() {
    let answer = input("Continue? (y/n) ")
    if answer == "y" {
        print("ok")
    }
}

`read_line() -> String`¶

Read one line from standard input and return it without its trailing newline, printing no prompt. At end of input the returned string is empty, which is how you detect that the stream is exhausted.

import std/io { read_line }
import std/string

fun main() {
    let line = read_line()
    print(line.trim().to_upper())
}

Worked example: echo non-empty lines¶

Read lines until the input ends, skipping blank ones. The empty string from read_line at end of input ends the loop.

import std/io { read_line, println }
import std/string

fun main() {
    let line = read_line()
    while !line.is_blank() {
        println(line.trim())
        line = read_line()
    }
}

std/io¶

Importing¶

The global print builtin¶

Output¶

print(s: String)¶

println(s: String)¶