io

Standard input and standard output.

print writes to the same standard output as write and write_line, so all three interleave in the order they ran. Every read first writes out whatever has been written so far, so a prompt is on screen before the program waits for an answer.

import io

is_eof

def is_eof() -> Bool

Tells whether standard input has been read to the end. read_line answers "" both for an empty line and at the end of the input, and this is how a program tells the two apart.

Returns

true when nothing is left to read, false otherwise.

Example

read

def read() -> String

Reads everything left on standard input, from where the last read stopped to the end, line endings included.

Returns

The rest of the input, or "" when nothing is left.

Example

read_line

def read_line(prompt: String = "") -> String

Writes prompt, with no newline, then reads one line of standard input. The line ending is not part of the answer.

Parameters

• prompt: what to show before waiting for the line; nothing by default.

Returns

The line, or "" at the end of the input. Use is_eof to tell an empty line from the end.

Example

write

def write(text: String) -> ()

Writes text to standard output exactly as it is, with no newline after it. Use it to build a line from several pieces, and write_line or print to end it.

Parameters

• text: the characters to write.

Example

write_line

def write_line(text: String) -> ()

Writes text to standard output, then a newline. Unlike print, it takes exactly one string and writes it as it is.

Parameters

• text: the line to write, without its newline.

Example