Print Functions (`std:print`, `std:println`)

Write text to standard output or to any stream.

Overview

Printing is not built into the language — there is no prelude, so every program that prints must import the function it uses:

println(text = "", out = nil) → Number (bytes written)
print(text, out = nil) → Number (bytes written, no trailing newline)

Both live directly under std, not inside a submodule:

import std:println
import std:print

print("Hello, ")
println("world!")

Quick Start

import std:println

println("Hello, world!")
println(42)
println([1, 2, 3])
println()          # writes just a newline

`println(text = "", out = nil)`

Writes text followed by a newline and returns the number of bytes written.

text — any value. Non-string values are converted the same way value::to_string() converts them. Defaults to "", so println() prints an empty line.
out — a stream to write to. nil (the default) means standard output.

import std:println

n = println("hi")
println(n)  # 3

Values are rendered without quotes, and maps and tuples use Suji’s own display form rather than JSON:

import std:println

println("text")            # text
println(true)              # true
println(nil)               # nil
println([1, 2, 3])         # [1, 2, 3]
println({"a": 1, "b": 2})  # {a: 1, b: 2}
println((1, 2))            # (1, 2)

For JSON output use std:json instead:

import std:json
import std:println

println(json:generate({"a": 1, "b": 2}))  # {"a":1,"b":2}

`print(text, out = nil)`

Writes text with no trailing newline and returns the number of bytes written. Unlike println, text is required.

import std:print
import std:println

print("Loading")
print("...")
println(" done")  # Loading... done

Writing to a Stream

Pass a stream as the second argument. std:io exposes the standard streams, and io:open returns a writable stream for a file.

import std:io
import std:println

println("this goes to stderr", io:stderr)
println("this goes to stdout", io:stdout)

import std:io
import std:println

p = `mktemp`
f = io:open(p, true, true)
println("first line", f)
println("second line", f)
f::close()

r = io:open(p)
println(r::read_lines()::length())  # 2
r::close()

Because stderr is a separate stream, diagnostics can be kept out of a pipeline’s stdout:

import std:io
import std:println

report = |label, value| {
    println("processing ${label}", io:stderr)
    println(value)
}

report("row-1", 42)

Interpolation Instead of Concatenation

+ never mixes types, so build messages with ${...} interpolation rather than concatenating a string with a number:

import std:println

count = 3
println("found ${count} items")  # found 3 items

Gotchas

Nothing is imported implicitly. A snippet that calls println without import std:println fails with Undefined variable: println.
println returns a number, so calling it as the last expression of a function makes that function return the byte count rather than nil.
print has no default text: print() raises an arity mismatch.
Output is not buffered per line by the language; interleaving print to stdout and stderr may not appear in source order when both are redirected to the same file.

The Suji Programming Language