sys (System)

The sys module reaches outside the program: to the operating system’s random source, its environment, the command line, and the clock. These are the functions whose results the compiler cannot predict, which is why they live together in one module.

Import

import { random, randomInt, env, args, sleep } from sys;

double random()

Returns a pseudo-random double in [0.0, 1.0). Zero is possible, 1.0 is not. Takes no parameters.

import { random } from sys;

int main() {
    double r = random();
    print(r);     // e.g. 0.8846772796
    return 0;
}

The bytes come from the operating system’s CSPRNG, not from C’s rand(). That makes the sequence unpredictable, and it also means two runs of the same program produce different values. Where you need a repeatable run, do not call random().

int randomInt(int lo, int hi)

A random int in the half-open interval [lo, hi): lo can come back, hi cannot.

import { randomInt } from sys;

int main() {
    int dice = randomInt(1, 7);   // 1 through 6
    print(dice);
    return 0;
}

The upper bound being excluded is what makes randomInt(0, array.length()) always a valid index.

string? env(string name)

The value of an environment variable, or null when it is not set. The return type is string?, so the null case has to be handled before use.

import { env } from sys;

int main() {
    string? home = env("HOME");
    if (home != null) {
        print(home);
    } else {
        print("HOME is not set");
    }
    return 0;
}

string[] args()

The arguments passed to the program, in order.

import { args } from sys;

int main() {
    string[] a = args();
    int i = 0;
    while (i < a.length()) {
        print(a[i]);
        print("\n");
        i = i + 1;
    }
    return 0;
}

Arguments intended for the program go after --, which separates them from the compiler’s own flags:

saqut run prog.sqt -- hello world

a[0] = "hello"
a[1] = "world"

a[0] is the first argument, not the program name. The array holds only what follows --, so a program run with no arguments gets an empty array and a.length() is 0.

void sleep(int millis)

Pauses the program for the given number of milliseconds. The parameter is an int: sleep(1500) waits a second and a half, while sleep(1.5) is a compile error, because a float literal cannot be used where an int is expected.

import { sleep } from sys;

int main() {
    print("waiting...\n");
    sleep(1500);
    print("done\n");
    return 0;
}

Determinism

random(), randomInt(), and env() read state from outside the program, so the same source can produce different output on two runs. Everything else in saQut’s standard library is a pure calculation on the values you pass in. When a program has to be reproducible, this module is where to look first.