Library

The standard library

The prelude that ships with the compiler, written in the language itself and in scope in every program.

since 0.1.0-alpha.1linuxwindowswasm

Description

The standard library is called the prelude. It is a set of ordinary source files written in Leviathan, on top of a small set of native operations, and it ships inside the compiler. You do not install it and you do not import it. Every program is compiled together with it, and every name it declares is in scope from the first line.

The prelude lives in the std namespace, and std is implicitly imported: it behaves as if every file began with uses std;. You can write Array, Map or sum(xs), and you can equally write the qualified form std::sum(xs). Some parts are placed in their own top-level namespaces with short names, notably math (math::pi), regex and env. Because the prelude is written in the language, you can read its sources as examples of ordinary Leviathan code.

One part of the prelude is only present for one target. The browser interface of the WebAssembly target is loaded when you build for a WebAssembly target and is invisible to native builds.

A little of everything, with no imports

Array<string> words = ["pear", "fig", "apple"];
Map<string, int> lengths = Map();
for (string w in words) { lengths = lengths.with(w, w.length()); }
console.writeln(lengths);
Set<int> sizes = Set(lengths.values());
console.writeln(sizes.length());
console.writeln(math::max(lengths.at("fig"), lengths.at("pear")));
Regex vowels = Regex("[aeiou]");
console.writeln(vowels.count("apple"));
StringBuilder sb = StringBuilder();
for (int i in 1..3) { sb.add(i.toString()); }
console.writeln(sb.toString());

Run it ▶

{pear: 4, fig: 3, apple: 5}
3
4
2
123

Where things are

This chapter's companion pages cover the core types.

Collections. Array<T>, Map<K, V> and Set<T> are pure values; see lang.collection-value-semantics for the shared rule. Range is the value of a..b. Pair and Triple are small value types, and OrderedArray is the result of a multi-key sort.
Iteration. The IIterable and IIterator interfaces and the for-in rules are in lang.iterator-protocol, and Seq is the lazy pipeline built on them.
Text tools. StringBuilder accumulates a long string, and Regex with the regex namespace does pattern matching in time linear in the input.
Numbers. The math namespace holds the constants and the transcendental functions.

The rest of the library has its own pages: the primitive types with their methods, Promise and tasks, streams and files, networking, Console, byte buffers (Block), processes and terminals. The generated library reference lists every type and method with its signature and examples.

Rules

No import is needed to use the prelude; std is implicitly in scope.
A prelude name can be written bare (sum) or qualified (std::sum).
math, regex and env are namespaces of their own and are written with their own prefix: math::pi, regex::isMatch(...).
Do not give your own classes the names of the built-in collections (Array, Map, Range) if you iterate over them with for-in: the loop recognises the built-in types by name.

Examples

Bare and qualified names

console.writeln(sum([1, 2, 3]));
console.writeln(std::sum([1, 2, 3]));
console.writeln(std::min([5, 3]));
Pair<int, int> p = Pair::Of(1, 2);
console.writeln(p.toString());
console.writeln(math::max(1, 2));