std:core

Core types and utilities available in every Pleno program.

Import

These types are available globally without explicit import.

Result Type

The Result<T, E> type represents either success (Ok) or failure (Err).

Ok<T>(value: T): Result<T, E>

Creates a successful result containing value.

fn divide(a: Float, b: Float): Result<Float, String> {
    if (b == 0.0) {
        return Err("Division by zero");
    }
    return Ok(a / b);
}

print(divide(10.0, 4.0).unwrap());  // 2.5

Run

Err<E>(error: E): Result<T, E>

Creates a failure result containing error.

let result = Err("File not found");
print(result.isErr());  // true

Run

Result Methods

• isOk() returns true for Ok.
• isErr() returns true for Err.
• unwrap() returns the value, or throws called unwrap on Err.
• unwrapOr(default) returns the value, or default for Err.
• expect(message) returns the value, or throws message.

let good = Ok(42);
let bad = Err("timeout");

print(good.isOk());        // true
print(bad.isErr());        // true
print(good.unwrap());      // 42
print(bad.unwrapOr(0));    // 0
print(good.expect("no value"));  // 42

Run

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Option Type

The Option<T> type represents an optional value.

Some<T>(value: T): Option<T>

Creates an option containing a value.

let users = ["Ada", "Grace"];

fn findUser(id: Int): Option<String> {
    if (id >= 0 && id < users.length) {
        return Some(users[id]);
    }
    return None;
}

print(findUser(0).unwrapOr("nobody"));  // Ada
print(findUser(9).unwrapOr("nobody"));  // nobody

Run

None: Option<T>

Represents the absence of a value.

let empty: Option<String> = None;
print(empty.isNone());  // true

Run

Option Methods

• isSome() returns true if there is a value.
• isNone() returns true if there is no value.
• unwrap() returns the value, or throws called unwrap on None.
• unwrapOr(default) returns the value, or default for None.
• expect(message) returns the value, or throws message.

let name = Some("Ada");
let missing: Option<String> = None;

print(name.isSome());               // true
print(missing.isNone());            // true
print(name.unwrap());               // Ada
print(missing.unwrapOr("unknown")); // unknown
print(name.expect("no name"));      // Ada

Run

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