Reference

This page maps Yulang's top-level syntax, visibility, comments, and detailed reference topics. Use it to find a language construct; the guide presents the language in learning order.

Program structure

A Yulang program is a sequence of top-level statements. Statements are declarations (my, our, pub, struct, enum, act, role, impl, error, cast, type, use, mod) and bare expressions. The Playground evaluates bare expressions and shows the last root value; the CLI command yulang run --print-roots prints root expression values.

Visibility

Keyword	Meaning
my	Private binding, local or top-level
our	Exports a binding into the enclosing companion module
pub	Exports a binding from the module; also shows it in the Playground's Types pane

Comments

// Line comment.

/* Block comment. */

-- Single-line doc comment (not a line comment).

---
Multi-line doc block.
May contain markdown and ```yulang fences.
---

// and /* ... */ are ordinary comments. -- and --- blocks are documentation comments — they appear in syntax trees and tooling, so they are not interchangeable with //.

By topic

Surface syntax

• Syntax Style — when and how to drop parentheses
• Application & Operators — how f x, f(x), f: x, and f.method differ
• Operator Declarations — infix, prefix, suffix, precedence

Values and types

• Values & Types — the type universe
• Strings — string layout, escapes, interpolation
• Patterns — every pattern form
• Structs & Roles — struct, with:, role, impl
• Casts — cast(x: A): B, where the compiler inserts them

Computation

• Functions — declarations, currying, named arguments
• Control Flow — for, sub:, case, references
• Effects — act, catch, handler shapes
• Errors — error, fail, from, up, wrap

Style

• Idioms — what idiomatic Yulang looks like

Theory

• Type Inference Theory — what the inferer is doing under the hood

Standard library

• Core, list, str
• opt, result
• io::file, control::nondet