ENG Documentation

ENG (the executable is eng) is a small programming language whose syntax is written as structured English.

Programming in plain English — with a fixed grammar that the interpreter can parse deterministically.

This documentation describes the syntax implemented by the current Engling v0.1.0 interpreter.

Quick start

Run a source file:

cargo run -- run examples/01_hello.eng

Or, after building the binary:

eng run program.eng

Start the REPL by running eng without a subcommand:

eng

A minimal program:

Let greeting be "Hello, world.".
Print greeting.

Every statement ends with a period (.). Blocks such as If, Repeat, While, and function bodies end with End..

What ENG supports

• Variables and assignment
• Numbers, strings, booleans, lists, functions, and nothing
• Arithmetic and comparisons
• Boolean and / or
• If / Otherwise
• Repeat and While
• Functions with parameters and return expressions
• Lists with ordinal indexing
• Modules and selective imports
• An optional GUI feature using egui/eframe
• A bytecode compiler and stack-based virtual machine

Documentation map

• Getting Started
• CLI
• Syntax
• Variables
• Data Types
• Operators
• Conditions
• Loops
• Functions
• Lists
• Strings
• Modules and Imports
• REPL
• Errors and Debugging
• GUI
• Project Structure
• Architecture
• Grammar Reference
• Examples
• FAQ

Version note

The syntax documented here is based on the source tree supplied with this documentation. ENG is intentionally strict: it accepts known sentence templates rather than arbitrary English prose.