The Mog Language Guide

Mog is a new statically typed, compiled, embedded programming language designed to be written by LLMs and AI agents. It fits its full spec in 3200 tokens, compiles to native code via a safe Rust toolchain using the QBE backend, and uses a capability-based permission system so host applications control exactly what a Mog program can do. Key features include async/await, tensor support, no operator precedence, no implicit type coercion, and no uninitialized variables. It targets three agent use cases: one-off scripts, recurring hooks in the agent loop, and extending the agent itself. The compiler was built using the Volt coding agent over a three-week session. The language guide covers syntax basics including variables, types, operators, and control flow across multiple chapters.

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Mar 09•3h 24m read time•From moglang.org

Table of contents

Overview Examples Why Mog?Alternatives The Language The Capability System The Compiler Current Status Hello, World How Mog Programs Are Compiled and Run Program Structure Comments Print Functions A More Complete Example What Mog Is Not What’s Next Creating Bindings with :=Reassignment with =Type Annotations Shadowing Practical Examples Summary Scalar Types Type Conversions Operators Flat Operators (No Precedence)Common Patterns Summary If/Else While Loops For Loops Break and Continue Match Practical Examples Summary Basic Function Declarations Void Functions Parameters and Return Types Named Arguments and Default Values Calling Conventions Recursion Math Builtins Other Builtins Summary Closure Syntax Capturing Variables Type Aliases for Function Types Passing Closures to Functions Returning Closures from Functions Closures with Array Methods Summary String Basics String Interpolation String Concatenation String Methods String Slicing String Comparison Conversions Print Functions Building Strings Summary Declaring Structs Constructing Instances Field Access Field Mutation Passing Structs to Functions No Methods — Use Standalone Functions Constructor Functions Nested Structs Structs with Arrays and Maps Practical Examples Summary Arrays Maps SoA (Struct of Arrays)Putting It All Together Summary Result<T>Optional ?T The ? Propagation Operator try-catch Blocks Match Patterns for Result and Optional Practical Patterns Summary Async Functions Await Spawn all() — Wait for All race() — Wait for First Error Handling with Async Summary Package Declaration Public vs Private — The pub Keyword Importing Packages Multi-Import Syntax Qualified Access The Module File Circular Import Detection Practical Example: Splitting a Program into Packages Summary The Capability Model Declaring Capabilities: requires and optional Built-in Capabilities Practical Examples Conventional Capabilities Custom Host Capabilities Summary The Embedding Lifecycle The Embedding API Implementing a Custom Capability MogValue: Data Exchange Between Host and Script Resource Limits and Timeouts Safety Guarantees Practical Example: Embedding in a Game Server Summary Plugins — Dynamic Loading of Mog Code How Mog Compares to Other Embeddable Languages What Are Tensors?Creating Tensors Tensor Properties Element Access Shape Operations Tensors and Host Capabilities Practical Examples Summary Type Aliases With Blocks Struct-of-Arrays (SoA) Performance Compilation Backend: rqbe The Interrupt System Memory Management What Mog Does NOT Have 1. FizzBuzz 2. Fibonacci Sequence 3. Word Frequency Counter 4. Simple Calculator with Error Handling 5. Data Validation Chain 6. Sorting and Filtering Pipeline 7. Matrix Operations 8. Agent Tool-Use Script 9. Recursive Tree Traversal 10. Async Pipeline Summary

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