The MPL Reference
This reference describes the Meta Programming Language (MPL) and its Standard Library.
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| Question | Reference page | Scope |
|---|---|---|
| What do object, schema, view, known and stable mean? | Concepts | Definitions of the terms the rest of the Reference builds on, with the non-obvious rules behind them. |
| What syntax form is this? | Nodes | Node syntax, scope behavior, stack effects, and node-specific semantics. |
| What schema or schema group is this object? | Schemas | Schema kinds, schema groups, and shared schema-level vocabulary. |
| What builtin performs this operation? | Builtins | Language builtins, stack effects, constraints, and examples. |
| What Standard Library module provides this helper? | Standard Library | Standard modules, exported helpers, and module-specific examples. |
| How should MPL source be formatted? | Formatting | Source-code formatting conventions and idiomatic expression choices. |
| What exact grammar production accepts this text? | Grammar | The current compiler grammar in W3C EBNF. |
| How do I invoke the compiler? | Compiler | mplc invocation, options, module search paths, diagnostics, and LLVM IR output. |
| What does this compiler message mean? | Diagnostics | Every compile-time message: the condition that raises it, the fix, and the rule behind it. |
| What changed in the language and the library? | Changes | Behavior changes since April 2026, newest first, with the pages that state the current behavior. |