Mochi Enhancement Proposals

A MEP is a design document for the Mochi language, type system, and toolchain. The full process is described in MEP 0. The list below is generated from the frontmatter of every mep-NNNN.md file in the docs tree, so new proposals appear here automatically once npm run gen:meps (or any npm start / npm run build) regenerates the manifest.

All MEPs

MEP	Title	Status
`0000`	Index of Mochi Enhancement Proposals Index of Mochi Enhancement Proposals.	Active
`0001`	Lexer Mochi's token classes, reserved words, lexical errors, and conformance corpus, specified end-to-end with no corner cases.	Informational
`0002`	Grammar Mochi's PEG grammar in full, with the design principles and conformance obligations that fix the language.	Informational
`0003`	Abstract Syntax Tree Mochi's AST as a closed family of tagged unions, the encoding that makes parse output unambiguous, and the soundness invariants every consumer can rely on.	Informational
`0004`	Type System The kinds, the comparisons, the numeric tower, and the places where Mochi's type system does not yet do what it claims.	Informational
`0005`	Type Inference Strict static algebraic type inference. Principal types, no implicit any, no null.	Standards Track
`0006`	Type Checker Entry point, builtin environment, statement walk, and the diagnostic catalogue.	Informational
`0007`	Soundness Progress, preservation, and the test obligations that prove them.	Active
`0008`	Test Strategy The five test layers, the golden harness, and the TAPL chapter mapping.	Active
`0009`	Fixture Catalogue Inventory of parser and type fixtures with a property coverage matrix.	Informational
`0010`	Known Gaps and Weakness Review Catalogue of soundness gaps, surprising behavior, and tracked follow-ups.	Informational
`0011`	Subtyping and Variance A separate subtype predicate, the variance lattice, and the closure of any.	Active
`0012`	Parametric Polymorphism System-F-lite call-site inference, fresh type variables, and the end of any-builtins.	Active
`0013`	Algebraic Data Types and Match Struct and union typing rules, match exhaustiveness, irredundancy, and recursive types.	Draft
`0014`	Query Algebra LINQ-shaped query expressions, clause-by-clause type rules, and aggregate semantics.	Informational
`0015`	Effects A labeled effect system over function types. Pure by default, inferred from the body, annotatable at module boundaries, enforced where purity matters.	Draft
`0016`	Null Safety Total option discipline with no force unwrap, flow narrowing, safe-call and coalesce operators, and a no-panic guarantee.	Draft

Process

MEP	Title	Status
`0000`	Index of Mochi Enhancement Proposals Index of Mochi Enhancement Proposals.	Active
`0007`	Soundness Progress, preservation, and the test obligations that prove them.	Active
`0008`	Test Strategy The five test layers, the golden harness, and the TAPL chapter mapping.	Active

Informational

MEP	Title	Status
`0001`	Lexer Mochi's token classes, reserved words, lexical errors, and conformance corpus, specified end-to-end with no corner cases.	Informational
`0002`	Grammar Mochi's PEG grammar in full, with the design principles and conformance obligations that fix the language.	Informational
`0003`	Abstract Syntax Tree Mochi's AST as a closed family of tagged unions, the encoding that makes parse output unambiguous, and the soundness invariants every consumer can rely on.	Informational
`0004`	Type System The kinds, the comparisons, the numeric tower, and the places where Mochi's type system does not yet do what it claims.	Informational
`0006`	Type Checker Entry point, builtin environment, statement walk, and the diagnostic catalogue.	Informational
`0009`	Fixture Catalogue Inventory of parser and type fixtures with a property coverage matrix.	Informational
`0010`	Known Gaps and Weakness Review Catalogue of soundness gaps, surprising behavior, and tracked follow-ups.	Informational
`0014`	Query Algebra LINQ-shaped query expressions, clause-by-clause type rules, and aggregate semantics.	Informational

Standards Track

MEP	Title	Status
`0005`	Type Inference Strict static algebraic type inference. Principal types, no implicit any, no null.	Standards Track
`0011`	Subtyping and Variance A separate subtype predicate, the variance lattice, and the closure of any.	Active
`0012`	Parametric Polymorphism System-F-lite call-site inference, fresh type variables, and the end of any-builtins.	Active
`0013`	Algebraic Data Types and Match Struct and union typing rules, match exhaustiveness, irredundancy, and recursive types.	Draft
`0015`	Effects A labeled effect system over function types. Pure by default, inferred from the body, annotatable at module boundaries, enforced where purity matters.	Draft
`0016`	Null Safety Total option discipline with no force unwrap, flow narrowing, safe-call and coalesce operators, and a no-panic guarantee.	Draft