moonbit-skills

Tracks deprecated MoonBit syntax to avoid generating invalid code. Reference this before writing MoonBit code. Auto-maintained when deprecated patterns are discovered.

Guide to solving the Expression Problem in MoonBit using Finally Tagless encoding, two-layer architecture (tagless + concrete AST), polymorphic trait methods, and related patterns. Use when designing extensible data types, adding new variants or operations to existing code, working with Finally Tagless, Object Algebras, open recursion, or discussing extensibility trade-offs in MoonBit.

Use BEFORE any performance optimization in MoonBit. Requires reproducing the claimed bottleneck in an isolated microbenchmark before designing a solution. Triggers on "optimize", "performance", "bottleneck", "slow", "speed up", or any TODO item citing millisecond costs. Do NOT skip this for "obvious" optimizations.

Execution discipline for boundary-crossing MoonBit refactors: splitting packages with language-enforced isolation via `internal/`, extracting modules behind a `pub using` facade, splitting files safely, and pinning invariants with property tests before structural change. Use when the task is "split this package", "extract these files into an internal package", "verify the public API didn't change", or "set up tests before refactoring". Pairs with `moonbit-refactoring`, which covers *what* to refactor toward.

Reference guide for effective trait usage in MoonBit's Self-based trait system (no trait type parameters, no associated types, but polymorphic trait methods are supported in v0.10+). Use when writing MoonBit traits, designing APIs with traits, or when the user asks about trait patterns like endomorphisms, capability traits, polymorphic methods, callback-based iteration, trait multiplication, newtypes, visitor pattern, or defunctionalized associated types in MoonBit.

Set up MoonBit project instructions and agent configuration for coding assistants. Use when bootstrapping agent guidance, validation commands, hooks, project conventions, or shared MoonBit context for Codex, Claude Code, or other agent environments.

Error handling conventions for MoonBit projects. Use when designing error types, choosing between abort/fail/raise, writing catch blocks, defining FFI boundaries, or reviewing error handling patterns. Triggers on: error handling, abort, fail, raise, catch, Result, error types, fallible functions, boundary safety, error recovery.

Repo maintenance for MoonBit projects. Five subcommands: default (full audit-and-fix pipeline), check (fast read-only health check), fix (full check + auto-fix only), triage (project direction + branch pruning), release (pre-release prep). Use at session start, before commits, weekly for direction, and before releases.

Implements opaque/newtype pattern in MoonBit for user-friendly public APIs. Use when designing type-safe wrappers, facade layers, or hiding implementation details in MoonBit libraries.

Quality checklist for MoonBit development. Use when implementing or modifying MoonBit code to catch dependency issues, syntax mistakes, test failures, CLI bugs, and interface changes before they become problems.