# Mps Language Inheritance

> Investigate inheritance between MPS languages and between concepts — extended languages, superconcepts, implemented interfaces, sub-/assignable concepts, and cross-language specialization. Use when tracing language hierarchies, finding extension points, or checking concept assignability.

- Skill: `jetbrains/mps-language-inheritance` (Agent Skill)
- Install (CLI): `npx skillmds@latest add jetbrains/mps-language-inheritance`
- Raw SKILL.md: https://api.skillmd.com/api/skills/jetbrains/mps-language-inheritance/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: jetbrains (https://skillmd.com/u/jetbrains)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/jetbrains/mps-language-inheritance

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# MPS Language and Concept Inheritance

Two layers of inheritance matter in MPS: module-level (one language `extends` another) and concept-level (concepts inherit superconcepts and implement interface concepts).

## Critical Directives

- **Concept-level inheritance is realized through module-level extension** — different `languageReference` on a concept and its `superConcept` indicates a cross-language specialization, which usually requires the consumer's language to extend the parent.
- **`GET_ALL_SUPERCONCEPTS`** gives the full transitive closure in a single call — prefer it over recursive walking of `superConcept` / `superInterfaces`.
- **`IS_SUBCONCEPT_OF`** is the fastest way to verify a single assignability question; do not enumerate `GET_SUB_CONCEPTS` and search by hand.

## Module-Level Inheritance (Language Extension)

One language can inherit the structure and functionality of another via an "extends" relationship.

1. **Tool**: `mps_mcp_get_project_structure` (with `includeDependencies: true`).
2. **Workflow**: check the `extendedLanguages` field in the response for the target language. This lists direct parent languages.
3. **Hierarchy tracing**: recursively call this tool for each parent to build the full inheritance tree.

## Concept-Level Inheritance

### Upward Hierarchy (Ancestors)

* **Direct ancestors**: use `mps_mcp_get_concept_details`. The response includes:
    * `superConcept`: immediate parent concept.
    * `superInterfaces`: immediate implemented interface concepts.
    * `superConceptContainingProject` and `superInterfaceDetails[*].containingProject` when an ancestor comes from another open MPS project and is read-only from the selected project.
* **Full closure**: use `mps_mcp_query_structure` with `GET_ALL_SUPERCONCEPTS` to get the complete chain of ancestors and interfaces in one call.

### Downward Hierarchy (Descendants)

* **Specializations**: use `mps_mcp_query_structure` with `GET_SUB_CONCEPTS` to find all concepts (direct and indirect) inheriting from a base.
* **Implementations**: use `GET_ASSIGNABLE_CONCEPTS` to retrieve only non-abstract subconcepts that can be instantiated.

## Strategic Analysis

* **Verification**: use `mps_mcp_query_structure` with `IS_SUBCONCEPT_OF` to check if concept A inherits from concept B.
* **Cross-language extension**: compare the `languageReference` of a concept with that of its `superConcept`. Different references indicate a language boundary specialization; foreign-project ancestors are marked explicitly with the containing-project fields.
* **Discovery**: use `mps_mcp_search_concepts` to find base concepts (e.g. "Statement") for extension.
* **Implicit dependencies**: if a model uses a language without an explicit import, check if its used languages extend the missing language via `mps_mcp_get_project_structure`.

## Best Practice

Identify extension points by first checking high-level `extendedLanguages` via `mps_mcp_get_project_structure`, then use `mps_mcp_get_concept_details` to pinpoint cross-language concept specializations.

## Related Skills

- **`mps-language-analysis`** — start here when you need general language inspection, not just inheritance.
- **`mps-aspect-structure-concepts`** — when you intend to define new concepts (with their own super/interface lists).
- **`mps-aspect-accessories`** — for `extendedLanguages` vs `usedLanguages` semantics at module level.