# Mps Model Manipulation > Use when writing or editing MPS BaseLanguage code that lives inside a model — behavior methods, typesystem rules, checking rules, generator queries, constraints, intentions, scope/canBe callbacks, dataflow builders — and combines the `smodel`, `collections`, and `closures` language extensions. Covers querying nodes (`.descendants`, `.ancestor`, `.children`, `.parent`, `containingRoot`), filtering sequences (`.where`, `.select`, `.translate`, `.ofConcept`), building closures (`{ it => ... }`, `yield`, recursion), creating and mutating nodes (`new node()`, `add new(C)`, `set new(C)`, `replace with new(C)`, `.detach`, `.copy`), property and link access (`SPropertyAccess`, `SLinkAccess`, `SLinkListAccess`), reference operations (`.reference/C : role/`, `.target`), null-safe node equality (`:eq:` / `:ne:`), smodel/Java type casts (`node:C`, `node as C`, `/`, `downcast`), foreach choice, the `command` / `read action` lock wrappers, and JSON blueprints for every shape the Java parser cannot produce. - Skill: `jetbrains/mps-model-manipulation` (Agent Skill, multi-file: 19 files) - Install (CLI): `npx skillmds@latest add jetbrains/mps-model-manipulation` - Raw SKILL.md: https://api.skillmd.com/api/skills/jetbrains/mps-model-manipulation/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: jetbrains (https://skillmd.com/u/jetbrains) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/jetbrains/mps-model-manipulation --- # Writing MPS BaseLanguage with smodel / collections / closures Use this skill when authoring code inside an MPS model where BaseLanguage is mixed with the `smodel`, `collections`, and `closures` extensions: behavior methods, checking/typesystem/dataflow rules, generator query functions, intentions, constraints, scope/canBe callbacks. The `mps_mcp_parse_java_and_insert` parser understands only plain Java, so most non-trivial code requires hand-built node blueprints — this skill is the catalog. To enumerate nodes/instances/usages across a **scope** (a whole project, module, model, or repository) rather than navigating from one root, add the `jetbrains.mps.lang.smodel.query` language — it supplies `#instances` / `#usages` / `#nodes` / `#references` / `#models` / `#modules` and a `with () { … }` wrapper, the same queries the MPS Console runs. Its results compose with the `smodel`/`collections`/`closures` operations catalogued here. See the `mps-console` skill. ## Critical Directives - **Node equality uses `:eq:` and `:ne:`**, never `==` or `.equals()`. Use `NPEEqualsExpression` / `NPENotEqualsExpression`. See `references/node-equality.md`. - **Every `InferredClosureParameterDeclaration` needs a `type` child**, even though MPS infers the type. Use `jetbrains.mps.baseLanguage.structure.UndefinedType` as placeholder. Omitting it cascades into misleading "different parameter numbers" / "out of search scope" / "operation is not applicable to null" errors. See `references/closures-catalog.md`. - **The Java parser cannot produce smodel/collection types** in method return types, cannot parse `:Concept` casts, `.link` accesses, `.behaviorMethod()` calls, or `MetaAdapterFactory.getContainmentLink` inline. Use `LINKS.xxx`/`CONCEPTS.xxx` constants and replace types post-parse. See `references/java-parser-capabilities.md`. - **Mutations need `command { … }`, reads from non-UI code need `read action { … }`**. There is no separate "write action". Behavior methods and rule bodies already hold the right lock. See `references/concurrent-access.md`. - **Pick the right cardinality**: `SLinkAccess` for `0..1` / `1`; `SLinkListAccess` for `0..n` / `1..n`. One pair serves both reference links and containment children (there is no `SChildAccess`/`SChildListAccess`). Wrong choice triggers "out of search scope" / "access to link X is not expected here". See `references/dot-expression-basics.md`. - **`foreach` has two concepts**: collections `ForEachStatement` for `sequence`/`list`/`set`, BaseLanguage `ForeachStatement` for Java arrays/iterables. Wrong choice → type error. See `references/foreach-statements.md`. - **Used-language imports**: NF_* operations require `jetbrains.mps.lang.actions` in the model's used languages; without it, `add new initialized(...)` etc. fail. See `references/property-and-mutation-ops.md` and `references/openapi-and-dependencies.md`. - **Never recommend deprecated operations**: `.role` (use `.containingLink`), `.linkDeclaration` (use `.link`), `.role` on `SReference` (use `.link.name`), `.concept` `Node_GetConceptOperation` (use `node.concept` via typesystem). ## Common-path workflow 1. **Identify the source-of-truth layer**. If the change is to existing logic in a rule/method body, inspect the current node (shallow `mps_mcp_print_node`) before editing. 2. **Prefer `parse_java_and_insert`** for plain Java method bodies, expression replacements, and field declarations on `LINKS`/`CONCEPTS` inner classes. See `references/java-parser-capabilities.md`. 3. **For smodel/collections/closures constructs not parseable as Java**, build the node blueprint by hand. See: - `references/dot-expression-basics.md` — the universal `DotExpression(operand, operation)` chaining pattern, closure literal blueprint, type-cast wrapping rules. - `references/property-and-mutation-ops.md` — property reads/writes, `add new(C)`, `replace with new(C)`, sibling inserts. - `references/references-and-queries.md` — `.ancestor`, `.descendants`, `.reference/C:role/`, `.target`, `.isInstanceOf`, sibling queries. - `references/attribute-access.md` — the `.@` operator: read/set/remove an attribute (annotation) attached to a node and reach the children/refs/properties it grafts on (generator macros, comments, requirement traces). 4. **For variable declarations and method return types** of MPS collection / smodel types, build the type child explicitly — `parse_java_and_insert` produces a wrong `ClassifierType` for these in return-type position. See `references/variable-declarations.md`. 5. **Validate** with `mps_mcp_check_root_node_problems(nodeReference, onlyNodesWithProblems=true)`. Re-read generated `source_gen/...java` only to confirm runtime shape — never to apply fixes. See `references/workflows.md`. 6. **If imports/dependencies break**, add a used language or model dependency via `mps_mcp_model_used_language` / `mps_mcp_model_dependency` / `mps_mcp_module_dependency`. See `references/openapi-and-dependencies.md`. If MPS MCP tools are unavailable, do not hand-edit serialized `.mps` files unless explicitly requested — inspect only and report. ## Related Skills - `mps-baselanguage` — host BaseLanguage statements, expressions, classes; this skill is the smodel/collections/closures overlay. - `mps-quotations` — `<` … `>` quotations and antiquotations for assembling node trees inline; use instead of long blueprint chains where they apply. - `mps-aspect-behavior` — per-concept method authoring; behavior bodies are the most common host for this skill. - `mps-aspect-generator` — generator query bodies, `$IF$`/`$MAP_SRC$.mapperFunction`, where this skill provides the smodel idioms. - `mps-aspect-typesystem` — inference and checking rule bodies; uses the same idioms. - `mps-aspect-constraints` — `getScope`, `canBe*`, property validators; same idiom set. - `mps-node-editing` — programmatic node creation and editing from outside model code (the MCP-tool side rather than smodel-language side). - `mps-console` — the MPS Console and the `jetbrains.mps.lang.smodel.query` language (`with`-statement, `#instances`/`#usages`/`#nodes`/`#models`/`#modules`, scopes); use it to run or generate the smodel code in this skill across a project/repository scope, or to insert console commands via `mps_mcp_insert_console_command_from_json`. ## Reference Index - `references/golden-rules-and-pitfalls.md` — read first when an error looks weird (cascade `UnknownDotCall`, "out of search scope", "different parameter numbers", `List` vs `sequence>`); collected symptom→cause→fix table. - `references/java-parser-capabilities.md` — open before calling `mps_mcp_parse_java_and_insert`. Lists what the parser handles, what it silently mis-types, and the canonical workarounds (LINKS/CONCEPTS pattern, post-parse `replace_node_child`, signature widening to avoid smodel casts in arguments). - `references/workflows.md` — step-by-step recipes: adding a new helper method to a checking-rule class, replacing an expression inside a rule body, interacting with `source_gen/` artifacts. - `references/concept-id-table.md` — `MetaAdapterFactory` hex IDs for BaseLanguage concepts and links (`ThrowStatement`, `CatchClause`, `TryCatchStatement`, `VariableReference`, etc.) plus persistent node refs for `Type`, `Expression`, `Classifier`, `SequenceType`, `ListType`, `SNodeType`. - `references/smodel-concepts-catalog.md` — every smodel concept (`SNodeType`, `SLinkAccess`, `Node_GetAncestorOperation`, `OfConceptOperation`, `Concept_*Operation`, `EnumMember_*`, …) with its ID and MPS surface notation. Open when you need to pick a concept and don't remember which one. - `references/baselanguage-key-concepts.md` — the small set of BaseLanguage concepts that this skill keeps reaching for (`DotExpression`, `ForeachStatement`, `BlockStatement`, `NPE*Expression`, `UndefinedType`). - `references/concurrent-access.md` — `command`, `read action`, `execute command in EDT`, `undo-transparent command`. Open when writing code that reads/mutates models outside a rule or behavior body. - `references/collections-catalog.md` — every `*Operation` from `jetbrains.mps.baseLanguage.collections` (`where`/`select`/`translate`/`any`/`take`/`sortBy`/`reduceLeft`/`toList`/…), the type hierarchy (`sequence` ⊃ `list`/`set`; `map`), creator concepts, list/set/map mutators, `iterator` vs `modifying_iterator`, sorted variants, lazy-vs-eager rule, and the `isEmpty`/`isNotEmpty` collections-vs-baselanguage ambiguity. - `references/closures-catalog.md` — `ClosureLiteral` parameters/body shape, `InferredClosureParameterDeclaration` requirements, `FunctionType`, `InvokeFunctionOperation` vs `InvokeExpression` (recursion), `YieldStatement`, SAM conversion, generated-Java compilation form, runtime jar dependency. - `references/dot-expression-basics.md` — the universal `DotExpression(operand, operation)` chaining pattern; closure-literal blueprint (the reusable building block); cardinality cheat-sheet (`SLinkAccess` vs `SLinkListAccess`, one pair for both references and children); when to wrap an operand in `SNodeTypeCastExpression`; navigation blueprints (`.link`, `.parent`, `.children`, `.ancestor`, `.ancestors`, `.descendants` including `+` include-self form); `node:C` vs `node as C`; `expr/` (`SemanticDowncastExpression`) and `downcast expr` (`DowncastExpression`) for crossing into Java APIs; `.isInstanceOf` / `.isNotNull` / `.isNull` / `.behaviorMethod(args)`; `where` / `any` / `translate` / `list.add` blueprints. - `references/property-and-mutation-ops.md` — read for property reads/writes (`SPropertyAccess`, assignment, `Property_RemoveOperation`) and tree mutations (`SNodeCreator`, `add new(C)`, `set new(C)`, `replace with new(C)` / `replace with(other)`, `.copy`, `.detach`, sibling inserts), including all `NF_*` factory-initialized variants and the required `jetbrains.mps.lang.actions` used-language import. - `references/references-and-queries.md` — `Node_GetReferenceOperation` (`.reference/C:role/`), `Node_GetReferencesOperation`, `Reference_GetTargetOperation` etc.; plus query operations `.siblings`/`.next-sibling`/`.prev-sibling*`, `.containingRoot`/`.containingLink`/`.model`/`.index`, `.isExactly(C)`, `seq.ofConcept`, `seq.ofAspect`, enum-member operations. - `references/attribute-access.md` — the `.@` operator (`AttributeAccess` + `NodeAttributeQualifier` / `LinkAttributeQualifier` / `ChildAttributeQualifier` / `PropertyAttributeQualifier` / `AllAttributeQualifier`): read, attach/replace (assignable l-value), or remove an attribute, list semantics of `multiple` attributes (`.@role.add(...)`), and chain into the children/refs/properties it grafts onto a node. Pairs with `mps-aspect-structure-concepts/references/attributes-and-annotations.md` (the structure side). - `references/link-and-concept-literals.md` — standalone `link/C : role/` (`LinkIdRefExpression`, two required refs) and `concept/C/` (`ConceptIdRefExpression`). Open when an API needs an `SContainmentLink`/`SReferenceLink`/`SConcept` argument with no preceding `node.` operand; covers the distinction from `OperationParm_LinkQualifier` and `RefConcept_Reference`. - `references/foreach-statements.md` — the two `foreach` concepts (collections `ForEachStatement` + `ForEachVariable` / `ForEachVariableReference` vs BaseLanguage `ForeachStatement` + `LocalVariableDeclaration` / `VariableReference`). Open when iterating produces a typesystem error or when you need to reference the loop variable. - `references/node-equality.md` — `NPEEqualsExpression` (`:eq:`) and `NPENotEqualsExpression` (`:ne:`) blueprints and when to use them. - `references/variable-declarations.md` — type-child choices for locals and return types (`node`, `nlist`, `node-ptr`, `concept`, `search scope`, `enummember`, `sequence/list/set>`, `boolean`); creator blueprints for `new arraylist>` / `new hashset>` / etc.; the parse-time return-type fix-up blueprints for `sequence>` and `list>`. - `references/openapi-and-dependencies.md` — `org.jetbrains.mps.openapi.*` interfaces and threading rules (when hand-written Java calls into models); module dependencies vs model dependencies vs used languages, with failure modes ("Concept not imported", "cannot resolve", "Class not found at runtime") and the matching MCP tool to call.