mps-aspect-dataflow

name	mps-aspect-dataflow
description	Use when defining or debugging MPS dataflow builders for a concept — control/data flow declarations that drive reachability analysis and variable-use checking. Covers DataFlowBuilderDeclaration, BuilderBlock, emit instructions (code for, jump, ifjump, label, read, write, ret, mayBeUnreachable), positions (AfterPosition, BeforePosition, LabelPosition), the jetbrains.mps.lang.dataFlow language, the NodeParameter implicit, BL+smodel usage inside builder bodies, and IBuilderMode for advanced analyses such as nullable/non-null tracking.
type	reference

MPS Dataflow Aspect

The dataflow aspect (jetbrains.mps.lang.dataFlow, l:7fa12e9c-b949-4976-b4fa-19accbc320b4) lets a language describe how control and data flow through nodes of a concept. MPS uses that information for reachability analysis, uninitialised-variable checks, and (via IBuilderMode) richer flow analyses such as nullable tracking.

Mental Model

Each DataFlowBuilderDeclaration answers: given a node of concept X, in what order might execution visit its children, and which variables are read or written?

The builder body is a BL StatementList (inside a BuilderBlock). You use normal BL control flow (if, foreach, local variables) to compute which emit instructions to output at runtime. The node implicit parameter (concept NodeParameter) is always in scope — its type is the concept referenced by conceptDeclaration, giving smodel-typed access to children and references.

The MPS dataflow engine builds a control-flow graph from the emitted instructions, then runs analyses (unreachable code, uninitialised variable reads) on that graph. The engine only traces the paths you declare; if no builder exists for a concept, MPS falls back to delegating all children in declaration order.