Glossary

Area A namespace unit in Mélodium, materialized by a .mel file. Subareas are created by placing .mel files inside a folder with the parent area’s name. Elements within the same project are referenced using root/area::element or local/subarea::element. See: Project Organization

Block A port kind written Block<T> that carries exactly one value of type T. Used for single events, triggers, and configuration values. The name refers to a single block of data, not to suspending execution. See: Connections

Configuration parameter A parameter written in square brackets ([param: Type]) on a treatment declaration, used to pass a model instance or fixed resource into a treatment. Configuration parameters are always constant. See: Parameters

Connection A directed link from an output port to an input port, written with ->. Connections define the data flow between treatment instances inside a treatment body. A connection must link ports of the same type and kind, cannot create cycles, and a given input may only have one connection. See: Connections

Context Track-wide data prefixed with @, provided by a source treatment and implicitly available to any treatment in the same track that declares require @ContextName. Unlike parameters, contexts do not need to be explicitly passed down the call chain. See: Contexts

Entrypoint A named treatment that can be invoked directly from the command line to start a program. Declared in Compo.toml. The main entrypoint is called when no name is given. Treatment parameters become CLI arguments automatically. See: Entrypoints

Function A pure, side-effect-free callable prefixed with |, used to compute parameter values. Functions are executed once at program initialization when used as const parameters, or once per track creation when used as var parameters. See: Functions

Locator A string telling where the value of a secret is read from when revealed, written <scheme>:<path>, such as env:MELODIUM_SECRET_DB_PASSWORD, file:/run/secrets/token or vault:kv/data/app#password. See: Secrets

Model A stateful element that lives for the entire program execution. Models are the sources of events and tracks: they are the starting points from which data enters the system. A model is declared by extending a library model and configuring its parameters. See: Models

Secret A value of type Secret<T> holding a password, token or key. It holds where its value comes from, and only the elements using the value reveal it, so the value never appears in parameters, logs, debug files or reports. See: Secrets

Self A keyword used inside a treatment body to refer to the hosting treatment’s own input and output ports. Self.input_name and Self.output_name wire the treatment’s declared ports into its internal connection graph. See: Treatments

Stream A port kind written Stream<T> that carries a continuous, unbounded sequence of values of type T. The general case for data transmission in Mélodium. See: Connections

Track The complete set of treatment instances and connections created together from a single model event. Each event from a model spawns a new independent track. All tracks run concurrently, each with its own data and context. See: Tracks

Trait An intrinsic capability of a type, such as the ability to be added (Add), compared (PartialEquality), or converted to a string (ToString). Traits are used to constrain generic type parameters. See: Traits

Treatment The primary computation unit in Mélodium. A treatment declares inputs, outputs, and a body of other treatment instances connected together. Treatments do not execute line by line; all inner treatments run concurrently when data is available. See: Treatments

void A core type that carries no value. Block<void> is used as a trigger (signals that something happened), and Stream<void> is used as a continuation indicator (signals ongoing activity without conveying data). See: Core types