Glossary

Reference. Short definitions of the terms used throughout the documentation. Each links to the page that explains it in depth.

Result<T, E> : A discriminated union of three runtime states — Ok<T>, Err<E>, Defect — intersected with the fluent method surface. E names only the anticipated domain failures. See Result & AsyncResult surface.

AsyncResult<T, E> : The asynchronous counterpart of Result<T, E>, typed as Awaitable<Result<T, E>>. Its internal promise never rejects; await collapses it to a Result. See The async model.

Ok : The success variant of a Result, carrying a value of type T.

Err : The modeled failure variant, carrying an error of type E. An Err is an anticipated outcome your callers are expected to handle.

Defect : The unmodeled failure variant — a bug, a panic, an un-triaged rejection. It is invisible to the type (never appears in E) and can only be observed by match, recoverDefect, or the tapDefect / tapFailure observers. See The Defect Channel.

qualify : The mandatory function passed to fromPromise / fromThrowable that triages each raw failure into a modeled error (which enters E) or defect(cause) (which does not). It is synchronous, and its Defect arm is subtracted from E. See Qualification.

defect (the helper) : A helper injected at every triage site — inside qualify and in each error-match branch — that marks a cause as unmodeled. It is never imported; there is no public Defect constructor.

panic : What get / getErr / the getOr* family do on a Defect: they rethrow the original cause with its original stack, rather than recovering it. never on the error channel means the modeled channel is empty, not that get() cannot throw. See The Defect Channel.

tagged error : The recommended error convention — a class extending Error with a _tag discriminant, built with TaggedError(tag). Core Result stays generic in E; only the tag-aware utilities require E extends { _tag: string }. See Model errors.

matcher : The built-in match(error) builder handed to every error combinator's callback. You return it un-terminated; the combinator runs .exhaustive(), so a missing case does not compile. See Exhaustive error matching.

P / P.tag(t) : P is unthrown's pattern namespace (P._, P.tag, P.instanceOf, P.when, P.union, P.string, P.number). P.tag(t) is sugar for the { _tag: t } pattern, narrowing to a tagged variant and its payload — the everyday way to write an arm. P._ is the universal catch-all; it makes any match exhaustive, so it is reserved for the two cases enumeration cannot express — a helper generic in E, or an E that is a single type rather than a union of cases — rather than used as a default. See Exhaustive error matching.

Awaitable<R> : A success-only thenable type — resolves to R, models no rejection channel. AsyncResult<T, E> is Awaitable<Result<T, E>>.

boundary : An edge of your program where untyped failure enters — a throwing function, a rejecting promise, a nullable API. Each is crossed with a from* constructor that forces qualification. See Qualify a boundary.

combinator : Any method on the fluent surface (map, flatMap, mapErrCases, tap, …) that transforms or observes a channel and returns another Result / AsyncResult. A throw inside a combinator becomes a Defect.

eliminator : A method that leaves the Result world — match, get / getErr, and the getOr* family — folding or extracting a plain value.