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Branching

branch routes a tagged union to different handlers based on its kind discriminant. Each case handler receives the unwrapped payload — not the full { kind, value } wrapper.

Basic branching​

From demos/convert-folder-to-ts/handlers/type-check-fix.ts:

export const typeCheckFix = loop((recur) =>
  typeCheck.then(classifyErrors).branch({
    HasErrors: Iterator.fromArray<TypeError>().map(fix).drop().then(recur),
    Clean: drop,
  }),
);

classifyErrors returns a tagged union — either { kind: "HasErrors", value: TypeError[] } or { kind: "Clean", value: void }. The HasErrors handler receives the TypeError[] of errors directly; the Clean handler receives void.

Branching with Result types​

Result combinators like .unwrapOr() are built on branch internally. You can also branch on Results explicitly:

riskyStep.branch({
  Ok: processSuccess,
  Err: handleFailure,
})

Branching with Option types​

The same pattern works for Option<T>:

maybeFind.branch({
  Some: processFound,
  None: constant("not found"),
})