foldSchedule - API reference

API reference › @evolu/common › Schedule › foldSchedule

function foldSchedule<Z, Output>(
  initial: Z,
  f: (acc: Z, output: Output) => Z,
): <Input>(schedule: Schedule<Output, Input>) => Schedule<Z, Input>;

Defined in: packages/common/src/Schedule.ts:1064

Folds over the outputs of a schedule, accumulating state.

Each step outputs the accumulated value. Useful for tracking totals, collecting outputs, or building up metadata across attempts.

Example

// Track total delay spent
const withTotal = foldSchedule(
  0,
  (total: number, delay: Millis) => total + delay,
)(exponential("100ms"));
// Outputs: 100, 300, 700, 1500, ... (cumulative)

// Collect all outputs
const collected = foldSchedule([] as Millis[], (acc, delay: Millis) => [
  ...acc,
  delay,
])(take(3)(spaced("1s")));
// Outputs: [1000], [1000, 1000], [1000, 1000, 1000]

// Count attempts with custom output
const counted = foldSchedule(
  { attempts: 0, lastDelay: 0 as Millis },
  (acc, delay: Millis) => ({
    attempts: acc.attempts + 1,
    lastDelay: delay,
  }),
)(exponential("100ms"));