Series Accumulator

Turns what is true now into what was true then.

Built from a real problem: someone making an event-price app could not obtain historical ticket prices. The data was public every day and archived by nobody, so the only way to have last month's prices was to have been collecting last month.

The engine is one decision that is easy to get wrong in a way nothing reports: STORE TRANSITIONS, NOT POLLS. The obvious implementation appends a row per poll, and a thousand prices every ten minutes is 144,000 rows a day to say almost nothing changed. Storing transitions means a year of a stable price is one row, and the series stays queryable at any point in time.

This is the shape of every accumulation dataset: cheap to hold, impossible to backfill, worth nothing if you start next year.

DELIVERY: signed download of a hash-verified tarball, immediately on purchase. Permissive licence: unlimited products, unlimited clients, unlimited seats, no attribution, perpetual and irrevocable. One restriction, do not republish the source as source.

Interface

What you call, and what comes back. Types and signatures only — the implementation ships with the source.

  export const centsEqual = (a: number | null, b: number | null): boolean;
  export const looseStringEqual = (a: string | null, b: string | null): boolean;