StateReaderTaskEither.traverseArray drops state updates between iterations

[bwbuchanan]

🐛 Bug report

Current Behavior

In fp-ts 2.10.2, SRTE.traverseArray does not pass the output state from each step to the subsequent step. Each step receives the initial state. As a result, all state transformations are lost except for the final one.

Expected behavior

In fp-ts 2.9.5, SRTE.traverseArray passes the output state from each step to the subsequent step. This is the expected behavior.

Reproducible example

import * as E from "fp-ts/Either";
import * as SRTE from "fp-ts/StateReaderTaskEither";
import { pipe } from "fp-ts/function";

async function main(): Promise<void> {
  const state = pipe(
    await pipe([1, 2, 3], SRTE.traverseArray(fn))([])({})(),
    E.map(([_, state]) => state),
    E.getOrElseW(() => null)
  );

  console.log(state);
}

function fn(
  v: number
): SRTE.StateReaderTaskEither<ReadonlyArray<number>, {}, Error, void> {
  return SRTE.modify((a) => [...a, v]);
}

main();

2.9.5 prints:

[ 1, 2, 3 ]

2.10.2 prints:

[ 3 ]

Software	Version(s)
fp-ts	2.10.2
TypeScript	4.2.4

[gcanti]

@bwbuchanan thanks for the bug report, patch released.

[bwbuchanan]

@gcanti thanks for the quick fix!