prefer-traverse.md

Replace map + sequence with traverse (fp-ts/prefer-traverse)

Suggest replacing the combination of map (or mapWithIndex) followed by sequence with traverse (or traverseWithIndex).

💡 Fixable: This rule provides in-editor suggested fixes.

Rule Details

Examples of incorrect code for this rule:

import { pipe } from "fp-ts/pipeable";
import { map, sequence } from "fp-ts/Array";
import { option, some } from "fp-ts/Option";

pipe(
  [1, 2, 3],
  map((n) => some(n)),
  sequence(option)
);

import { pipe } from "fp-ts/pipeable";
import { mapWithIndex, sequence } from "fp-ts/Array";
import { option, some } from "fp-ts/Option";

pipe(
  [1, 2, 3],
  mapWithIndex((i) => some(i)),
  sequence(option)
);

Examples of correct code for this rule:

import { pipe } from "fp-ts/pipeable";
import { traverse } from "fp-ts/Array";
import { option, some } from "fp-ts/Option";

pipe(
  [1, 2, 3],
  traverse(option)((n) => some(n))
);

import { pipe } from "fp-ts/pipeable";
import { traverseWithIndex } from "fp-ts/Array";
import { option, some } from "fp-ts/Option";

pipe(
  [1, 2, 3],
  traverseWithIndex(option)((i) => some(i))
);