Iterable.intersperse — API

Iterable.intersperseconsteffect/Iterable.ts:999

<B>(middle: B): <A>(self: Iterable<A>) => Iterable<A | B>
<A, B>(self: Iterable<A>, middle: B): Iterable<A | B>

Places a separator between members of an Iterable.

When to use

Use to lazily insert a separator between adjacent values.

Details

If the input is a non-empty array, the result is also a non-empty array.

Example (Interspersing separators)

import { Iterable } from "effect"

// Join numbers with separator
const numbers = [1, 2, 3, 4]
const withCommas = Iterable.intersperse(numbers, ",")
console.log(Array.from(withCommas)) // [1, ",", 2, ",", 3, ",", 4]

// Join words with spaces
const words = ["hello", "world", "from", "effect"]
const sentence = Iterable.intersperse(words, " ")
console.log(Array.from(sentence).join("")) // "hello world from effect"

// Empty iterable remains empty
const empty = Iterable.empty<string>()
const stillEmpty = Iterable.intersperse(empty, "-")
console.log(Array.from(stillEmpty)) // []

// Single element has no separators added
const single = [42]
const noSeparator = Iterable.intersperse(single, "|")
console.log(Array.from(noSeparator)) // [42]

// Build CSS-like strings
const styles = ["color: red", "font-size: 14px", "margin: 10px"]
const css = Iterable.intersperse(styles, "; ")
console.log(Array.from(css).join("")) // "color: red; font-size: 14px; margin: 10px"

combining

Source effect/Iterable.ts:99924 lines

export const intersperse: {
  <B>(middle: B): <A>(self: Iterable<A>) => Iterable<A | B>
  <A, B>(self: Iterable<A>, middle: B): Iterable<A | B>
} = dual(2, <A, B>(self: Iterable<A>, middle: B): Iterable<A | B> => ({
  [Symbol.iterator]() {
    const iterator = self[Symbol.iterator]()
    let next = iterator.next()
    let emitted = false
    return {
      next() {
        if (next.done) {
          return next
        } else if (emitted) {
          emitted = false
          return { done: false, value: middle }
        }
        emitted = true
        const result = next
        next = iterator.next()
        return result
      }
    }
  }
}))