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docs: Clarify Option + andThen guidance in pipeline docs #1295

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2 changes: 1 addition & 1 deletion content/src/content/docs/docs/data-types/option.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -484,7 +484,7 @@ const fetchData = (): Effect.Effect<string, string> => {
: Effect.fail("Failed to fetch data")
}

// Mixing Either and Effect
// Mixing Option and Effect
const program = Effect.all([head([1, 2, 3]), fetchData()])

Effect.runPromise(program).then(console.log)
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37 changes: 7 additions & 30 deletions content/src/content/docs/docs/getting-started/building-pipelines.mdx
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Expand Up @@ -294,9 +294,8 @@ const result2 = pipe(
Effect.runPromise(result2).then(console.log) // Output: 190
```

### Option and Either with andThen

Both [Option](/docs/data-types/option/#interop-with-effect) and [Either](/docs/data-types/either/#interop-with-effect) are commonly used for handling optional or missing values or simple error cases. These types integrate well with `Effect.andThen`. When used with `Effect.andThen`, the operations are categorized as scenarios 5 and 6 (as discussed earlier) because both `Option` and `Either` are treated as effects in this context.
### Option with andThen
[Option](/docs/data-types/option/#interop-with-effect) is commonly used for handling optional or missing values. It integrates well with `Effect.andThen`. When used with `Effect.andThen`, the operations are categorized as scenarios 5 and 6 (as discussed earlier) because both `Option` is treated as effect in this context.

**Example** (with Option)

Expand All @@ -322,35 +321,13 @@ This is because `Option<A>` is treated as an effect of type `Effect<A, NoSuchEle
A value of type `Option<A>` is interpreted as an effect of type `Effect<A, NoSuchElementException>`.
</Aside>

**Example** (with Either)

```ts twoslash
import { pipe, Effect, Either } from "effect"

// Function to parse an integer from a string that can fail
const parseInteger = (input: string): Either.Either<number, string> =>
isNaN(parseInt(input))
? Either.left("Invalid integer")
: Either.right(parseInt(input))

// Simulated asynchronous task fetching a string from database
const fetchStringValue = Effect.tryPromise(() => Promise.resolve("42"))

// ┌─── Effect<number, string | UnknownException, never>
// ▼
const program = pipe(
fetchStringValue,
Effect.andThen((str) => parseInteger(str))
)
```

Although one might expect the type of `program` to be `Effect<Either<number, string>, UnknownException, never>`, it is actually `Effect<number, string | UnknownException, never>`.
[Either](/docs/data-types/either/#interop-with-effect) also interoperates with `Effect.andThen`, but in Effect applications it is usually better to:

This is because `Either<A, E>` is treated as an effect of type `Effect<A, E>`, meaning the errors are combined into a union type.
- use `Option` for absence/presence
- use `Effect` failures for domain errors
- use `Exit` when you need the full result of running an effect (including rich failure causes)

<Aside type="tip" title="Either As Effect">
A value of type `Either<A, E>` is interpreted as an effect of type `Effect<A, E>`.
</Aside>
`Either` is still useful as a small discriminated union, especially at boundaries (for example adapters to external APIs), but it is not the default recommendation for core Effect pipeline modeling.

## tap

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