Enhance sum type workflow (Data.taggedEnum)

[peterreisz]

What is the problem this feature would solve?

Working with sum types (tagged unions) must be cheap to easily create models which prevents storing impossible states inside them. I suggest adding new helpers for Data.taggedEnum:

• $match non-exhaustive support
• $get
• $map

What is the feature you are proposing to solve the problem?

import { Data } from "effect"
 
type RemoteData = Data.TaggedEnum<{
  Loading: {}
  Success: { readonly data: string }
  Failure: { readonly reason: string }
}>
 
const { $is, $match, $get, $map, Loading, Success, Failure } =
  Data.taggedEnum<RemoteData>()

// Non exhaustive matcher: (RemoteData) -> Option<_>
const matcher = $match({
  Success: ({ data }) => `this is a Success: ${data}`,
  Failure: ({ reason }) => `this is a Failure: ${reason}`
})

// Getter: (tag) => (state) => Option<Variant>
const maybeSuccess = $get('Success')(Loading()) 

// Map: (tag) => ((singleState) => newState) => (state) => computedState
const singleMapper = $map('Success')(({ data }) => ({ foo: data }))

// Map: ({Variant: (singleState) => newState}) => (state) => computedState
const multiMapper = $map({
  Success: () => { foo: 'bar' },
  Loading: () => { other: 42 },
  // Missing Failure leaves it the same
})

What alternatives have you considered?

Manual implementation.

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Willing to send a PR in case of you like my suggestions.