Effect CommunityEC
Effect Community•2y ago
BinaryArtifex

Understanding Complex TypeScript Signatures: A Guide for Beginners

it'd be good if someone could write an article or at the least take me through how they interpret heavy type signatures in their own mental model. i see a lot of responses where a type or interface is just slapped down that looks something like the tap type below. what amazes me more is folks asking the question are all 'aha! i see now'. wtf? I see that level of hieroglyphics and my brain up and shits itself and defaults to repeats of funny cat videos. I think gleaning a little insight into how some of the effect ninjas here break down advanced types like this and actually understand whats going on would be invaluable.

export const tap: {
  <A, X>(
    f: (a: NoInfer<A>) => X
  ): <E, R>(
    self: Effect<A, E, R>
  ) => [X] extends [Effect<infer _A1, infer E1, infer R1>] ? Effect<A, E | E1, R | R1>
    : [X] extends [PromiseLike<infer _A1>] ? Effect<A, E | Cause.UnknownException, R>
    : Effect<A, E, R>
  <X>(
    f: NotFunction<X>
  ): <A, E, R>(
    self: Effect<A, E, R>
  ) => [X] extends [Effect<infer _A1, infer E1, infer R1>] ? Effect<A, E | E1, R | R1>
    : [X] extends [PromiseLike<infer _A1>] ? Effect<A, E | Cause.UnknownException, R>
    : Effect<A, E, R>
  <A, E, R, X>(
    self: Effect<A, E, R>,
    f: (a: NoInfer<A>) => X
  ): [X] extends [Effect<infer _A1, infer E1, infer R1>] ? Effect<A, E | E1, R | R1>
    : [X] extends [PromiseLike<infer _A1>] ? Effect<A, E | Cause.UnknownException, R>
    : Effect<A, E, R>
  <A, E, R, X>(
    self: Effect<A, E, R>,
    f: NotFunction<X>
  ): [X] extends [Effect<infer _A1, infer E1, infer R1>] ? Effect<A, E | E1, R | R1>
    : [X] extends [PromiseLike<infer _A1>] ? Effect<A, E | Cause.UnknownException, R>
    : Effect<A, E, R>
}
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