Nested Effects (from promises)

Hi all
I am new to effect.ts and trying to figure out how to two possible paths following a promise in an idiomatic way. My goal would be to have a pipeline of first a fetch request and then split the result on the

Response.ok

Response.ok

boolean (true =>

Success

Success

; false =>

Failure

Failure

). Then based on the outcome, I want the

Response.json()

Response.json()

in the success case, and the

Response.text()

Response.text()

in a failure case. I would expect it to have the type of

Effect.Effect<unknown, string, never>

Effect.Effect<unknown, string, never>

at the end.

This is my current draft, which does result in

Effect.Effect<Effect.Effect<unknown, never, never>, Effect.Effect<never, string, never>, never>

Effect.Effect<Effect.Effect<unknown, never, never>, Effect.Effect<never, string, never>, never>

const program = pipe(
  Effect.promise(() => fetch("some-url")),
  Effect.filterOrFail(
    (response) => response.ok,
    Function.identity,
  ),
  Effect.mapBoth({
    onSuccess: (response) => Effect.promise(() => response.json() as Promise<unknown>),
    onFailure: (response) => Effect.promise(() => response.text()),
  }),
);

const program = pipe(
  Effect.promise(() => fetch("some-url")),
  Effect.filterOrFail(
    (response) => response.ok,
    Function.identity,
  ),
  Effect.mapBoth({
    onSuccess: (response) => Effect.promise(() => response.json() as Promise<unknown>),
    onFailure: (response) => Effect.promise(() => response.text()),
  }),
);

Is there a eleganter way to achieve this? Or are there some helper functions in the library which unwrap this in the way I would like it? Thank you for any help or explanation.

Effect Community•2y ago

Oliver Bucher

Nested Effects (from promises)

Response.ok

Response.ok

boolean (true =>

Success

Success

; false =>

Failure

Failure

). Then based on the outcome, I want the

Response.json()

Response.json()

in the success case, and the

Response.text()

Response.text()

in a failure case. I would expect it to have the type of

Effect.Effect<unknown, string, never>

Effect.Effect<unknown, string, never>

at the end.

This is my current draft, which does result in

Effect.Effect<Effect.Effect<unknown, never, never>, Effect.Effect<never, string, never>, never>

Effect.Effect<Effect.Effect<unknown, never, never>, Effect.Effect<never, string, never>, never>

const program = pipe(
  Effect.promise(() => fetch("some-url")),
  Effect.filterOrFail(
    (response) => response.ok,
    Function.identity,
  ),
  Effect.mapBoth({
    onSuccess: (response) => Effect.promise(() => response.json() as Promise<unknown>),
    onFailure: (response) => Effect.promise(() => response.text()),
  }),
);

const program = pipe(
  Effect.promise(() => fetch("some-url")),
  Effect.filterOrFail(
    (response) => response.ok,
    Function.identity,
  ),
  Effect.mapBoth({
    onSuccess: (response) => Effect.promise(() => response.json() as Promise<unknown>),
    onFailure: (response) => Effect.promise(() => response.text()),
  }),
);

Is there a eleganter way to achieve this? Or are there some helper functions in the library which unwrap this in the way I would like it? Thank you for any help or explanation.

Nested Effects (from promises)

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