Prelude.res

A set of basic functions extending the Js and/or Belt modules.

Prelude.PromiseExported

Includes all the functions of Js.Promise2 (since 5.0) and adds:

type t<+'a> = promise<'a>

Note: Since promises are everywhere in browser code, most of the functions in this module are always included in Prelude. So open Prelude is enough to access the most common functions. This might change in a future (or final release of 5.0.0) because of the new async/await syntax in ReScript 10.1.

thenResolve: (promise<'a>, 'a => 'b) => promise<'b>

Takes a fn function and maps the resolved value.

Since ReScript 10.1 we expect this function to become less and less useful because

promise->thenResolve(fn)

is the same as

fn(await promise)

catchResolve: (promise<'a>, error => 'a): promise<'a>

Similar to thenResolve but using catch. This is useful to turn errors into values.

rejectWithError: exn => promise<result<'a, error>>

takes an exception an returns a promise that rejects with Error(Js.Promise2.error)

finally: (promise<'a>, 'a => unit) => promise<'a>

Binding to JavaScript's finally.

thenDo: (promise<'a>, 'a => unit) => unit

Executes a function when the promise resolves; return the unit value ().

Prelude.Promises

Includes all the functions from module PromiseExported but those are not exported. Notice the name is Promises (plural form), to avoid clashes with the browser's native Promise.

ellapsed: int => promise<unit>

Return a promise that resolve in the given time (in milliseconds). This just wraps Js.Global.setTimeout as a promise.

Note: This function is not included in Prelude.

result: promise<'a> => promise<result<'a, error>>

Converts a promise to another that always resolves to a result; it never rejects, but instead resolves to an Error.

Note: These functions are not included in Prelude.

iter: array<unit => 'a> => promise<array<'a>>

This similar to Promises.all, but we execute the functions iteratively.

Prelude.PromisedResult

This module provides functions to the type

type t<'a, 'e> = promise<result<'a, 'e>>

In the following will use the alias t<'a, 'e> instead of the longer type promise<result<'a, 'e>>.

map: (t<'a, 'e>, 'a => 'b) => t<'b, 'e>

mapWithDefault: (t<'a, 'e>, 'b, 'a => 'b) => promise<'b>

flatMap: (t<'a, 'e>, 'a => result<'b, 'e>) => t<'b, 'e>

mapError: (t<'a, 'e>, 'e => 'c) => t<'a, 'c>

flatMapError: (t<'a, 'e>, 'e => result<'a, 'c>) => t<'a, 'c>

bind: (t<'a, 'e>, 'a => t<'b, 'e>) => t<'b, 'e>

flip: t<'a, 'e> => t<'e, 'a>

Flip Ok to Error, and Error to Ok.

ok: t<'a, 'e> => promise<option<'a>>

Convert a promise resolving to result, to one that resolves to an option discarding Errors.

warn: t<'a, 'e> => promise<option<'a>>

Convert a promise resolving to result, to one that resolves to an option discarding Errors, but issuing a console warning.

scream: t<'a, 'e> => promise<option<'a>>

Convert a promise resolving to result, to one that resolves to an option discarding Errors, but issuing a console error.

bail: array<unit => t<'a, 'e>> => t<array<'a>, 'e>

Run each function in turn until one resolves to an Error, or all resolve to Ok. Return Ok(results) with the collected results or the first Error.

chain: ('a, array<'a => t<'a, 'e>>) => t<'a, 'e>

Run each function in turn passing each Ok result to the next function. Stop as soon as a function returns Error.

untilOk: array<unit => t<'a, 'e>> => t<option<'a>, 'e>

Execute the actions one by one and resolve to the first Ok result, if no action returns Ok, resolve to the last Error result.

The only case where this resolves to None is when actions is the empty array.