The type for JavaScript promises.

create (fun res rej -> ...) is a promise that can be resolved with res and rejected with rej. Note that res has a weird semantics see resolve for details.

resolve v is a promise that resolve with v. Warning. this is not a monadic return it also joins. Use Fut for a sound typed semantics of promises.

reject v is a promise that rejects with v.

await p k waits for p to resolve and continues with k.

bind p fn binds p's resolution to function fn.

then' p res rej binds p's resolution to res and p's rejection to rej.

all arr is a promise that resolves all the promises in the array arr to an array of values.