import { Observable } from '../Observable';
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import { SchedulerLike } from '../types';
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export declare type ConditionFunc<S> = (state: S) => boolean;
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export declare type IterateFunc<S> = (state: S) => S;
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export declare type ResultFunc<S, T> = (state: S) => T;
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export interface GenerateBaseOptions<S> {
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/**
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* Initial state.
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*/
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initialState: S;
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/**
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* Condition function that accepts state and returns boolean.
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* When it returns false, the generator stops.
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* If not specified, a generator never stops.
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*/
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condition?: ConditionFunc<S>;
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/**
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* Iterate function that accepts state and returns new state.
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*/
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iterate: IterateFunc<S>;
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/**
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* SchedulerLike to use for generation process.
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* By default, a generator starts immediately.
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*/
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scheduler?: SchedulerLike;
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}
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export interface GenerateOptions<T, S> extends GenerateBaseOptions<S> {
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/**
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* Result selection function that accepts state and returns a value to emit.
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*/
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resultSelector: ResultFunc<S, T>;
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}
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/**
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* Generates an observable sequence by running a state-driven loop
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* producing the sequence's elements, using the specified scheduler
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* to send out observer messages.
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*
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* 
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*
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* @example <caption>Produces sequence of 0, 1, 2, ... 9, then completes.</caption>
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* const res = generate(0, x => x < 10, x => x + 1, x => x);
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*
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* @example <caption>Using asap scheduler, produces sequence of 2, 3, 5, then completes.</caption>
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* const res = generate(1, x => x < 5, x => x * 2, x => x + 1, asap);
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*
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* @see {@link from}
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* @see {@link Observable}
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*
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* @param {S} initialState Initial state.
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* @param {function (state: S): boolean} condition Condition to terminate generation (upon returning false).
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* @param {function (state: S): S} iterate Iteration step function.
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* @param {function (state: S): T} resultSelector Selector function for results produced in the sequence. (deprecated)
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* @param {SchedulerLike} [scheduler] A {@link SchedulerLike} on which to run the generator loop. If not provided, defaults to emit immediately.
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* @returns {Observable<T>} The generated sequence.
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*/
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export declare function generate<T, S>(initialState: S, condition: ConditionFunc<S>, iterate: IterateFunc<S>, resultSelector: ResultFunc<S, T>, scheduler?: SchedulerLike): Observable<T>;
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/**
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* Generates an Observable by running a state-driven loop
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* that emits an element on each iteration.
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*
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* <span class="informal">Use it instead of nexting values in a for loop.</span>
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*
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* <img src="./img/generate.png" width="100%">
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*
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* `generate` allows you to create stream of values generated with a loop very similar to
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* traditional for loop. First argument of `generate` is a beginning value. Second argument
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* is a function that accepts this value and tests if some condition still holds. If it does,
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* loop continues, if not, it stops. Third value is a function which takes previously defined
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* value and modifies it in some way on each iteration. Note how these three parameters
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* are direct equivalents of three expressions in regular for loop: first expression
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* initializes some state (for example numeric index), second tests if loop can make next
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* iteration (for example if index is lower than 10) and third states how defined value
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* will be modified on every step (index will be incremented by one).
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*
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* Return value of a `generate` operator is an Observable that on each loop iteration
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* emits a value. First, condition function is ran. If it returned true, Observable
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* emits currently stored value (initial value at the first iteration) and then updates
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* that value with iterate function. If at some point condition returned false, Observable
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* completes at that moment.
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*
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* Optionally you can pass fourth parameter to `generate` - a result selector function which allows you
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* to immediately map value that would normally be emitted by an Observable.
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*
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* If you find three anonymous functions in `generate` call hard to read, you can provide
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* single object to the operator instead. That object has properties: `initialState`,
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* `condition`, `iterate` and `resultSelector`, which should have respective values that you
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* would normally pass to `generate`. `resultSelector` is still optional, but that form
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* of calling `generate` allows you to omit `condition` as well. If you omit it, that means
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* condition always holds, so output Observable will never complete.
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*
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* Both forms of `generate` can optionally accept a scheduler. In case of multi-parameter call,
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* scheduler simply comes as a last argument (no matter if there is resultSelector
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* function or not). In case of single-parameter call, you can provide it as a
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* `scheduler` property on object passed to the operator. In both cases scheduler decides when
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* next iteration of the loop will happen and therefore when next value will be emitted
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* by the Observable. For example to ensure that each value is pushed to the observer
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* on separate task in event loop, you could use `async` scheduler. Note that
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* by default (when no scheduler is passed) values are simply emitted synchronously.
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*
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*
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* @example <caption>Use with condition and iterate functions.</caption>
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* const generated = generate(0, x => x < 3, x => x + 1);
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*
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* generated.subscribe(
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* value => console.log(value),
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* err => {},
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* () => console.log('Yo!')
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* );
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*
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* // Logs:
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* // 0
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* // 1
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* // 2
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* // "Yo!"
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*
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*
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* @example <caption>Use with condition, iterate and resultSelector functions.</caption>
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* const generated = generate(0, x => x < 3, x => x + 1, x => x * 1000);
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*
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* generated.subscribe(
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* value => console.log(value),
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* err => {},
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* () => console.log('Yo!')
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* );
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*
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* // Logs:
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* // 0
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* // 1000
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* // 2000
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* // "Yo!"
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*
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*
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* @example <caption>Use with options object.</caption>
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* const generated = generate({
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* initialState: 0,
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* condition(value) { return value < 3; },
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* iterate(value) { return value + 1; },
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* resultSelector(value) { return value * 1000; }
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* });
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*
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* generated.subscribe(
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* value => console.log(value),
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* err => {},
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* () => console.log('Yo!')
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* );
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*
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* // Logs:
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* // 0
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* // 1000
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* // 2000
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* // "Yo!"
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*
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* @example <caption>Use options object without condition function.</caption>
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* const generated = generate({
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* initialState: 0,
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* iterate(value) { return value + 1; },
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* resultSelector(value) { return value * 1000; }
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* });
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*
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* generated.subscribe(
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* value => console.log(value),
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* err => {},
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* () => console.log('Yo!') // This will never run.
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* );
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*
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* // Logs:
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* // 0
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* // 1000
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* // 2000
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* // 3000
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* // ...and never stops.
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*
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*
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* @see {@link from}
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* @see {@link index/Observable.create}
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*
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* @param {S} initialState Initial state.
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* @param {function (state: S): boolean} condition Condition to terminate generation (upon returning false).
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* @param {function (state: S): S} iterate Iteration step function.
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* @param {function (state: S): T} [resultSelector] Selector function for results produced in the sequence.
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* @param {Scheduler} [scheduler] A {@link Scheduler} on which to run the generator loop. If not provided, defaults to emitting immediately.
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* @return {Observable<T>} The generated sequence.
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*/
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export declare function generate<S>(initialState: S, condition: ConditionFunc<S>, iterate: IterateFunc<S>, scheduler?: SchedulerLike): Observable<S>;
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/**
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* Generates an observable sequence by running a state-driven loop
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* producing the sequence's elements, using the specified scheduler
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* to send out observer messages.
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* The overload accepts options object that might contain initial state, iterate,
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* condition and scheduler.
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*
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* 
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*
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* @example <caption>Produces sequence of 0, 1, 2, ... 9, then completes.</caption>
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* const res = generate({
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* initialState: 0,
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* condition: x => x < 10,
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* iterate: x => x + 1,
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* });
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*
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* @see {@link from}
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* @see {@link Observable}
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*
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* @param {GenerateBaseOptions<S>} options Object that must contain initialState, iterate and might contain condition and scheduler.
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* @returns {Observable<S>} The generated sequence.
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*/
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export declare function generate<S>(options: GenerateBaseOptions<S>): Observable<S>;
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/**
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* Generates an observable sequence by running a state-driven loop
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* producing the sequence's elements, using the specified scheduler
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* to send out observer messages.
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* The overload accepts options object that might contain initial state, iterate,
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* condition, result selector and scheduler.
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*
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* 
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*
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* @example <caption>Produces sequence of 0, 1, 2, ... 9, then completes.</caption>
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* const res = generate({
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* initialState: 0,
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* condition: x => x < 10,
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* iterate: x => x + 1,
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* resultSelector: x => x,
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* });
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*
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* @see {@link from}
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* @see {@link Observable}
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*
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* @param {GenerateOptions<T, S>} options Object that must contain initialState, iterate, resultSelector and might contain condition and scheduler.
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* @returns {Observable<T>} The generated sequence.
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*/
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export declare function generate<T, S>(options: GenerateOptions<T, S>): Observable<T>;
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