message: mol-comp prototype tweak
diff: -type ExecutionContext = { getRuntimeCtx(c: Computation<any>): RuntimeContext, subscribe(o: (p: string, compId: number) => void): void }
  +type ExecutionContext = {
  + run<T>(c: Computation<T>, params?: { updateRateMs: number }): Promise<T>,
  + subscribe(o: (p: string, compId: number) => void): void
  +}
  +
  +namespace ExecutionContext {
  + // export interface Synchronous extends ExecutionContext {
  + // run<T>(c: Computation<T>, params?: { updateRateMs: number }): Promise<T>,
  + // }
  -type RuntimeContext = { yield(name: string): Promise<void> | void, createChildContext(): RuntimeContext }
  + // export interface Observable extends ExecutionContext {
  + // run<T>(c: Computation<T>, params?: { updateRateMs: number }): Promise<T>,
  + // }
  + export const Sync: ExecutionContext = 0 as any;
  +}
  +
  +interface RuntimeContext extends ExecutionContext {
  + yield(name: string): Promise<void> | void
  +}
  +// if no context is specified, use the synchronous one.
  type Computation<T> = { (ctx?: RuntimeContext): Promise<T>, _id: number }
  function create<T>(c: (ctx: RuntimeContext) => Promise<T>): Computation<T> { return 0 as any; }
  +function constant<T>(c: T) { return create(async ctx => c); }
  type MultistepFn<P, T> = (params: P, step: (s: number) => Promise<void> | void, ctx: RuntimeContext) => Promise<T>
  type ComputationProvider<P, T> = (params: P) => Computation<T>
  @@ -40,7 +58,7 @@ function readLines(str: string): Computation<string[]> {
  const prependHiToLines = MultistepComputation('Hi prepend', ['Parse input', 'Prepend Hi'], async (p: string, step, ctx) => {
  await step(0);
  - const lines = await readLines(p)(ctx);
  + const lines = await ctx.run(readLines(p));
  await step(1);
  const ret = lines.map(l => 'Hi ' + l);
  return ret;
  @@ -48,6 +66,6 @@ const prependHiToLines = MultistepComputation('Hi prepend', ['Parse input', 'Pre
  (async function() {
  - const r = await prependHiToLines('1\n2')();
  + const r = await ExecutionContext.Sync.run(prependHiToLines('1\n2'), { updateRateMs: 150 });
  console.log(r)
  }())
  