Hi Tony,

On Wed, Jan 31, 2018 at 3:37 PM, <commits@source.squeak.org> wrote:
A new version of Kernel was added to project The Inbox:
http://source.squeak.org/inbox/Kernel-tonyg.1148.mcz

==================== Summary ====================

Name: Kernel-tonyg.1148
Author: tonyg
Time: 31 January 2018, 11:37:21.27021 pm
UUID: 2a675301-406b-4222-9599-84358a7cc506
Ancestors: Kernel-eem.1147

Brings the Promise implementation closer to Javascript/A+ promises in two ways:
        * Resolving a Promise with another Promise causes them to be chained together
        * Resolving or Rejecting a Promise that is not pending is a no-op, like the Firefox/Chrome/etc in-browser promise implementations.
The tests have been changed in KernelTests-tonyg.331 accordingly.

=============== Diff against Kernel-eem.1147 ===============

Item was changed:
  Object subclass: #Promise
+       instanceVariableNames: 'value resolvers mutex state error rejecters'
-       instanceVariableNames: 'onError value resolvers mutex state error rejectors rejecters'
        classVariableNames: ''
        poolDictionaries: ''
        category: 'Kernel-Processes'!

+ !Promise commentStamp: 'tonyg 1/31/2018 23:34' prior: 0!
- !Promise commentStamp: 'fbs 5/17/2013 18:23' prior: 0!
  I represent the result of an asynchronous message.  Once the message is processed, I will be resolved to a value.  I am typically instantiated by invocations of #futureSend:at:args: (and not by #futureDo:atArgs:).

  See class-comment of FutureNode.

  I also implement the Promises/A+ Javascript specification. This allows you to chain my instances to perform arbitrarily complex asynchronous tasks with error handling baked in.

+ A Promise may be in one of three possible states: #pending, #fulfilled or #rejected. A Promise may move from #pending -> #fulfilled (by way of the resolveWith: message), or from #pending -> #rejected (by way of rejectWith:). No other state changes may occur.
+
+ Once #fulfilled or #rejected, a Promise's value must not change. In keeping with the major Javascript Promise implementations' interpretations of this, calls to resolveWith: or rejectWith: when a Promise is in #fulfilled or #rejected state are simply ignored - an error is not signalled. (See test cases PromiseTest testFirstResolutionWins, testCannotRejectFulfilledPromise and testCannotResolveaRejectedPromise.)!
- A Promise may be in one of three possible states: #pending, #fulfilled or #rejected. A Promise may move from #pending -> #fulfilled, or from #pending -> #rejected. No other state changes may occur. Once #fulfilled or #rejected, a Promise's value must change.!

Item was changed:
  ----- Method: Promise>>rejectWith: (in category 'resolving') -----
  rejectWith: anObject
        "Reject this promise."
        mutex critical: [
+               (state == #pending) ifTrue: [
+                       error := anObject.
+                       state := #rejected.
+                       rejecters do: [:r | self evaluateRejecter: r]]]!
-               (state == #fulfilled) ifTrue: [self error: 'Promise was already resolved'].
-               (state == #rejected) ifTrue: [self error: 'Promise was already rejected'].
-               error := anObject.
-               state := #rejected.
-               rejecters do: [:r | self evaluateRejecter: r]].!

Item was changed:
  ----- Method: Promise>>resolveWith: (in category 'resolving') -----
  resolveWith: arg
+       "Resolve this promise. If arg is itself a Promise, make this promise depend upon it,
+       as detailed in the Promises/A+ spec:
+               https://promisesaplus.com/#the-promise-resolution-procedure"
+
+       (arg isKindOf: Promise)

I'd /much/ rather see Object>>isPromise and Promise>>isPromise than this.
 
+               ifTrue: [
+                       arg whenResolved: [:v | self resolveWith: v].
+                       arg whenRejected: [:e | self rejectWith: e]]
+               ifFalse: [
+                       mutex critical: [
+                               (state == #pending) ifTrue: [
+                                       value := arg.
+                                       state := #fulfilled.
+                                       resolvers do: [:r | self evaluateResolver: r]]]]!
-       "Resolve this promise"
-       mutex critical: [
-               (state == #fulfilled) ifTrue: [self error: 'Promise was already resolved'].
-               (state == #rejected) ifTrue: [self error: 'Promise was already resolved'].
-               value := arg.
-               state := #fulfilled.
-               resolvers do: [:r |
-                       self evaluateResolver: r]].!

Item was changed:
  ----- Method: Promise>>then: (in category 'monad') -----
  then: resolvedBlock
+       ^ self then: resolvedBlock ifRejected: [:e | "Pass rejection reason along" e].!
-       ^ self then: resolvedBlock ifRejected: [:ignored | "Do nothing"].!


_,,,^..^,,,_
best, Eliot