I believe that the current "official" ruling depends on two points:
1) Readied actions take place before the action that triggers them. This is paradoxical, but in essence the original acting character never performs the action.
2) You don't declare actions in advance; if you can interpret what your character has done thus far in multiple ways, you may choose any valid interpretation.
#1 is proven in the SRD by the following sentence under Ready:
It is arguable whether or not "the action that triggers it" must then be performed. I am not sure if the Sage or anyone else has ruled explicitly on this. By the book, then, this could go either way and is up to the DM.
#2 is alluded to (and perhaps stated explicitly; no rulebooks here) in the PHB by a passage which talks about making full attacks: you don't have to choose your targets in advance; instead you can decide what to do after making the first attack. I believe that it also says you can convert a single attack to a full attack (or not) after making the first attack.
I don't believe the book is crystal clear on this, but (lacking a quotation) my recollection is that they intend characters to be able to change their minds mid-action.
With these being stated, here's how I would run it.
1) Attacker closes, suffers AoO
2) Defender's ready action triggers before attacker can attack.
3) Attacker, mid-action, elects to continue their movement action before attacking.
I like this interpretation because it gives players more options, and makes it a little harder to abuse the Ready rules -- not to imply that this example is an abuse.
1) Readied actions take place before the action that triggers them. This is paradoxical, but in essence the original acting character never performs the action.
2) You don't declare actions in advance; if you can interpret what your character has done thus far in multiple ways, you may choose any valid interpretation.
#1 is proven in the SRD by the following sentence under Ready:
The partial action comes before the action that triggers it.
It is arguable whether or not "the action that triggers it" must then be performed. I am not sure if the Sage or anyone else has ruled explicitly on this. By the book, then, this could go either way and is up to the DM.
#2 is alluded to (and perhaps stated explicitly; no rulebooks here) in the PHB by a passage which talks about making full attacks: you don't have to choose your targets in advance; instead you can decide what to do after making the first attack. I believe that it also says you can convert a single attack to a full attack (or not) after making the first attack.
I don't believe the book is crystal clear on this, but (lacking a quotation) my recollection is that they intend characters to be able to change their minds mid-action.
With these being stated, here's how I would run it.
1) Attacker closes, suffers AoO
2) Defender's ready action triggers before attacker can attack.
3) Attacker, mid-action, elects to continue their movement action before attacking.
I like this interpretation because it gives players more options, and makes it a little harder to abuse the Ready rules -- not to imply that this example is an abuse.