One expresses surprise being doubled up in laughter (2-2)
I believe the answer is:
ha-ha
'laughter' is the definition.
(I know that ha-ha is a type of laughter)
'one expresses surprise being doubled up' is the wordplay.
I cannot really see how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is found in the answer.
'surprise' could be 'ha' (I've seen this in other clues) and 'ha' is present in the answer.
A single letter 'h' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for ha-ha that I've seen before include "Loud laugh" , "Funny type of ditch?" , "Ditch used by landscapers" , "Laugh - ditch acting as fence" , "Ditch with a wall in it - that's a laugh" .)