Caller out to engage occasionally good Swiss singer? (8)
I believe the answer is:
yodeller
'swiss singer?' is the definition.
'yodeller' can be an answer for 'singer?' (yodeller is a kind of singer). I am unsure of the 'swiss' bit.
'caller out to engage occasionally good' is the wordplay.
'caller out' becomes 'yeller' (I can't explain this - if you can you should give a lot more credence to this answer).
'to engage' means one lot of letters goes inside another (some letters get engaged in others).
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
The alternate letters of 'good' are 'od'.
'yeller' going around 'od' is 'YODELLER'.
Can you help me to learn more?
(Other definitions for yodeller that I've seen before include "Alpine singer" , "Vocalist" , "Singer using falsetto" , "Mountain air for him" .)