Ah. Often I only realise what's really going on in my life by acting on the assumption that it's actually something different. Don't try this at home, kids, as it may end up with you living in the wrong country, with the wrong number of internal organs, married to a person of the wrong sex. THEN you'll know. Lucky for me, the present instance was not so earth-shattering. But I found out it wasn't to do with passing functions into hashes. They calculate fine in hashes, and my preferred method set out above DOES actually work. So - sorry to waste your time; but thanks for providing a sounding board which obliged me to formulate my problem, and then challenged me to determine whether it was a problem or not. One day I'll be able to do this for myself...

§ George Sherston