own family for glm()

Is it possible in R to create a customized family to be used with glm()? I
see no mention of this possibility in the documentation. (S-plus has
something called make.family).

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I.White
ICAPB, University of Edinburgh
Ashworth Laboratories, West Mains Road
Edinburgh EH9 3JT
Fax: 0131 650 6564  Tel: 0131 650 5490
E-mail: iwhite at staffmail.ed.ac.uk