IMO impure functional languages like Common Lisp, ML, Scheme, and the somewhat ironically named Pure language are straightforward extensions of imperative programming: you can make your code less imperative without being completely deprived of it.  All of these are tail-recursive (formally CL is not, but most implementations are) which means that recursive loops become non-recursive gotos, and for/do-loops wind up being pure without you noticing.

John Cowan          http://vrici.lojban.org/~cowan        cowan@ccil.org
If a traveler were informed that such a man [as Lord John Russell] was
leader of the House of Commons, he may well begin to comprehend how the
Egyptians worshiped an insect.  --Benjamin Disraeli