R7RS-small has the right kind of define-record-type

vector->list of the kind you want is in R7RS-small

Suggested name changes, mostly to align with SRFI 1:

transduce -> list-transduce

Semantics:

tdedupe and tremove-duplicates need to accept an equality predicate.  If the underlying hash table package can't handle arbitrary equality predicates, it should at least handle eq?, eqv?, and equal?.

tremove-duplicates needs to specify which element is retained, presumably the earliest.

I don't understand the purpose of the tref argument to thalt-when.  Without

this argument it seems to be the same as drop-while, except with the

predicate negated.  Add some more explanation clarifying its purpose.

Implementation issues:

Don't encourage the use of reverse!.  It can be very slow when the garbage collector has a write barrier, because it mutates every pair, in which case it is faster to use a functional reverse.

Markup:

ttake and tdrop (in the transduce procedure) need to be in code font.

Same with treplace in the treplace procedure.

In thalt-when, pred? is code font instead of italics.

John Cowan          http://vrici.lojban.org/~cowan        xxxxxx@ccil.org
Knowledge studies others / Wisdom is self-known;
Muscle masters brothers / Self-mastery is bone;
Content need never borrow / Ambition wanders blind;
Vitality cleaves to the marrow / Leaving death behind.    --Tao 33 (Bynner)