Do Scheme operators have associativity?
Scheme computes (- a b c) as a - b - c, i.e., strictly left to right.

It really makes no sense to talk about associativity in Scheme, which applies to how an otherwise ambiguous expression like a # b # c is to be interpreted, either as (a # b) # c or a # (b # c) (or even forbid such combinations). In Scheme no such ambiguity is possible, everything is prefix. And the function called is responsible to decide what to do with it's arguments, even if the number of arguments is variable (as in this case). It is probably more natural to work left-to-right.