status: final (2014-11-28)
keywords: Data Structure, R7RS Large, R7RS Large: Red Edition
Scheme currently does not provide immutable
pairs corresponding to its existing mutable pairs, although most uses of
pairs do not exploit their mutability. The Racket system takes the radical approach
of making Scheme's pairs immutable, and providing a minimal library of
mutable pairs with procedures named mpair?, mcons, mcar, mcdr,
set-mcar!, set-mcdr!. This SRFI takes the opposite approach of
leaving Scheme's pairs unchanged and providing a full set of routines for
creating and dealing with immutable pairs. The sample implementation is
portable (to systems with SRFI 9) and efficient.