Sorting

This chapter describes the `(rnrs sorting (6))`library for
sorting lists and vectors.

*Proc* should accept any two elements
of *list* or *vector*, and should not have any side
effects. *Proc* should return a true value when its first argument
is strictly less than its second, and `#f` otherwise.

The `list-sort` and `vector-sort` procedures perform a stable
sort of *list* or *vector* in ascending order according to
*proc*, without changing *list* or
*vector* in any way. The `list-sort` procedure returns a
list, and `vector-sort` returns a vector. The results may be `eq?` to the argument when the argument is already sorted, and the
result of `list-sort` may share structure with a tail of the
original list. The sorting algorithm performs *O*(*n* lg *n*) calls to
*proc* where *n* is the length of *list* or *vector*,
and all arguments passed to *proc* are elements of the list or
vector being sorted, but the pairing of arguments and the sequencing
of calls to *proc* are not specified.
If multiple returns occur from `list-sort` or `vector-sort`, the return
values returned by earlier returns are not mutated.

(vector-sort < '`#`(3 5 2 1)) ⇒ `#`(1 2 3 5)

*Implementation responsibilities: *The implementation must check the restrictions
on *proc* to the extent performed by applying it as described.
An
implementation may check whether *proc* is an appropriate argument
before applying it.

*Proc* should accept any two elements
of the vector, and should not have any side
effects. *Proc* should return a true value when its first
argument is strictly less than its second, and `#f` otherwise.
The `vector-sort!` procedure destructively sorts *vector* in
ascending order according to *proc*. The sorting algorithm
performs *O*(*n*^{2}) calls to *proc* where *n* is the length of
*vector*, and all arguments passed to *proc* are elements
of the vector being sorted, but the pairing of arguments and the
sequencing of calls to *proc* are not specified. The sorting
algorithm may be unstable. The procedure returns unspecified values.

(vector-sort! < v) ⇒ *unspecified*

v ⇒ `#`(1 2 3 5)

`
`*Implementation responsibilities: *The implementation must check the restrictions
on *proc* to the extent performed by applying it as described.
An
implementation may check whether *proc* is an appropriate argument
before applying it.