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### 6.11.3 Sorting

Sorting is very important in computer programs. Therefore, Guile comes
with several sorting procedures built-in. As always, procedures with
names ending in `!`

are side-effecting, that means that they may
modify their parameters in order to produce their results.

The first group of procedures can be used to merge two lists (which must be already sorted on their own) and produce sorted lists containing all elements of the input lists.

- Scheme Procedure:
**merge***alist blist less* - C Function:
**scm_merge***(alist, blist, less)* Merge two already sorted lists into one. Given two lists

`alist`and`blist`, such that`(sorted? alist less?)`

and`(sorted? blist less?)`

, return a new list in which the elements of`alist`and`blist`have been stably interleaved so that`(sorted? (merge alist blist less?) less?)`

. Note: this does _not_ accept vectors.

- Scheme Procedure:
**merge!***alist blist less* - C Function:
**scm_merge_x***(alist, blist, less)* Takes two lists

`alist`and`blist`such that`(sorted? alist less?)`

and`(sorted? blist less?)`

and returns a new list in which the elements of`alist`and`blist`have been stably interleaved so that`(sorted? (merge alist blist less?) less?)`

. This is the destructive variant of`merge`

Note: this does _not_ accept vectors.

The following procedures can operate on sequences which are either
vectors or list. According to the given arguments, they return sorted
vectors or lists, respectively. The first of the following procedures
determines whether a sequence is already sorted, the other sort a given
sequence. The variants with names starting with `stable-`

are
special in that they maintain a special property of the input sequences:
If two or more elements are the same according to the comparison
predicate, they are left in the same order as they appeared in the
input.

- Scheme Procedure:
**sorted?***items less* - C Function:
**scm_sorted_p***(items, less)* Return

`#t`

if`items`is a list or vector such that, for each element`x`and the next element`y`of`items`,`(`

returns`less``y``x`)`#f`

. Otherwise return`#f`

.

- Scheme Procedure:
**sort***items less* - C Function:
**scm_sort***(items, less)* Sort the sequence

`items`, which may be a list or a vector.`less`is used for comparing the sequence elements. This is not a stable sort.

- Scheme Procedure:
**sort!***items less* - C Function:
**scm_sort_x***(items, less)* Sort the sequence

`items`, which may be a list or a vector.`less`is used for comparing the sequence elements. The sorting is destructive, that means that the input sequence is modified to produce the sorted result. This is not a stable sort.

- Scheme Procedure:
**stable-sort***items less* - C Function:
**scm_stable_sort***(items, less)* Sort the sequence

`items`, which may be a list or a vector.`less`is used for comparing the sequence elements. This is a stable sort.

- Scheme Procedure:
**stable-sort!***items less* - C Function:
**scm_stable_sort_x***(items, less)* Sort the sequence

`items`, which may be a list or a vector.`less`is used for comparing the sequence elements. The sorting is destructive, that means that the input sequence is modified to produce the sorted result. This is a stable sort.

The procedures in the last group only accept lists or vectors as input, as their names indicate.

- Scheme Procedure:
**sort-list***items less* - C Function:
**scm_sort_list***(items, less)* Sort the list

`items`, using`less`for comparing the list elements. This is a stable sort.

- Scheme Procedure:
**sort-list!***items less* - C Function:
**scm_sort_list_x***(items, less)* Sort the list

`items`, using`less`for comparing the list elements. The sorting is destructive, that means that the input list is modified to produce the sorted result. This is a stable sort.

- Scheme Procedure:
**restricted-vector-sort!***vec less startpos endpos* - C Function:
**scm_restricted_vector_sort_x***(vec, less, startpos, endpos)* Sort the vector

`vec`, using`less`for comparing the vector elements.`startpos`(inclusively) and`endpos`(exclusively) delimit the range of the vector which gets sorted. The return value is not specified.

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