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24.3 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.

 merge alist blist less Scheme Procedure scm_merge (alist, blist, less) C Function
 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.

 merge! alist blist less Scheme Procedure scm_merge_x (alist, blist, less) C Function
 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.

 sorted? items less Scheme Procedure scm_sorted_p (items, less) C Function
 Return #t iff items is a list or a vector such that for all 1 <= i <= m, the predicate less returns true when applied to all elements i - 1 and i

 sort items less Scheme Procedure scm_sort (items, less) C Function
 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.

 sort! items less Scheme Procedure scm_sort_x (items, less) C Function
 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.

 stable-sort items less Scheme Procedure scm_stable_sort (items, less) C Function
 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.

 stable-sort! items less Scheme Procedure scm_stable_sort_x (items, less) C Function
 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.

 sort-list items less Scheme Procedure scm_sort_list (items, less) C Function
 Sort the list items, using less for comparing the list elements. This is a stable sort.

 sort-list! items less Scheme Procedure scm_sort_list_x (items, less) C Function
 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.

 restricted-vector-sort! vec less startpos endpos Scheme Procedure scm_restricted_vector_sort_x (vec, less, startpos, endpos) C Function
 Sort the vector vec, using less for comparing the vector elements. startpos and endpos delimit the range of the vector which gets sorted. The return value is not specified.