## Module (chicken sort)

This module contains several procedures which deal with sorting of *sequences* (i.e., lists and vectors).

### merge

*[procedure]*

`(merge LIST1 LIST2 LESS?)`

*[procedure]*

`(merge! LIST1 LIST2 LESS?)`

Joins two lists in sorted order. `merge!` is the destructive version of merge. `LESS? ` should be a procedure of two arguments, that returns true if the first argument is to be ordered before the second argument.

### sort

*[procedure]*

`(sort SEQUENCE LESS?)`

*[procedure]*

`(sort! SEQUENCE LESS?)`

Sort `SEQUENCE`, which should be a list or a vector. `sort!` is the destructive version of sort.

### sorted?

*[procedure]*

`(sorted? SEQUENCE LESS?)`

Returns true if the list or vector `SEQUENCE` is already sorted.

### topological-sort

*[procedure]*

`(topological-sort DAG PRED)`

Sorts the directed acyclic graph dag `DAG` so that for every edge from vertex u to v, u will come before v in the resulting list of vertices.

`DAG` is a list of sublists. The car of each sublist is a vertex. The cdr is the adjacency list of that vertex, i.e. a list of all vertices to which there exists an edge from the car vertex. `pred` is procedure of two arguments that should compare vertices for equality.

Time complexity: O (|V| + |E|)

(topological-sort '((shirt tie belt) (tie jacket) (belt jacket) (watch) (pants shoes belt) (undershorts pants shoes) (socks shoes)) eq?) => (socks undershorts pants shoes watch shirt belt tie jacket)

If a cycle is detected during the sorting process, an exception of the condition kinds `(exn runtime cycle)` is thrown.

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