= readdir: read directory and sort files     include "readdir.m";    readdir := load Readdir Readdir->PATH;     NAME, ATIME, MTIME, SIZE, NONE: con iota;    COMPACT:    con (1<<4);    DESCENDING: con (1<<5);    init:    fn(path: string, sortkey: int): (array of ref Sys->Dir, int);    readall: fn(fd: ref Sys->FD, sortkey: int): (array of ref Sys->Dir, int);    sortdir: fn(a: array of ref Sys->Dir, key: int): (array of ref Sys->Dir, int); Readdir provides functions to read and sort the contents of adirectory.  Each function returns its result as a tuple  thatrepresents  the  directory contents as an array of referencesto Sys->Dir values, one  per  file  (see  sys-stat(2)  for  adescription of Dir).  The integer element of the tuple is thenumber of entries returned, or -1 if there was an error read‐ing  the  directory.  Readdir differs from sys-dirread (2) inreturning the contents of the whole  directory,  not  just  achunk of it, and in allowing the result to be sorted. Init  is most often used: it reads the contents of the direc‐tory path and sorts the resulting array according to sortkey. The sorting criteria for the  returned  array  are  based  onsortkey as follows: NAME   Sort files alphabetically by name. ATIME  Sort  files  by  access  time,  most recently accessed       first. MTIME  Sort files by modification time, most  recently  modi‐       fied first. SIZE   Sort files by size, largest file first. NONE   Files are left in directory order, unsorted. If the value DESCENDING is or'd into any of the values above,except NONE, the order of sorting is reversed. The sort used is stable,  of  particular  importance  in  thepresence  of  duplicate names in a union mount.  If the valueCOMPACT is or'd into any of the values above, including NONE,only  the  first  (outermost) entry with a given name will bereturned from reading a union mount, if names are  duplicatedin the union. Readall  reads  file  descriptor  fd  which must be open on adirectory, and returns the contents after applying sortkey asdescribed above for init. Sortdir  sorts  the  array  a  according to the given key, asdefined earlier,  except  that  the  COMPACT  option  has  noeffect. == source/appl/lib/readdir.b == see ALSOsys-dirread(2)