Users and groups
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User ids & group ids are boxed integers that represent Unix users & groups.  Also, every user & group has a corresponding user info or group info record, which contains miscellaneous information about the user or group.  The procedures in this section are exported by the structures posix-users & posix.

 -- procedure: user-id? object returns boolean
 -- procedure: user-id=? uida uidb returns boolean
 -- procedure: user-id->integer uid returns integer
 -- procedure: integer->user-id integer returns uid
 -- procedure: group-id? object returns boolean
 -- procedure: group-id=? gida gidb returns boolean
 -- procedure: group-id->integer gid returns integer
 -- procedure: integer->group-id integer returns gid
     User-id? & group-id? are the disjoint type predicates for user & group ids.  User-id=? & group-id=? test whether two user or group ids, respectively, are the same, ie whether their numbers are equal.  User-id->integer, group-id->integer, integer->user-id, & integer->group-id convert between user or group ids and integers.

 -- procedure: user-id->user-info uid returns user-info
 -- procedure: name->user-info string returns user-info
 -- procedure: group-id->group-info gid returns group-info
 -- procedure: name->group-info string returns group-info
     These provide access for the user or group info records that correspond with the given user or group ids or names.

 -- procedure: user-info? object returns boolean
 -- procedure: user-info-name user-info returns string
 -- procedure: user-info-id user-info returns user-id
 -- procedure: user-info-group user-info returns group-id
 -- procedure: user-info-home-directory user-info returns string
 -- procedure: user-info-shell user-info returns string
 -- procedure: group-info? object returns boolean
 -- procedure: group-info-name group-info returns string
 -- procedure: group-info-id group-info returns group-id
 -- procedure: group-info-members group-info returns user-id-list
     User-info? & group-info? are the disjoint type predicates for user info & group info records.  The others are accessors for the various data available in those records.