= Diskblocks: Block, Disk, tempfile: temporary storage of variable-sized blocks     include "diskblocks.m";    diskblocks := load Diskblocks Diskblocks->PATH;     Block: adt {       addr: big;   # address on file       n:    int;   # size in bytes    };     Disk: adt {       init:    fn(fd: ref Sys->FD, gran: int, maxblock: int): ref Disk;       new:     fn(d: self ref Disk, n: int): ref Block;       release: fn(d: self ref Disk, b: ref Block);       read:    fn(d: self ref Disk, b: ref Block,                   a: array of byte, n: int): int;       write:   fn(d: self ref Disk, b: ref Block,                   a: array of byte, n: int): ref Block;    };     init:     fn();    tempfile: fn(): ref Sys->FD; Diskblocks manages a set of variable-sized blocks on a tempo‐rary file. Init must be called before any other function in the module. Each block has an address and a size in bytes, represented bya value of type Block. Each file is represented by the type Disk, providing the fol‐lowing operations: init(fd, gran, maxblock)       Initialises  the  file  fd  for use as temporary block       storage and returns a reference to a Disk to  describe       it.  Fd must be open for reading and writing, and must       refer to a file that allows random access.  Blocks are       allocated  in  multiples  of  the granularity gran, in       bytes; the largest possible block is  maxblock  bytes,       which must be a multiple of gran. d.new(n)       Allocate  a  block  of  n bytes on Disk d and return a       reference to it. d.release(b)       Free the Block b, making it  available  for  realloca‐       tion. d.write(b, a, n)       Write  n  bytes  from  array  a  to Block b on Disk d,       returning a reference to the resulting Block.  If b is       nil  or  n exceeds b's current size, write allocates a       new block (releasing  b).   Thus  the  returned  value       might differ from b, and must be used in subsequent IO       requests. d.read(b, a, n)       Read n bytes from Block b on  Disk  d  into  array  a,       returning the number of bytes read.  N must not exceed       b.n. Tempfile returns a file descriptor referring to a  newly-cre‐ated temporary file, suitable for use by Disk.init.  The filewill be removed automatically when  the  file  descriptor  isclosed. == source/appl/lib/diskblocks.b == diagnosticsA  function  that  returns  an integer returns -1 on error; afunction that returns a reference returns nil on error.   Thesystem error string is set in either case.