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xpl

xpl

 

  1  definition  found 
 
  From  The  Free  On-line  Dictionary  of  Computing  (13  Mar  01)  [foldoc]: 
 
  XPL 
 
  A  small  dialect  of  {PL/I}  used  for  compiler  writing  from 
  Stanford,  1967-69.  XPL  has 
  one-dimensional  {array}s.  I/O  is  achieved  with  character 
  pseudo-variable  INPUT  and  OUTPUT,  e.g. 
 
  OUTPUT  =  'This  is  a  line'; 
 
  It  has  inline  {machine  code}.  "Programmers  are  given  all  the 
  rope  they  ask  for  Novices  tend  to  hang  themselves  fairly 
  frequently."  XPL  has  been  implemented  on  {IBM  360},  {Univac 
  1100},  {ICL  System  4},  {CDC6000}  and  {Cyber}  series,  {XDS 
  Sigma-5}  and  {Sigma-7}  and  {DEC}  {PDP-10}. 
 
  An  optimising  XPL  compiler  (version  1)  by  Robin  Vowels 
    is  a  standard  implementation  of  XPL 
  and  is  based  on  McKeeman  Horning,  and  Wortman's  improved 
  {XCOM}  (which  employs  hashed  symbol  table  generation).  It 
  includes  the  extra  built-in  function  COREHALFWORD 
 
  The  following  areas  have  been  optimised:  procedures  calls  when 
  the  argument  and  corresponding  parameter  are  of  the  same  type 
  and  when  the  argument  is  a  constant;  constant  subscripts;  use 
  of  CORELHALFWORD  and  COREWORD;  string  constants  of  length  one 
  iterative  DO  statements  by  transferring  code  to  the  end  of  the 
  loop. 
 
  String  constants  of  length  one  do  not  require  a  descriptor, 
  hence  more  descriptors  are  available  for  string  variables. 
  Comparison  operations  are  treated  as  commutative,  and  an 
  improved  Commute  algorithm  is  used  Halfword  instructions  are 
  generated  for  BIT(16)  variables. 
 
  These  areas  have  been  improved  or  re-written:  calls  on  OUTPUT, 
  catenation,  integer-to-string  conversion,  multiply,  divide, 
  and  MOD.  An  emitter  for  SS-type  instructions  has  been  added. 
  The  compiler  achieves  an  11%  reduction  in  object  code 
  compiling  itself  an  11%  increase  in  compilation  rate,  a  55% 
  increase  in  compilation  speed  when  the  $E  toggle  is  set 
  Special  treatment  for  catenating  a  string  to  an  integer 
  substantially  decreases  consumption  of  the  free  string  area, 
  and  decreases  string  moves  The  latter  improvement  is  most 
  noticeable  on  small  core  machines. 
 
  Core  requirements:  less  than  the  improved  XCOM  on  which  it  is 
  based  (approx.  98000  bytes).  Symbol  table  size  is  468. 
  Ported  to  {IBM}  {System  370}.  The  compiler  is  written  in  XPL. 
  The  code  generators  are  machine-specific. 
 
  ["A  Compiler  Generator,"  W.M.  McKeeman  et  al  P-H  1970]. 
 
  [JCC,  AFIPS  1968]. 
 
  (1993-08-07)