XPL
A small dialect of {
PL /
I }
used for compiler writing from
Stanford ,
1967 -
69 .
XPL has
one -
dimensional {
arrays }.
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 }, {
CDC 6000 }
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 )
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