.if !\n(xx .so tmac.p
.RP
.TL
Berkeley Pascal
PX Implementation Notes
.br
Version 1.1 \- April, 1979
.AU
William N. Joy\*(dg
.AI
Computer Science Division
Department of Electrical Engineering and Computer Science
University of California, Berkeley
Berkeley, California  94720
.AB
.PP
Berkeley Pascal
is designed for interactive instructional use and runs on the
\s-2PDP\s0 11 computer family.
..A version of \fIpx\fR for the \s-2VAX\s0 11/780 is nearly complete.
The interpreter
.I px
executes the Pascal binaries generated by the Pascal translator
.I pi .
.PP
The
.I
PX Implementation Notes
.R
describe the overall organization of
.I px ,
detail the various operations of the interpreter,
with a special section describing the file input/output structure.
Conclusions are given as to the viability of an interpreter
based approach to language implementation for an instructional environment.
.AE
.if n 'ND
.SH
Introduction
.PP
This
.I
PX Implementation Notes
.R
consists of four major parts.
The first part outlines the overall organization of
.I px .
Section 2 describes the operations (instructions) of the interpreter
while section 3 focuses on input/output related activity.
A final section gives conclusions about the viability of an interpreter
based approach to language implementation for instruction.
.SH
Related Berkeley Pascal documents
.PP
The
.I "PXP Implementation Notes"
give details of the internals of the execution profiler
.I pxp;
parts of the interpreter related to
.I pxp
are discussed in section 2.10.
A paper describing the syntactic error recovery mechanism used in
.I pi
will be presented at the ACM Conference on Compiler Construction
in Boulder Colorado in August, 1979.
.SH
Acknowledgements
.PP
This version of
.I px
is heavily based on an earlier
.I px
which was designed and implemented by Ken Thompson,
the author of the first
.UP
system.
Without his work, this
.UP
system would never have existed.
Charles Haley, who collaborated with the author on this project, wrote
some of the more difficult input/output routines in this version of
.I px,
and helped to debug it all.
His assistance in teaching this author about
.UX
and Pascal is gratefully acknowledged and appreciated.
The author would also like to thank his faculty advisor Susan L. Graham
for her encouragement,
her helpful comments and suggestions
relating to
.UP
and her excellent editorial assistance.
.FS
\*(dg The financial support of the National Science Foundation under grants
MCS74-07644-A03 and MCS78-07291
and of an \s-2IBM\s0 Graduate Fellowship are gratefully acknowledged.
.FE
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