The Computer Science department of the Vrije Universiteit in Amsterdam is where I learned to program.
In Pascal as was usual in those years. Here my interest in compiler writing started, since there was a lot of interest in that subject there.
Two educators there taught me about programming: Professor R.P. van de Riet, and, the then young and later so famous, Professor Andrew S. Tanenbaum.
The first VU Pascal compiler was Pascal-U, initiated by van de Riet, based of course on Wirth’s portable Pascal-P2 compiler/interpreter.
Once this compiler was operational on a Unix PDP-11/45, a Pascal interpreter system was developed called BASIS, to help a student do practical programing work.
Pascal-U July 1977 can be found in a folder called ‘vrije’ on the tape dump at https://www.tuhs.org/Archive/Applications/Usenix_77/ug091377.tar.gz
Header of the Pascal compiler
(*version: 004 date: 1-5-77*) (*-------------------------------------------------------------- | | | P A S C A L C O M P I L E R | | ----------------------------- | | | | This compiler processes PASCAL-U1, a subset of | | of standard PASCAL and has been written in this subset. | | It is a modified version of the PASCAL-P2 compiler as | | distributed by the ETH at Zuerich. | | | | Authors: | | Urs Amann, Kesav Nori, Christian Jacobi | | | | Authors of modification: | | Rudolf van Bottenburg, Johan Stevenson | | Vakgroep Informatica | | Wiskundig Seminarium | | Vrije Universiteit | | A M S T E R D A M | | | ---------------------------------------------------------------*)
Downloads
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Source of Pascal-U compiler |
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User manual of the Pascal-U compiler |
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Archive of Pascal-U compiler Source and man pages and binaries for Unix System 6 |
Note that the archive contains the source of the compiler, but not of the interpreter.
First part of the Pascal-U manual
PASCAL‐U is the name of the dialect of Pascal implemented on the PDP 11/45 under
the UNIX time‐sharing system. This dialect is based on PASCAL‐P as distributed
by the ETH at Zurich. The implementation of PASCAL‐U has been developed by the
vakgroep informatica of the Vrije Universiteit, Amsterdam, The Netherlands.
2.Some history
‐‐‐‐‐‐‐‐‐‐‐‐‐‐
The first plans to implement Pascal on the PDP 11/45 were developed under the
guidance of prof. R.P.van de Riet. In those days (mid 1975) the operating system
was DOS, a single user system. The greatest problem has been the limited ad‐
dress space of the machine. The Pcompiler produces code for a virtual machine,
called the SC machine. Macro expansion of SC instructions to PDP‐11 code was
not feasible due to the addressing limit of the PDP‐11. Therefore the SC in‐
structions were directly encoded and an interpreter was written to execute them.
The following description concerns work carried out by Rob Thomas, Johan Steven‐
son and later on by Rudolf van Bottenburg. The first bootstrap used a CDC Cyber
73 computer on which Pascal was available.
At the end of 1975 a preliminary version was running under DOS. Many changes
have been made to the PASCAL‐P2 compiler, most of them forced by the different
size for variables of the various standard types and the address alignment.
(The Pcompiler foolishly assumed that integers,reals etc. all occupied the same
number of storage units.) At the same time, however, the UNIX time‐sharing sys‐
tem was installed. That required adjusting the Pascal system. The interpreter
was rewritten in the UNIX assembly language, and the SC assembler in the high
level language C.
To minimize the space requirements, some changes were made to the first UNIX
version:
a.based upon static counting of SC‐instructions in the compiler itself, some in‐
structions of 2 or more bytes with a high frequency got a 1‐byte format. This
is not done very systematically, however. Further measurements are needed.
b.a lot of optimization is done concerning label references: offsets instead of
indices, distinction between forward and backward, long and short offsets.
c.the handling of input and output is improved.
This resulted in a 25% saving in space for code, while at the same time the in‐
terpretation speed improved. The 16000 SC‐instructions for the compiler itself
are coded in less than 26000 bytes, inclusive constants. This system is called
the PASCAL‐U1 system.
One of the projects under development in our department, is the BASIS system. It
is used in teaching basic programming techniques to students of several disci‐
plines. BASIS is a big program written in Pascal, in size comparable with the
Pcompiler. One of the reasons to make Pascal available on the PDP 11/45, has
been this BASIS project.
The plans for the near future are:
a.to adopt the improvements of the P4‐compiler with respect to the P2‐compiler.
b.to allow external procedures.
c.to allow the Pascal user to choose between interpretation and execution of ex‐
panded SC‐instructions. For example, one would like to make the scanner of a
compiler fast by execution of its expanded code and leave the other parts in‐
terpreted, since for most programs 20% of the program is responsible for more
than 80% of its execution time.
d.to make some local improvements touched upon in the assembler description.
e.to tune the instruction set of the abstract machine.
MAN page for the PASCAL-U compiler
PC(I) 03/05/77 PC(I)
NAME
pc ‐ PASCAL‐U compiler
SYNOPSIS
pc [‐lpc12rx] file.p [arg1 ...]
DESCRIPTION
pc is the UNIX pascal compiler. It has an optional flag
argument.
If no flags are given, pc compiles the program on file.p
and leaves the bsc‐code on file.b. Diagnostics are written
to standard output. The effect of the flags is as fol‐
lows:
‐l produces a complete listing of the program with error
indications and explained error messages.
‐p makes a partial listing. Only the erroneous lines are
listed.
‐c suppresses code generation, does a syntax and semantic
check only.
‐1 performs pass1 of the compiler, leaves the intermediate
(sc) code on file.i .Pass2 is suppressed, unless the ‐2
flag is given.
‐2 executes pass2 of the compiler and leaves interpretable
bsc‐code on file.b. If given without the ‐1 flag it
expects its input on file.i rather than file.p.
‐r runs the compiled program by calling the interpreter
with file.b as codefile. Arguments given after file.p
are passed.
‐x invokes sc‐code expansion.(not yet implemented)
After an error is detected during pass1, the code generation
is suppressed.
The main differences from standard PASCAL are:
1. The program has no other file than those in the pro‐
gram heading, which have type text.There may be at most
eight files, including the predeclared files input and
output, which are associated with standard input and
output.
2. Formal parameters must not be functions or procedures.
3. All records are packed. The procedure unpack is not
available.
4. The maximum length of string constants is 80.
5. The ordinal value of a set element must lie between 0
‐ 1 ‐
PC(I) 03/05/77 PC(I)
and 63 inclusive.
6. A goto may not lead out of a procedure or function
body.
7. After reset a call of get is necessary to initialize
the buffer of a non‐standard inputfile.
8. The procedure dispose is not available. Mark and re‐
lease are added to manipulate the heap:
mark(anyptr) puts the top of heap address in anyptr.
release(anyptr) restore the top of heap from
anyptr.
FILES
file.p source file
file.i intermediate sc‐code
file.b bsc‐code, interpretable by pi.
/lib/ppass1 pass1
/lib/ppass2 pass2
/lib/pclist error diagnostics
/usr/bin/pi interpreter
SEE ALSO
pi (I), PASCAL‐U1 documentation, PASCAL user manual.
DIAGNOSTICS
The diagnostics are intended to be self‐explanatory.
"Memory Fault" may be given if space is exhausted.
BUGS
Reals can only be written in E‐format. Runtime checks
are not implemented. Omitting the filename in read or
write may give problems. Empty fields in records and empty
statements can give messages. Writeln and readln require
always a parameterlist .
‐ 2 ‐
MAN page for the PASCAL-U interpreter
PI(I) 12/22/76
NAME
pi ‐ the PASCAL‐U interpreter
SYNOPSIS
pi bscfile userfile1 ....
DESCRIPTION
The binary stack computer code (BSC) is read from bsc‐file. The
userfiles are expected to be the actual file parameters to be
substituted for the formal file names given in the pascal program
heading. Standard output and standard input are substituted for
the formal names output and input. The order of the arguments is
assumed to correspond with the order of the remaining formal file
names.
SEE ALSO
pc(I), PASCAL‐U1 documentation, Pascal user manual
DIAGNOSTICS
All error messages are self explanatory. A memory fault
can also indicate: no room left