PLUS - Introduction
The PLUS language holds a special place in the history of MTS - let’s look at it in more detail.
PLUS
PLUS was created by Alan Ballard and Paul Whaley of the University of British Columbia in the 1970s, based on language work done for a previous experimental OS called SUE. According to the HELP pages for PLUS:
PLUS is superficially quite different from Sue or Pascal; however the underlying language semantics are really very similar. Users familiar with the programming language C will also recognize much of its structure and semantics in PLUS.
PLUS on MTS
PLUS was used heavily at MTS sites as a system development language, as it provides a structured programming environment easier to use than lower level languages, while still allowing access to machine level features in a way a more generic language such as Pascal did not. The implementation also came with a large source library that made writing complex programs easier. It could generate object code both for the System/360 and both PDP/11 and Motorola 68000 systems.
The compiler was written in PLUS and the source can be found on the distribution tapes under component 1042.
Prerequisites
No special installation instructions to get this language running - just do the standard D6.0 setup as described in this guide and then sign on as a regular user such as ST01.
Compiling and running a program
The *PLUS compiler takes its input from scards and writes output to spunch, like many other language translators.
$run *PLUS scards=hello.plus spunch=-load
Hello world
Let’s show this in action. Assume we have a program in the file hello.plus, let’s look how we’d list, compile and run it.
# $list hello.plus
1 %Title := "Hello World Program";
2
3 %Include(Sprint_String, Main);
4
5 definition Main;
6 variable Count is Integer;
7 do Count := 1 to 5
8 Sprint_String("Hello, world!");
9 end do;
10 end Main;
# $run *plus scards=hello.plus spunch=-load
# Execution begins 07:26:15
Hello World Program User REL. Fri May 3/19 07:26:16 Page 1
1. 1 |%Include(Sprint_String, Main); hello.plus
No messages for global String_Types.
Global size 0 bytes.
No messages for global Numeric_Types.
Global size 0 bytes.
****************************************************************************************
* *
* procedure Main *
* parameter is Par (ref). *
* result is Rc. *
* external name is "MAIN ". *
* *
****************************************************************************************
24810. 1 |definition Main;
6. 2 | variable Count is Integer;
7. 3 | do Count := 1 to 5
8. 1 | Sprint_String("Hello, world!");
9. 25 | end do;
10. 26 |end Main;
No messages for procedure Main.
215 bytes code generated; 424 bytes stack required.
String_Types Numeric_Types Main Mts_Io_Types Main Page 1
Plus/370 Compilation -- University of Michigan -- Version 28/16 User REL. Fri May 3/19 07:26:16 Page 2
C r o s s R e f e r e n c e
+------------------------------------------------+ Sprint_String macro 1:8 1:4
| References are of form page:coordinate,... | Sprint_Varying macro 1:7 1:7
| | Standard_String_Length
| Codes used are: | constant 1:2 1:3,4,5
| D - procedure definition | Str macro parm 1:8 1:23,24
| S - store reference | Str macro parm 1:9 1:6
| @ - pointer dereferenced | String_Length_Type type 1:3 1:8
| A - address taken | String_Types global 1:1
| E - equated or opened | Transmitted_Length field 1:8
| | Varying_String type 1:5 1:5
| * indicates procedures and globals with errors| Varying_String_Length field 1:8
+------------------------------------------------+ Varying_String_Structure_Type
type 1:6
+-------------------------------------------------------------+ Varying_String_Text field 1:9
| Symbol Usage Decl References |
+-------------------------------------------------------------+
Actual_Length field 1:8
Buff parameter 1:15
Count variable 1:2 1:3S
Fdub field 1:17
Fixed_String type 1:4 1:9
Integer type 1:6 1:15,2,19
Len parameter 1:16
Len variable 1:22 1:23S,24A
Line variable 1:5 1:6S,23,24A
Lio_Number field 1:19
Liounit field 1:15
Lnum parameter 1:18
Main procedure 1:17 1:1D
Main_Procedure_Type type 1:12 1:17
Maximum_Integer constant 1:4 1:5,6
Maximum_Length field 1:8
Maximum_Short_Integer constant 1:2 1:3,7
Minimum_Integer constant 1:5 1:6
Minimum_Short_Integer constant 1:3 1:7
Mods parameter 1:17
Mts_Fdub_Kind constant 1:10 1:16
Mts_Fdub_Type type 1:2 1:17
Mts_Io_Extended_Modifiers_Type
type 1:5
Mts_Io_Length_Type type 1:6
Mts_Io_Modifiers_Type type 1:4
Mts_Io_Types global 1:1
Mts_Io_Unit_Type type 1:11
Mts_Line_Number_Type type 1:3 1:18
Mts_Lio_Number_Kind constant 1:10 1:18
Mts_Liounit_Kind constant 1:10 1:14
Mts_Unit_Kind_Type type 1:10 1:13
Notification result 1:19
Numeric_Types global 1:1
Par parameter 1:14
Rc result 1:15
Short_Integer type 1:7 1:8,16,22
Sprint procedure 1:21 1:24
Sprint_Procedure_Type type 1:13 1:21
Page 2
Plus/370 Compilation -- University of Michigan -- Version 28/16 User REL. Fri May 3/19 07:26:16 Page 3
The following libraries were specified for this compilation:
*PLUS.SOURCELIB 9 members included.
Total code generated: 215 (bytes)
Total warning messages: 0
Total error messages: 0
# Execution terminated 07:26:15 T=0.075
# $run -load
# Execution begins 07:26:23
Hello, world!
Hello, world!
Hello, world!
Hello, world!
Hello, world!
# Execution terminated 07:26:23 T=0.001
In the next article, we’ll look at the features of PLUS in more detail.
Further information
A paper describing Project SUE can be found at the ACM website.
The main language tutorial and reference is at Bitsavers along with the source library reference.