RTL/2

The data types in RTL/2 were strongly typed, with separate compiling. The compilation units contained one or more items named bricks, i.e.:

• Procedure bricks
• Data bricks
• Stack bricks

A procedure brick was a procedure, which may or may not return a (scalar) value, have (scalar) parameters, or have local (scalar) variables. The entry mechanism and implementation of local variables was reentrant. Non-scalar data could only be accessed via reference (so-called REF variables were considered scalar).

A data brick was a named static collection of scalars, arrays and records. There was no heap or garbage collection, so programmers had to implement memory management manually.

A stack brick was an area of storage reserved for running all the procedures of a single process and contained the call stack, local variables and other housekeeping items. The extent to which stack bricks were used varied depending on the host environment in which RTL/2 programs ran.

Access to the host environment of an RTL/2 program was provided via special procedure and data bricks called SVC procedures and SVC data. These were accessible in RTL/2 but implemented in some other language in the host environment.

TITLE Hello World;

LET NL=10;

EXT PROC(REF ARRAY BYTE) TWRT;

ENT PROC RRJOB() INT;

TWRT("Hello World#NL#");

RETURN(1);

ENDPROC;

RTL/2 compiles to assembly language and provides the CODE statement to allow including assembly language in RTL/2 source code. This is only available when compiled with a systems programming option (CN:F)

The CODE statement takes two operands: the number of bytes used by the code insert and the number of bytes of stack used.

Within code statements two trip characters are used to access RTL/2 variables. These vary between different operating systems. On a Digital Equipment Corporation (DEC) PDP-11 running RSX-11M, and a VAX running VMS, the trip characters are * and /.

While the specifics varied by operating system the following is an example of a code insert on VAX/VMS:

CODE 6,0;

JMP CODE_ENT ; This code insert can be set to a fixed length as it jumps to a new psect.

; this method is especially useful on systems such as VMS where the length of

; instructions is variable

.SAVE_PSECT ; Save current program section

.PSECT ASMB_CODE,EXE,NOWRT,LONG

CODE_ENT:

MOVL *PARAM1(AP),*COUNTER/MYDATA

JMP CODE_EX

.RESTORE_PSECT

CODE_EX:

• RTL

This code insert moves the value of a variable passed into the RTL/2 procedure into a variable named COUNTER in a data brick named MYDATA.

{{Columns-list|colwidth=10em|

{{Plainlist|

• ABS
• AND
• ARRAY
• BIN
• BLOCK
• BY
• BYTE
• CODE
• DATA
• DO
• ELSE
• ELSEIF
• END
• ENDBLOCK
• ENDDATA
• ENDPROC
• ENT
• EXT
• FOR
• FRAC
• GOTO
• HEX
• IF
• INT
• LABEL
• LAND
• LENGTH
• LET
• LOR
• MOD
• NEV
• NOT
• OCT
• OF
• OPTION
• OR
• PROC
• REAL
• REF
• REP
• RETURN
• RTL
• SHA
• SHL
• SLA
• SLL
• SRA
• SRL
• STACK
• SVC
• SWITCH
• THEN
• TITLE
• TO
• VAL
• WHILE

}}

}}

{{Reflist}}

SPL published a range of documentation for RTL/2. Each such document was assigned a reference number. The following is an incomplete list.

RTL/2 Ref 1 – RTL/2 Language Specification

RTL/2 Ref 2 – Introduction to RTL/2

RTL/2 Ref 3 – RTL/2 Training Manual

RTL/2 Ref 4 – System Standards

RTL/2 Ref 5 – Stream I/O

RTL/2 Ref 18 – Hints on writing RTL/2 Programs

RTL/2 Ref 26 – Language Reference Card

RTL/2 Ref 39 – Run time environment on the PDP-11

RTL/2 Ref 63 – User Manual for the PDP-11 under RSX-11M

RTL/2 Ref 107 – VAX/VMS RTL/2 User Manual

RTL/2 REF 130 – The RTL/2 32-bit run time environment on the VAX

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Category:ALGOL 68 dialect

Category:Procedural programming languages