What is the earliest use of the “this” keyword in any programming language?

I understand the this (or self or Me) is used to refer to the current object, and that it is a feature of object-oriented programming languages. The earliest language I could find which has such a concept was Smalltalk, which uses self but was wondering where and when (which programming language) the concept was first implemented?

Simula 67 is generally considered the first object-oriented language and predates Smalltalk by a number of years.

It also used the this keyword for the same concept, which can be seen in this book chapter extract:

  class Linker;
begin
text ID;

begin

procedure Onto_Lists(Gender,Occupation);
name Gender,Occupation;
begin
Sex :- Gender;
Employment :- Occupation;
Gender :- Occupation :- this Linker
end..of..Onto..Lists;

InImage;
ID :- Copy(SysIn.Image);
InImage;

• Interesting! What's up with those end.. and end-- bits? Do they constitute part of the syntax? – jogloran Mar 7 at 21:31
• @jogloran: The Vim syntax-highlighting rules for Simula says: "Text between the keyword 'end' and either a semicolon or one of the keywords 'end', 'else', 'when' or 'otherwise' is also a comment." [link] That's obviously not authoritative -- it just means that Vim would color the ..of..Onto..Lists and --of--Linker and so on as comments -- but judging from the examples in the book chapter and elsewhere, I think that they are indeed optional comments (albeit not wholly freeform). – ruakh Mar 7 at 22:22
• FWIW, a book I have here called "Introduction to Simula 67" gives the same rule as the Vim rule set mentioned by @ruakh, i.e. comments can directly follow the keyword END but may not contain any of the following: ;, END, WHEN, OTHERWISE, ELSE. Comments in the block body need to start with the keyword COMMENT. – njuffa Mar 8 at 0:04