Algol 60

ALGOL 60 is short for *Algorithmic Language 1960. It was the first language to implement nested function definitions with lexical scope. It inspired many other languages including Pascal, Scheme, and C. While it’s mostly obsolete these days, it is a language that was highly influential on both the practice and theory of computer programming since its invention in the 1950s.

Example of a simple program, printing “Hello world!” five times:

'BEGIN'
'COMMENT' Hello World program for ALGOL 60;
    'INTEGER' I;

    'FOR' I := 1 'STEP' 1 'UNTIL' 5 'DO'
    'BEGIN'
         OUTSTRING(1, '('Hello world!')');
         SYSACT(1, 14, 1);
    'END'
'END'

Code blocks start with begin and close with end. Indentation is not important except for readability.

The algol60 report was the first publication using BNF notation to describe the grammar for a language.