In 1965, Peter Landin presented the groundbreaking paper "The Next 700 Programming Languages" at the ACM Programming Languages and Pragmatics Conference in San

In 1965, Peter Landin presented the groundbreaking paper "The Next 700 Programming Languages" at the ACM Programming Languages and Pragmatics Conference in San Dimas. It described a family of languages called ISWIM, with a staggering number of durable inventions. It's widely recognized as the precursor to ML and Haskell. One of the inventions is the "off-side rule" for indentation sensitive parsing. The last section of the paper, after the author's conclusion, is a transcript of the discussion at the conference. The first question is from Naur: Regarding indentation, in many ways I am in sympathy with this, but I believe that if it came about that this notation were used for very wide communication and also publication,you would regret it because of the kind of rearrangement of manuscripts done in printing, for example. You very frequently run into the problem that you have a wide written line and then suddenly you go to the Communications of the ACM and radically, perhaps, you have to compress it. The printer will do this in any way he likes; he is used to having great freedom here and he will foul up your notation. Next, Floyd: Another objection that think is quite serious to indentation is that while it works on the micro-scale—that is, one page is all right—when dealing with an extensive program, turning from one page to the next there is no obvious way of indicating how far indentation stretches because there is no printing at all to indicate how far you have indented. I would like you to keep that in mind. It's a very old discussion.