I've been programming in lisp pretty much daily since the 1970s. I've also programmed in probably 50 other languages under as many different development methodo

I've been programming in lisp pretty much daily since the 1970s. I've also programmed in probably 50 other languages under as many different development methodologies. The methodology described in the posting does exist, but it is never used for development; it is, however, very commonly used in three settings: (1) one-shot short programming [1SP], (2) exploratory programming [XP], and (3) interactive debugging [ID]. I just last night did an examples of 1SP: I was trying to work out the equation for a combinatorial probability, and wanted to simulate it so that I could tell what the right answer should be. I wrote the simulation expression right into the REPL -- not even in EMACS (my usual mode of programming is emacs+shell(usually lisp) -- I'm so old-timey that I never even bothered to install SLIME!) It took a couple copy-paste fixes to get it to work, but in a couple minutes, I had my result. I do XP all the time, but usually on a single function, or small set of them, often when I'm trying to make a complex recursion work. This is like 1SP, but I'm not going to throw away the code; to the contrary, I'm going to copy the final, hopefully working, code into the body of my program. Therefore, I'll often do XP in an emacs+shell(lisp). ID needs no further explanation; this is well described in the posting, and is, as mentioned, quite a wonderful process. (Sometimes ID and XP are mixed, as suggested in the posting.) What never even happens is complete software development in lisp "core" -- what's sometimes called "workspace" development. This can be done, but it's a terrible software engineering methodology. (APL, which I've also done quite a lot of, although not so much anymore, has had a REPL since around the same time as Lisp, and has always worked in the workspace parading, and it was always a terrible mess for anything very complex.) [BASIC also had a workspace paradigm and REPL since around the same time as Lisp, but no one did anything big in the early BASICs, so this was fine. They were mostly used by student on early timesharing systems.] One very important and under-appreciated property of Lisp that really makes interactive programming work so well in Lisp, and not so well in most other languages, is that line turns and white space make no difference at all to Lisp; it's all from the first open paren to the last close, so you can copy-paste whole expressions into the place of variables, if you like (more commonly the other way around, I guess), and there's never any question about it being syntactically correct. For example, I take this expression: (foo (bar (baz ...)) (bar (baz ...))) where, say, (bar (baz ...)) is a heavy computation, so I want to refactor it. All I need to do is pull the expression (bar (baz ...)) out using paren-matching, wrap the thing in a let, and bob's your uncle, as: (let ((x (bar (baz ...)))) (foo x x)) But the thing to note it that the expression (bar (baz ...)) could be 50 lines long! As I said above, line turns and white space (aside from enough white space to break up obvious things, like the names of separate variables), are mere decoration to Lisp, so you can decorate, or not, all you want. This facility to not care at all about the lines and spacing, which most other languages care about in one or another way; make interactive programming a real joy.