Building Setf

setf is one of the most underrated Lisp powers. In Javascript, it'd look like this:

  // save current cursor position
  var x = point();

  // set the cursor position
  point() = 42;

  // insert some text
  insert("Hi there")

  // reset cursor position
  point() = x;

Notice you're assigning a value to a function call.

Under the hood, point() = x; gets transformed to set_point(x); or whatever else you tell it to do -- it's programmable, and you have full access to the right hand side arguments.

This might not seem too compelling. The key is that it composes.

I was just getting to the good part, but our puppy is demanding my attention. Duty calls.

Suffice to say, nested calls like

  point(find_buffer("foo.txt")) = 21

can be rewritten to

  prev_buffer = current_buffer();
  set_buffer(find_buffer("foo.txt"));
  set_point(21);
  set_buffer(prev_buffer);

automatically.

An article on how to not break to new lines in the middle of a word, makes it hard to read. You can improve by running

  $('.content').style.hyphens = 'none';

flies away