The Universe of Discourse

Another Linogram success story
I've been saying for a while that a well-designed system surprises even the designer with its power and expressiveness. Every time linogram surprises me, I feel a flush of satisfaction because this is evidence that I designed it well. I'm beginning to think that linogram may be the best single piece of design I've ever done.

Here was today's surprise. For a long time, my demo diagram has been a rough rendering of one of the figures from Higher-Order Perl:

I wanted component k in the middle of the diagram to be a curved line, but since I didn't have curved lines yet, I used two straight lines instead, as shown below:

        define bentline {
          line upper, lower;
          param number depth = 0.2;
          point start, end, center;
          constraints {
            center = upper.end = lower.start;
            start = upper.start;  end = lower.end;
            start.x = end.x = center.x + depth;
            center.y = (start.y + end.y)/2;
          }
        }

        ...

        bentline k;
        label klbl(text="k") = k.upper.center - (0.1, 0);
        ...
        constraints {
          ...
          k.start = plus.sw; k.end = times.nw;
          ...
        }

I now needed to replace this with a curved line. This meant removing all the references to start, end, upper and so forth, since curves don't have any of those things. A significant rewrite, in other words.

But then I had a happy thought. I added the following definition to the file:

        require "curve";
        define bentline_curved extends bentline {
          curve c(N=3);
          constraints {
            c.control[0] = start;
            c.control[1] = center;
            c.control[2] = end;
          }
          draw { c; }
        }

I then replaced:

        bentline k;

        bentline_curved k;

To make this change, I didn't have to edit or understand the definition of bentline, except to understand a bit about its interface: begin, end, and center. I could build a new definition atop it that allowed the rest of the program to use it in exactly the same way, although it was drawn in a completely different way.

I didn't foresee this when I designed the linogram language. Sometimes when you try a new kind of program for the first time, you keep getting unpleasant surprises. You find things you realize you didn't think through, or that have unexpected consequences, or features that turn out not to be as powerful as you need, or that mesh badly with other features. Then you have to go back and revisit your design, fix problems, try to patch up mismatches, and so forth. In contrast, the appearance of the sort of pleasant surprise like the one in this article is exactly the opposite sort of situation, and makes me really happy.

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