On Mon, Aug 10, 2009 at 6:02 PM, Matthew Flatt<mfl...@cs.utah.edu> wrote: > At Wed, 5 Aug 2009 15:16:57 -0400, Carl Eastlund wrote: >> Is there any chance we can change the default printer to show the >> syntax->datum of syntax objects? Instead of #<syntax> in error >> messages, it would be much more helpful to see something like #'(foo >> x) or #<syntax:(foo x)>. Even the error printer, which cuts off at a >> certain point with "...", would be preferable to the current total >> opacity. > > Yes, I should have done that a long time ago. > > v4.2.1.6 adds a `print-syntax-width' parameter that defaults to 32, > which means that up to 32 characters are used for printing a syntax > object's datum form within `#<syntax>': > > > #'(+ 1 2) > #<syntax::3 (+ 1 2)> > > > (syntax-e #'(+ 1 2)) > (#<syntax::24 +> #<syntax::26 1> #<syntax::28 2>) > > > #'((lambda (x) (x x)) (lambda (x) (x x))) > #<syntax::34 ((lambda (x) (x x)) (lambda (...> > > I don't know whether 32 is the right default. I think there are > probably times when I want to see a compact printed form for syntax > objects (especially when there are several in a list, or something like > that), and I bet that 32 is usually enough characters to tell me what > syntax object I'm looking at. Then again, +inf.0 seems like a more > natural default. For now, I've gone with the more conservative default > (with respect to previous versions), but after trying it out, let me > know if you think some else would be better.
I like this move, but I'd prefer a different interface if we're going to have customizable printing. I propose a 'current-syntax-printer' parameter. If someone wants essentially the old behavior, they can set it to void; for full printing they could use write or pretty-print; the default could be the error printer (has a built-in width and uses "..."). I can't imagine using print-syntax-width to set a different number; if I ever used it, I'd set it to either 0 or +inf.0. Custom printing provides more interesting flexibility. --Carl _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-dev
