At Sun, 20 Nov 2011 09:31:02 -0300, Eric Tanter wrote: > By default, #lang plai prints out values as follows in the REPL: > > (define-type Foo > (foo (x number?))) > > > (foo 1) > (foo 1) > > (list 1 2) > '(1 2) > > The output is not really consistent, in that foo is printed as a (user-level) > constructor, but list is not.
Well, `quote' is playing the role of constructor. > For teaching, the problem with output '(1 2) is > the need to explain (or try to ignore) the quote. PLAI uses `quote' for lists starting on page 8, so if you're teaching with the book, it may not be worthwhile to avoid `quote'. I think my students has had little trouble with `quote'. In contrast, in the bad old days when the `quote' was missing --- so that `(list 1 2)' printed as just `(1 2)' --- students had a difficult time with the difference between expressions and printed values. > If I change the output configuration to "constructor", then I get: > > > (foo 1) > (make-foo 1) > > (list 1 2) > (list 1 2) > > Now list is printed as constructor, but foo is printed using its "low-level" > constructor, which for teaching is not that great either. Agreed --- this should be fixed. Currently, constructor-style printing always uses a "make-", but the default mode should be to use the same constructor name that `print' uses when `print-as-expression' is true. > The other option for output is "write", which gives: > > > (foo 1) > #(struct:foo 1) > > (list 1 2) > (1 2) > > Again not so nice. Agreed --- definitely not the right option for teaching. > Basically, there seems to be no way to obtain: > > > (foo 1) > (foo 1) > > (list 1 2) > (list 1 2) > > Is there? Right -- not until we fix constructor-style printing. _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
