[racket] [plai] consistent output

I think the plan is to change pconvert so that it prints as `(foo 1
2)' by default (and then change the teaching languages to bring back
the "make" prefixes).

Robby

On Mon, Nov 21, 2011 at 6:50 AM, Jay McCarthy <jay.mccarthy at gmail.com> wrote:
> From your email below, Matthew, I get the impression that you think some of
> this can't be fixed inside the PLAI language itself, because there's no
> other option at the Racket level. Is that correct?
> Jay
>
> On Sun, Nov 20, 2011 at 7:48 AM, Matthew Flatt <mflatt at cs.utah.edu> wrote:
>>
>> 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.
>>
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>
>
> --
> Jay McCarthy <jay at cs.byu.edu>
> Assistant Professor / Brigham Young University
> http://faculty.cs.byu.edu/~jay
>
> "The glory of God is Intelligence" - D&C 93
>
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