[Jscheme-user] Re: trimming listener output

[Timothy J H. <tjh...@br...>]

Hi Robert,

On Mar 10, 2005, at 12:58 PM, Robert MacIntyre wrote:
---snip---
> I'm after a slightly different target.  I have lots of ways to adjust
> the output of a program I write, but I want to fix the top-level
> interactive interpreter itself.  Coming from a background of using
> Allegro CL, I want the scheme interpreter to be more convenient for
> interactive development.  In Allegro, if I type something that returns
> a 10000-element list, it (by default) prints the first 10 elements
> plus ellipsis, rather than crashing emacs.  And if an error occurs, I
> get a short message and some options, rather than a stack dump.  I
> realize jscheme can't do all this right away, but it can do better.
>
> The tricky part is fixing it without breaking other things, since it
> looks like the read-eval-print loop is used for lots of things other
> than direct user interaction.
True ...
>  I can think of a few approaches: (1)
> break the non-interactive case (bad, but all I have so far), (2) write
> my own REPL in scheme and invoke it at startup, (3) write a similar
> function in java, or (4) add conditionals to the main one to somehow
> distiguish between interactive and non-interactive use.  I prefer #4
> for the sake of other future jscheme users, but it's probably the
> hardest to get right.  Perhaps it would be safer to start with some
> variation of #3?

I think 4 is a reasonable approach.
The easiest thing to do as a first step is to create a public static int
variable to that gives the global print depth (zero for infinite depth?
zero by default?) The REPL could set it to a reasonable value for
interactive sessions. We could specify an interactive session on
the command line:

   % java -cp jscheme.jar jscheme.REPL -interactive

One could also change the depth at runtime:

   > (set! jsint.Scheme.printDepth$ 10)

We could also add a global variable for controlling the type of 
debugging
output generated displayed when an exception is thrown ...

How does that sound???


---Tim---