Make monadsyntax more aware of print depth

[hrutvik]

Limiting print depth has an unusual effect on long monadic definitions, because all monadic assignments on the top-level "spine" of binds are printed at the same depth. This commit attempts to reduce the print depth further down the spine, so that later assignments are elided.

[mn200]

If I understand you right, you're complaining about the fact that you might get output like:

  do
    v1 <- ... ; 
    v2 <- ... ; 
    v3 <- ... ; 
od

where you'd prefer to see, e.g.:

do 
   v1 <- ...; 
   ...
od

I'm not so sure about this, and may well have deliberately written the print-depth decrementing code to achieve the first effect. I have certainly found it annoying when list-forms are printed so as to lose the information about how many elements there are in a list. But equally, if the list/do-form is a million elements long, having to see them all when you've gone to the trouble of specifying a depth of 10 is a bit user-hostile. I also dislike the way that when printing lists you get a “triangular” decay so that later elements, if they are printed, get printed with less detail. Perhaps the logic could be that you don't get any more than depth elements printed, and that each element is printed with depth-1.

[binghe]

In the world of Lisp, there's the difference between *print-length* and *print-level* (depth) [1] when printing lists (s-expressions).

[1] https://www.lispworks.com/documentation/HyperSpec/Body/v_pr_lev.htm#STprint-lengthST

[mn200]

@binghe That's interesting! Perhaps we should adopt something similar.

[hrutvik]

Apologies @mn200, yes that example is the kind of thing I'm referring to (specifically the situation with very many elements in the list/do-form). I can see that having both behaviours could be useful - following @binghe's suggestion perhaps I can add a notion of "print length" as a separate reference in monadsyntax, which can then be set by the user?

[mn200]

Thanks for getting this underway! Can you move the reference to the Globals structure to sit alongside the existing print_depth variable? I can then use it in the system’s printing of other “list forms” (sets, lists, records, let-bindings).

[mn200]

Thanks!