[plt-dev] mzlib/trace better prefixes

Jon Rafkind wrote:
> Attached is a patch that changes the prefixes that mzlib/trace prints  
> depending on whether a function call is occuring or if a result is being  
> returned. "<" is a function call and ">" is a return value.

That looks backward to me: the trace library represents the stack of
function calls horizontally from left to right, so for a function call
I would expect it to use ">" to point in the direction in which the
stack grows...  I don't see anything wrong with using "|" anyway (if
it's used the right way, see below).

> I find this is easier to read than the current ambiguous "|".

I agree that the current output:

|(fact 5)
| (fact 4)
| |(fact 3)
| | (fact 2)
| | |(fact 1)
| | | (fact 0)
| | | 1
| | |1
| | 2
| |6
| 24
|120
120

could be better.  I understand why 120 appears twice but I find it a
bit confusing, and I also think it would be better to use "|" to
symbolize actual stack frames rather than just use it along with " "
for vertical alignment purposes, even if that means using twice the
amount of horizontal space to represent the stack.  Something like
this:

(fact 5)
| (fact 4)
| | (fact 3)
| | | (fact 2)
| | | | (fact 1)
| | | | | (fact 0)
| | | | | 1
| | | | 1
| | | 2
| | 6
| 24
120

or like this, if you imagine that (fact 2) is somehow a tail call:

(fact 5)
| (fact 4)
| | (fact 3)
| | (fact 2)
| | | (fact 1)
| | | | (fact 0)
| | | | 1
| | | 1
| | 6
| 24
120

Philippe