[m-dev.] proposal: tracking column numbers in text streams

[Julien Fischer]

Hi,

I propose that we change io.text_input_streams so that in addition to
keeping track of the line numbers, they also keep track of the column
number.  Amongst other things this would allow us to associate column
numbers with compiler error messages (after suitably modifying the term
parser).

We can always add "fast" versions of the various I/O operations that do
not maintain the column number count, if the overhead involved is
excessive.  (Assuming there is in-principle support for this, I'll
measure the performance impact before committing anything anyway.)

Cheers,
Julien.