[metapost] make_text related scanning improvements

[Marcel Krueger]

 ---- On Fri, 18 May 2018 11:32:57 +0200 Hans Hagen <j.hagen at xs4all.nl> wrote ---- 
 > On 5/18/2018 11:22 AM, Taco Hoekwater wrote:
 > > Hi,
 > > 
 > >> On 18 May 2018, at 11:15, Hans Hagen <j.hagen at xs4all.nl> wrote:
 > >>
 > >> changing fundamentals like this nearly always have side effects ... you cannot always know how these tools are used (for decades) ... you solve one problem and introduces a new one .. such is the world of tex / mp
 > > 
 > > As the original ‘author’ of the reimplementation I can attest to that!
 > > 
 > > It took half a dozen minor adjustments to the reimplementation just to make it compatible with pre-existing metapost source files, due to subtle differences between the Pascal and C handling of whitespace. I am not saying the code cannot be improved at all, but it seems likely that any changes at this point will have side-effects that break already existing metapost source files.
 > right, so
 > 
 >    btex ... etex
 > 
 > will stay as it is, but i'll look if
 > 
 >    verbatimtex ... etex
 > 
 > can optionally (!) deal with newlines

Awesome.
Regarding breaking existing `make_text` callbacks by allowing newlines: As far as I can tell a make_text callback should already be able to deal with newlines in the passed string, because the current version already allows a user to do something like

    maketext("abc" & char10 & "def")

Anyway, thank you very much for your feedback.

Marcel