Port of R header files to Delphi

I'm in the process of porting R header files to Delphi.  The short
term aim is to be able to make calls into the R.dll from Delphi; the
longer term aim is to play around with writing a Windows front-end
with some of the features of the S-PLUS environment (e.g. scripts),
and other features from other IDEs I've used (e.g. watch windows,
popup values of variables selected by mouse, etc.)

I've got a port of the simple rterm.c sample front-end sort of
working, but I need lower level access, and I'm having trouble getting
any further.  Is this the place to ask technical questions on this, or
should I ask somewhere else (or just not bug everyone, since I'm not
working on Unix or in C)?

I suspect it is the best place, as most of your questions are about
R internals.  As for the R for Windows internals, probably only Guido 
knows, but you can read the code as I have to frequently.

For example:

1.  Syntax errors are causing my rterm to shut down, apparently
because I'm not catching the exceptions that are thrown.  How are
exceptions thrown?

I suspect that is just because you are not set up to run in interactive
mode (the internal variable R_Interactive).  The default error handler
does abort on error in non-interactive mode.  I don't know what your
`rterm' is, but rtest.c is specifically in non-interactive mode.
The real rterm.c sets R_Interactive based on isatty(0) and the --ess flag.
If you set interactive mode, you will need some way to interrupt,
and with a Windows front-end, the easiest way is to set UserBreak to
non-zero (which is equivalent to Ctrl-C on Unix or Esc in Rgui).

On my TODO list is to run more threads, so that there is a control
thread different from the one running the R interpreter.  Principally
to make interruption easier to handle, and to allow looping C code
to be interrupted.

2.  If I want to get R to give me a string showing how an existing
variable would be printed, what's the normal procedure?  I tried
calling "PrintValue", passing it the Rinternals export
"R_LastvalueSymbol", but I just get an access violation in R.DLL.

That's a symbol, not a variable.  Section 3.6.7 of `Writing R Extensions'
may help: the key is to use findVar or one of the related functions.

This could be because I'm not handling the export properly (DLLs
normally export entry points, not pointers to variables, so I had to
try to guess what indirection was being used here).  

Um. DLLs often export both.  Unfortunately, the mechanisms for *imports*
are messy, especially for exported pointers.  You need to refer to them as
_imp___blah, and that's purpose of globalvar.h.  There is no extra
indirection: apart from the name mapping they are handled just like
externs to other modules not in Dlls.

Or I could be
calling PrintValue at the wrong time.  Or something else.  How much
needs to be set up in advance before PrintValue will work?

PrintValue can be called on a SEXP pointing to an R object: you may find
R_PV a little safer. (Both are in src/main/print.c.)  You will need
R_WriteConsole set up, of course.

Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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