[R] RE: [Rd] too many arguments in foreign function call

Peter Dalgaard BSA p.dalgaard at biostat.ku.dk
Mon Jul 16 23:14:01 CEST 2001

Duncan Murdoch <murdoch at stats.uwo.ca> writes:

> On Mon, 16 Jul 2001 19:23:52 +0100 (GMT Daylight Time), you wrote in
> message <Pine.WNT.4.31.0107161916001.1056-100000 at tern.stats>:
> >The argument is that new code should probably be using .Call (if S
> >compatibility is relevant) or .External rather than .C, at least provided
> >that a C wrapper is feasible.  Those interfaces seem very much under-used.
> >(Including by me, for S3-compatibility reasons.)
> The difficulty with using .External is that it only works with C, not
> with other languages, because you need the R header definitions.  I
> think there is a fairly large group of programmers like myself who
> aren't very comfortable programming in C.  The .C interface isn't tied
> to the R header files the way .External is, so it's not too hard to
> call other languages with it.  I use it with Delphi and Kylix, for
> instance.
> It's a nice quirk that ".C" is the interface to use for general
> external code, and ".External" for C code.

That's a coincidence, highly dependent on other languages abiding the
C calling conventions (and arguably, .External is really interfacing
to a Scheme-like runtime system rather than general C code...)

It's like Brian says: If you can figure out how to call the other
language from C, then it really shouldn't be any trouble to setup a
wrapper using either of the interfaces .C, .Call, and .External. And
given that you usually need "onionskin" routines to convert pointer
arguments for call-by-value usage, the extra work of zipping a bunch
of scalar arguments out of a vector does seem rather minute.

   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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