R-beta: calling R from FORTRAN

[Thomas Lumley]

There was a question earlier today, on either r-help or r-devel, about
calling R code from FORTRAN (I deleted it accidentally, so I don't know
which list it belonged to).

Anyway, there is a workaround to call R functions from FORTRAN which is
used in the "integrate" library. It was invented for S by Mike Meyer.  The
FORTRAN code needs to be written to call a fixed C function and pass it a
pointer to the R function. The C function then uses call_S to call the R
function. 

As everything is passed by reference in FORTRAN the argument is
automatically a pointer. Since the FORTRAN code never does anything with
the pointer except pass it, you can declare the argument to have any type
you like. "integrate" declares the function pointer to be DOUBLE
PRECISION. In principle on some machines there could be alignment issues,
but this would only be a problem if the FORTRAN compiler insisted on
checking the alignment of a pointer it never dereferenced.



Thomas Lumley
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