[R] boolean SEXP interpretation upon function return

[Prof Brian Ripley]

On Fri, 5 Aug 2011, Duncan Murdoch wrote:

> On 11-08-05 12:09 AM, Alexandre Aguiar wrote:
>> Hi,
>> 
>> When a function returns a SEXP of type LGLSXP (logical) to signal whether
>> it succeeded or failed, how is it intrepreted? Is it like C where SUCCESS
>> = 0 or other value?
>
> Usually TRUE is used to signal success.  TRUE is non-zero.

Strictly, TRUE is not numeric: it is coerced to 1 when coerced to a 
numeric value.

If you are looking at C level at the SEXP: don't as the internal 
representation is just that: 'internal and subject to change'.

There is no C convention to use 0 for success: that is a Unix 
convention for status values as returned by exit(), and even there the 
man page will advise you to use the symbol EXIT_SUCCESS.  Other OSes 
do differ.

>
> Duncan Murdoch
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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