Roger Bivand wrote:
> On Thu, 15 May 2008, Barry Rowlingson wrote:
>
>> Duncan Murdoch wrote:
>>
>>> It's fairly unlikely to go away, but it's an old undocumented
>>> feature, so
>>> use at your own risk. There are lots of other undocumented
>>> features, but
>>> maybe no others at the lexical level. Check out src/main/gram.y if
>>> you
>>> want to search for more at that level, and src/* if you want them
>>> at any
>>> level.
>>
>>
>> I just had a quick browse in the source and I can't see where "**" is
>> defined. names.c relates ^ to the power operation in arithmetic.c but
>> no sign of "**":
>>
>> ./names.c:{"^", do_arith, POWOP, 1, 2,
>> {PP_BINARY2, PREC_POWER, 1}},
>>
>> grepping for POWOP doesn't help.
>>
>> It's not an operator like '*':
>>> get("**")
>> Error in get("**") : variable "**" was not found
>>> get("*")
>> function (e1, e2) .Primitive("*")
>>
>> and there's no ** in gram.y.
>>
>> searching for 'power' and quoted "**" doesn't help me either.
>> Searching for unquoted ** just produces too much C code to be useful.
>>
>> It's got to be there somewhere!!!
>
> Is there a clue in:
>
>> "^"(5, 2)
> [1] 25
>> "**"(5, 2)
> Error: could not find function "**"
>> 5 ^ 2
> [1] 25
>> 5 ** 2
> [1] 25
>
> that is, it is truly obfuscated and not accessible using contemporary
> interfaces?
Not really, just transcribed during the lexical analysis phase:
case '*':
if (nextchar('*'))
c='^';
yytext[0] = c;
yytext[1] = '\0';
yylval = install(yytext);
return c;
(There's no "->" function either...)
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907
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