R help - Apr 2005 - How to extract function arguments literally

Dear all,

One of my friends asked me if it is possible to extract actual R
function arguments literally (precisely, as strings). The reason is
simple. He feels sometimes awkward to attach quotation marks :-). What
he actually wants is to pass R command arguments to XLisp subroutines
(He has been an enthusiastic XLisp user for a long time and still tends
to use R as a wrapper to XLisp). Is it possible, or should I advise him
not to be so lazy? The following is his simple example to explain the
situation.

R function "lc" which passes its argument to an Xlisp function:

 lc=function(cmd){
    cmd=as.character(substitute(cmd))
    .XLisp("lcommand", cmd)}

Corresponding XLisp function "lcommand":

 (defun lcommand (str) (eval (with-input-from-string (s str) (read s))))

If the argument cmd is a string (i.e. with quotation marks) or has no
space, it works fine.
> as.character(substitute(abc))
[1] "abc"

But, if it has no quotation marks or contains spaces, it yileds an error.
> as.character(substitute((def x1 x2))
Error: syntax error

He wants to use the syntax like lc((def x1 x2)), not like
lc("(def x1 x2)").

Thanks in advance.

=============================================================Shigeru MASE
<mase at is.titech.ac.jp>
        Tokyo Institute of Technology
        Dept. of Math. and Comp. Sciences
        O-Okayama 2-12-1-W8-28, Tokyo, 152-8550, Japan

instead of as.character(substitute(arg)) use deparse(substitute(arg))

: -----Original Message-----
: From: r-help-bounces at stat.math.ethz.ch 
: [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Shigeru Mase
: Sent: Saturday, 30 April 2005 1:24 PM
: To: r-help at stat.math.ethz.ch
: Subject: [R] How to extract function arguments literally
: 
: 
: Dear all,
: 
: One of my friends asked me if it is possible to extract actual R
: function arguments literally (precisely, as strings). The reason is
: simple. He feels sometimes awkward to attach quotation marks :-). What
: he actually wants is to pass R command arguments to XLisp subroutines
: (He has been an enthusiastic XLisp user for a long time and 
: still tends
: to use R as a wrapper to XLisp). Is it possible, or should I 
: advise him
: not to be so lazy? The following is his simple example to explain the
: situation.
: 
: R function "lc" which passes its argument to an Xlisp function:
: 
:  lc=function(cmd){
:     cmd=as.character(substitute(cmd))
:     .XLisp("lcommand", cmd)}
: 
: Corresponding XLisp function "lcommand":
: 
:  (defun lcommand (str) (eval (with-input-from-string (s str) 
: (read s))))
: 
: If the argument cmd is a string (i.e. with quotation marks) or has no
: space, it works fine.
: 
: > as.character(substitute(abc))
: [1] "abc"
: 
: But, if it has no quotation marks or contains spaces, it 
: yileds an error.
: 
: > as.character(substitute((def x1 x2))
: 
: Error: syntax error
: 
: He wants to use the syntax like lc((def x1 x2)), not like
: lc("(def x1 x2)").
: 
: Thanks in advance.
: 
: =============================================================: Shigeru MASE
<mase at is.titech.ac.jp>
:         Tokyo Institute of Technology
:         Dept. of Math. and Comp. Sciences
:         O-Okayama 2-12-1-W8-28, Tokyo, 152-8550, Japan
: 
: ______________________________________________
: R-help at stat.math.ethz.ch mailing list
: https://stat.ethz.ch/mailman/listinfo/r-help
: PLEASE do read the posting guide! 
: http://www.R-project.org/posting-guide.html
:

Shigeru Mase wrote:
> But, if it has no quotation marks or contains spaces, it yileds an error.
> 
> 
>>as.character(substitute((def x1 x2))
> 
> 
> Error: syntax error
> 
> He wants to use the syntax like lc((def x1 x2)), not like
> lc("(def x1 x2)").
No, that wouldn't be possible.  Since lc((def x1 x2)) is not legal S 
language, the parser is going to complain about it.  The only solution 
here would be to parse the whole thing yourself (i.e. parse the R 
source), rather than using the R parser.

Duncan Murdoch

Shigeru Mase <mase at is.titech.ac.jp> writes:
> But, if it has no quotation marks or contains spaces, it yileds an error.
> 
> > as.character(substitute((def x1 x2))
> 
> Error: syntax error
> 
> He wants to use the syntax like lc((def x1 x2)), not like
> lc("(def x1 x2)").
This is not possible. R expressions must follow R syntax.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
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