R help - Dec 2004 - Detecting incomplete commands

Hello,

I need a similar behaviour as with the prompt: asking to complete incomplete
R command with eval(parse(text = ....))
Is it a way to make the difference between an illegal and an incomplete R
command in a string?
For instance:
> parse(text="ls()")
expression(ls())

This is fine!
> parse(text="ls(")
Error in parse(file, n, text, prompt) : parse error

This is an incomplete command, and I want to ask to the user for further
input (multiline command)
> parse(text="ls())")
Error in parse(file, n, text, prompt) : parse error

This is clearly an illegal command. Could I make a distinction with the
previous case here?
Best,

Philippe Grosjean

..............................................<??}))><........
 ) ) ) ) )
( ( ( ( (    Prof. Philippe Grosjean
 ) ) ) ) )
( ( ( ( (    Numerical Ecology of Aquatic Systems
 ) ) ) ) )   Mons-Hainaut University, Pentagone
( ( ( ( (    Academie Universitaire Wallonie-Bruxelles
 ) ) ) ) )   6, av du Champ de Mars, 7000 Mons, Belgium  
( ( ( ( (       
 ) ) ) ) )   phone: + 32.65.37.34.97, fax: + 32.65.37.33.12
( ( ( ( (    email: Philippe.Grosjean at umh.ac.be
 ) ) ) ) )      
( ( ( ( (    web:   http://www.umh.ac.be/~econum
 ) ) ) ) )
..............................................................

Philippe Grosjean wrote:
> Hello,
> 
> I need a similar behaviour as with the prompt: asking to complete
incomplete
> R command with eval(parse(text = ....))
> Is it a way to make the difference between an illegal and an incomplete R
> command in a string?
> For instance:
> 
> 
>>parse(text="ls()")
> 
> expression(ls())
> 
> This is fine!
> 
> 
>>parse(text="ls(")
> 
> Error in parse(file, n, text, prompt) : parse error
> 
> This is an incomplete command, and I want to ask to the user for further
> input (multiline command)
Hello Phillipe,

why not using something like this:

 > ok<-try(parse(text="ls("), silent=TRUE)
 > ok
[1] "Error in parse(file, n, text, prompt) : parse error\n"
attr(,"class")
[1] "try-error"

and then check if "ok" is an expression:

 > is.expression(ok)
FALSE


Thomas P.

Thank you Thomas for your answer. This is of course what I intend to do
(indeed, to use a tryCatch(), instead of I try(). However, I would like to
have a different behaviour depending if the synthax is incorrect
"ls())" for
instance, or incomplete "ls(" for instance. Indeed, exactly like the
distinction made at the command line:
> ls()) # This generates an error
Error: syntax error
> ls( # This is not an error, but a multiline command
+ 

If you use parse() within a try(), you got the same error message in both
cases: "Error in parse(file, n, text, prompt) : parse error". So, it
is not
possible to discriminate between the two situation in this context. Is it a
way to cope with that?

Best,

Philippe Grosjean 
  
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Thomas Petzoldt
> Sent: Thursday, December 16, 2004 3:18 PM
> To: phgrosjean at sciviews.org
> Cc: r-help at stat.math.ethz.ch
> Subject: Re: [R] Detecting incomplete commands
> 
> Philippe Grosjean wrote:
> > Hello,
> > 
> > I need a similar behaviour as with the prompt: asking to complete 
> > incomplete R command with eval(parse(text = ....)) Is it a 
> way to make 
> > the difference between an illegal and an incomplete R command in a 
> > string?
> > For instance:
> > 
> > 
> >>parse(text="ls()")
> > 
> > expression(ls())
> > 
> > This is fine!
> > 
> > 
> >>parse(text="ls(")
> > 
> > Error in parse(file, n, text, prompt) : parse error
> > 
> > This is an incomplete command, and I want to ask to the user for 
> > further input (multiline command)
> 
> Hello Phillipe,
> 
> why not using something like this:
> 
>  > ok<-try(parse(text="ls("), silent=TRUE)  > ok [1]
"Error
> in parse(file, n, text, prompt) : parse error\n"
> attr(,"class")
> [1] "try-error"
> 
> and then check if "ok" is an expression:
> 
>  > is.expression(ok)
> FALSE
> 
> 
> Thomas P.
> 
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