R help - Sep 2012 - eval and tcltk : target of assignment expands to non-language object

Hi everyone,

I have a problem to assign a value with tcl/tk

ths is the code ( it should be simple to understand) :

library(tcltk)

valA<-tclVar("0")
valB<-tclVar("0")
valC<-tclVar("0")
id<-"A"
out<-"1"
out2<-"2"

print(paste("tclvalue(val",id,")",sep="")) # ok
print(as.name(paste("tclvalue(val",id,")",sep="")))
#ok
print(eval(as.name(paste("val",id,sep="")))) #seems to be OK
print(tclvalue(eval(as.name(paste("val",id,sep=""))))) #ok
print("fin")

tclvalue(valA)<-out # this is good
tclvalue(valA)
tclvalue(paste("val",id,sep="")) #dont work but its normal
tclvalue(as.name(paste("val",id,sep="")))# dont work...
eval(as.name(paste("val",id,sep="")))# ok
tclvalue(eval(as.name(paste("val",id,sep=""))))#ok
is(eval(as.name(paste("val",id,sep=""))))

#that is what I want to do but it dont work :
tclvalue(eval(as.name(paste("val",id,sep=""))))<-out2
#>target of assignment expands to non-language object

# Have you any idea to do what I want to do?

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On Sep 24, 2012, at 10:27 , vincent guyader wrote:
> Hi everyone,
> 
> I have a problem to assign a value with tcl/tk
Not really. You'll get into the same sort of trouble if you try other kinds
of complex assignments:
> a <- 1:2
> eval(as.name("a"))[[1]]
[1] 1
> eval(as.name("a"))[[1]] <- 3
Error in eval(as.name("a"))[[1]] <- 3 : 
  target of assignment expands to non-language object

This is similar to Lumley's fortune("parse"): You may want to
rethink the question. Wouldn't

l <- list(A=tclVar("0"), B=tclVar("0"),
B=tclVar("0"))
...
tclvalue(l[[id]]) <- ....

do the job much neater?

However if you insist, I suspect you need to use bquote() and an outer eval(),
as in

eval(bquote(.(as.name("a"))[[1]] <- 3))
> 
> ths is the code ( it should be simple to understand) :
> 
> library(tcltk)
> 
> valA<-tclVar("0")
> valB<-tclVar("0")
> valC<-tclVar("0")
> id<-"A"
> out<-"1"
> out2<-"2"
> 
> print(paste("tclvalue(val",id,")",sep="")) #
ok
>
print(as.name(paste("tclvalue(val",id,")",sep="")))
#ok
> print(eval(as.name(paste("val",id,sep="")))) #seems to
be OK
> print(tclvalue(eval(as.name(paste("val",id,sep="")))))
#ok
> print("fin")
> 
> tclvalue(valA)<-out # this is good
> tclvalue(valA)
> tclvalue(paste("val",id,sep="")) #dont work but its
normal
> tclvalue(as.name(paste("val",id,sep="")))# dont work...
> eval(as.name(paste("val",id,sep="")))# ok
> tclvalue(eval(as.name(paste("val",id,sep=""))))#ok
> is(eval(as.name(paste("val",id,sep=""))))
> 
> #that is what I want to do but it dont work :
>
tclvalue(eval(as.name(paste("val",id,sep=""))))<-out2
> #>target of assignment expands to non-language object
> 
> # Have you any idea to do what I want to do?
> 
> 	[[alternative HTML version deleted]]
> 
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-- 
Peter Dalgaard, Professor,
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