R help - Aug 1999 - text(x,y,expression(sqrt(txt))), where txt is a text string

My question was supposed to have been (I had plot() instead of text()!)
  I have e. g. 
  > txt <- "abcd"

  In
  > text(x,y, expression(sqrt(txt)))
  I want txt to be evaluated, i. e. to get sqrt(abcd) plotted,
  (with the square root symbol replacing sqrt, of course).
  Is there a way to achieve this?


Berwin Turlach provided the following:
> txt <- "abcd"
> text(4.5,4.5,as.expression(substitute(sqrt(txt),list(txt=txt))))

Bill Venables made another suggestion:

i. e. 

  > txt <- as.name("abcd")
  > ex <- expression(sqrt(txt))
  > ex
  expression(sqrt(txt))
  > ex[[1]][[2]] <- eval(ex[[1]][[2]])
  > ex
  expression(sqrt(abcd))
  >

  I think what you want in the driver's seat is a name object, not a text
  string.  Evaluating the name of a name object gives you a name, if I make
  myself clear....

One then invokes text(x,y,ex)


Neither of these seem to work in 0.64.2

Thanks for the prompt helpful responses.

John Maindonald               email : john.maindonald at anu.edu.au        
Statistical Consulting Unit,  phone : (6249)3998        
c/o CMA, SMS,                 fax   : (6249)5549  
John Dedman Mathematical Sciences Building
Australian National University
Canberra ACT 0200
Australia
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