R devel - Jul 2001 - bug in eval

Is this a bug ?

> foo <- function(a, ...)
+ {
+     tl <- substitute(list(a=a))
+ 
+     ## the foll two should give the same results
+     ## according to defaults for eval
+     
+     print(eval(tl ))
+     print(eval(tl, parent.frame()))
+ }
> 
> 
> foo1 <- function(...)
+ {
+     foo(...)
+ }
> 
> test <- function(a = 6)
+ {
+     foo1(a = a)
+ }
> 
> test(10)
$a
[1] 10

Error in eval(expr, envir, enclos) : Object "a" not
found
> 
> str(eval)
function (expr, envir = parent.frame(), enclos = if (is.list(envir) || 
    is.pairlist(envir)) parent.frame())  
> 


I'm having similar problems with 

eval(expr, data, parent.frame()) # doesn't work

and

eval(expr, data) # works

where data is a data frame.

Deepayan

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Deepayan Sarkar <deepayan@stat.wisc.edu> writes:
> Is this a bug ?
> 
> 
> > foo <- function(a, ...)
> + {
> +     tl <- substitute(list(a=a))
> + 
> +     ## the foll two should give the same results
> +     ## according to defaults for eval
> +     
> +     print(eval(tl ))
> +     print(eval(tl, parent.frame()))
> + }

Nope. This is not a bug, just confusing. The thing to note is that
default expressions are evaluated in the frame of the called function.
I.e. the parent.frame() referred to as the default for envir in eval()
is the caller of eval, whereas in eval(expr, parent.frame()) the
parent.frame() is evaluated in the callers frame, giving you the
grandparent of the eval call.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
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