advice/opinion on "<-" vs "=" in teaching R

On 15-Jan-10 08:14:04, Barry Rowlingson wrote:

On Fri, Jan 15, 2010 at 6:57 AM, Ted Harding
<Ted.Harding at manchester.ac.uk>wrote:

There is at least one context where the distinction must be
preserved. Example:

?pnorm(1.5)
?# [1] 0.9331928
?pnorm(x=1.5)
?# Error in pnorm(x = 1.5) : unused argument(s) (x = 1.5)
?pnorm(x<-1.5)
?# [1] 0.9331928
?x
?# [1] 1.5

Ted.

I would regard modifying a variable within the parameters of a
function call as pretty tasteless. What does:

?foo(x<-2,x)
or
?foo(x,x<-3)

do that couldn't be done clearer with two lines of code?

?Remember: 'eschew obfuscation'.

Barry

Tasteless or not, the language allows it to be done; and therefore
discussion of distinctions between ways of doing it is relevant to
Erin's question!

While I am at it, in addition to the above example, we can have

?x <- 1.234
?sqrt(x=4)
?# [1] 2
?x
?# [1] 1.234

compared with (as in the first example):

?x <- 1.234
?sqrt(x<-4)
?# [1] 2
?x
?# [1] 4

There is a passage in ?"<-" (which I don't completely understand)
which is also relevant to Erin's query about '=' vs '<-':

?The operators '<-' and '=' assign into the environment in
?which they are evaluated. ?The operator '<-' can be used
?anywhere, whereas the operator '=' is only allowed at the
?top level (e.g., in the complete expression typed at the
?command prompt) or as one of the subexpressions in a braced
?list of expressions.

(I'm not too clear about the scope of "one of the subexpressions
in a braced list of expressions").

x = xyplot(1~1)
system.time(x = xyplot(1~1))

system.time({ x = xyplot(1~1) })