[R] Question about expression parser for "return" statement

[Duncan Murdoch]

On 13/11/2016 9:42 PM, Jeff Newmiller wrote:
> I find your response here inconsistent... either including `return` causes a "wasted" function call to occur (same result achieved slower) or the parser has an optimization in it to prevent the wasted function call (only behaviorally the same).

I don't understand what you are finding inconsistent.  I wasn't talking 
about wasting anything.  I was just saying that expressions like

return (a)*b

are evaluated by calling return(a) first, because return() is a 
function, and then they'll never get to the multiplication.

BTW, there don't appear to be many instances of this particular bug in 
CRAN packages, though I don't have a reliable test for it yet.  The most 
common error seems to be using just "return", as mentioned before.  The 
fix for that is to add parens, e.g. "return()".  The next most common is 
something like

invisible(return(x))

which returns x before making it invisible.  The fix for this is to use

return(invisible(x))


> I carefully avoid using the return function in R. Both because using it before the end of a function usually makes the logic harder to follow and because I am under the impression that using it at the end of the function is a small but pointless waste of CPU cycles. That some people might be prone to writing a C-like use of "return;" which causes a function object to be returned only increases my aversion to using it.

Sometimes it is fine to use return(x), but it shouldn't be used routinely.

Duncan Murdoch

> -- Sent from my phone. Please excuse my brevity. On November 13, 2016
> 3:47:10 AM PST, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
>> >On 13/11/2016 12:50 AM, Dave DeBarr wrote:
>>> >> I've noticed that if I don't include parentheses around the intended
>> >return
>>> >> value for the "return" statement, R will assume the first
>> >parenthetical
>>> >> expression is the intended return value ... even if that
>> >parenthetical
>>> >> expression is only part of a larger expression.
>>> >>
>>> >> Is this intentional?
>> >
>> >Yes, return is just a function call that has side effects.  As far as
>> >the parser is concerned,
>> >
>> >return ((1/sqrt(2*pi*Variance))*exp(-(1/2)*((x - Mean)^2)/Variance))
>> >
>> >is basically the same as
>> >
>> >f((1/sqrt(2*pi*Variance))*exp(-(1/2)*((x - Mean)^2)/Variance))
>> >
>> >Duncan Murdoch