Message-ID: <494AEB6E.3010409@biostat.ku.dk>
Date: 2008-12-19T00:31:42Z
From: Peter Dalgaard
Subject: understanding recursive functions
In-Reply-To: <494AE7C1.3060504@idi.ntnu.no>
Wacek Kusnierczyk wrote:
> Wacek Kusnierczyk wrote:
>> it's a pity that <<- is not explained in ?`<<-` clearly enough:
>>
>> " The operators '<<-' and '->>' cause a search to made through the
>> environment for an existing definition of the variable being
>> assigned. If such a variable is found (and its binding is not
>> locked) then its value is redefined, otherwise assignment takes
>> place in the global environment. Note that their semantics differ
>> from that in the S language, but are useful in conjunction with
>> the scoping rules of R. See 'The R Language Definition' manual
>> for further details and examples."
>>
>>
>
> the description is further imprecise as to what happens if such a
> variable is found but is locked:
>
> foo = function() {
> x = 0
> lockBinding("x", environment())
> (function() x <<- 1)()
> unlockBinding("x", environment())
> }
>
> foo()
> # error
>
> if analysed logically (IF (found AND not locked THEN assign) ELSE assign
> globally), the description is wrong.
Yes.
If such a variable is found then its value is redefined (unless its
binding is locked), otherwise assignment take place in the global
environment.
--
O__ ---- Peter Dalgaard ?ster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907