[R] What is a 'closure'?

[peter dalgaard]

On Jan 19, 2012, at 21:39 , Ben Bolker wrote:

> Ajay Askoolum <aa2e72e <at> yahoo.co.uk> writes:
> 
>> 
>> Michael, thank you, especially for the link. I think I understand.
>> 
>> The vocabulary is so different! I know 'closure' as 'user-defined function'.
>> 
> 
>  Not quite.  All (??) user-defined functions are closures, but lots
> of non-user-defined functions are closures too ...
> 

Also, it is not actually the function that is the closure, it is the function completed with its environment, which is where, during evaluation, unbound objects will be sought.

The function itself is a parsed version of the function definition. When called, almost all functions will need to find something from their environment, e.g. the "<-" operator. The only functions that are completely self-contained are those that return a constant or one of the function arguments (maybe a few more). 

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com