[Rd] pinning down symbol values (Scoping/Promises) question

2007-02-16 Thread Ross Boylan 
I would like to define a function using symbols, but freeze the symbols
at their current values at the time of definition.  Both symbols
referring to the global scope and symbols referring to arguments are at
issue. Consider this (R 2.4.0):
 k1 - 5
 k
[1] 100
 a - function(z) function() z+k
 a1 - a(k1)
 k1 - 2
 k - 3
 a1()
[1] 5
 k - 10
 k1 - 100
 a1()
[1] 12

First, I'm a little surprised that that the value for k1 seems to get
pinned by the initial evaluation of a1.  I expected the final value to
be 110 because the z in z+k is a promise.

Second, how do I pin the values to the ones that obtain when the
different functions are invoked?  In other words, how should a be
defined so that a1() gets me 5+100 in the previous example?

I have a partial solution (for k), but it's ugly.  With k = 1 and k1 =
100,
 a - eval(substitute(function(z) function() z+x, list(x=k)))
 k - 20
 a1 - a(k1)
 a1()
[1] 101
(by the way, I thought a - eval(substitute(function(z) function() z+k))
would work, but it didn't).

This seems to pin the passed in argument as well, though it's even
uglier:
 a - eval(substitute(function(z) { z; function() z+x}, list(x=k)))
 a1 - a(k1)
 k1 - 5
 a1()
[1] 120

-- 
Ross Boylan  wk:  (415) 514-8146
185 Berry St #5700   [EMAIL PROTECTED]
Dept of Epidemiology and Biostatistics   fax: (415) 514-8150
University of California, San Francisco
San Francisco, CA 94107-1739 hm:  (415) 550-1062

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Re: [Rd] pinning down symbol values (Scoping/Promises) question

2007-02-16 Thread Gabor Grothendieck 
See ?force

a - function(z) {
force(k)
function() z+k
}


On 2/16/07, Ross Boylan [EMAIL PROTECTED] wrote:
 I would like to define a function using symbols, but freeze the symbols
 at their current values at the time of definition.  Both symbols
 referring to the global scope and symbols referring to arguments are at
 issue. Consider this (R 2.4.0):
  k1 - 5
  k
 [1] 100
  a - function(z) function() z+k
  a1 - a(k1)
  k1 - 2
  k - 3
  a1()
 [1] 5
  k - 10
  k1 - 100
  a1()
 [1] 12

 First, I'm a little surprised that that the value for k1 seems to get
 pinned by the initial evaluation of a1.  I expected the final value to
 be 110 because the z in z+k is a promise.

 Second, how do I pin the values to the ones that obtain when the
 different functions are invoked?  In other words, how should a be
 defined so that a1() gets me 5+100 in the previous example?

 I have a partial solution (for k), but it's ugly.  With k = 1 and k1 =
 100,
  a - eval(substitute(function(z) function() z+x, list(x=k)))
  k - 20
  a1 - a(k1)
  a1()
 [1] 101
 (by the way, I thought a - eval(substitute(function(z) function() z+k))
 would work, but it didn't).

 This seems to pin the passed in argument as well, though it's even
 uglier:
  a - eval(substitute(function(z) { z; function() z+x}, list(x=k)))
  a1 - a(k1)
  k1 - 5
  a1()
 [1] 120

 --
 Ross Boylan  wk:  (415) 514-8146
 185 Berry St #5700   [EMAIL PROTECTED]
 Dept of Epidemiology and Biostatistics   fax: (415) 514-8150
 University of California, San Francisco
 San Francisco, CA 94107-1739 hm:  (415) 550-1062

 __
 R-devel@r-project.org mailing list
 https://stat.ethz.ch/mailman/listinfo/r-devel


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