Functions returning functions

Paulo Grahl wrote:

Dear All:

I have a question regarding the behavior of functions.
Say I define a function that returns another function :
A <- function(parameters) {
? ? # calculations w/ parameters returning 'y'
? ? tmpf <- function(x) { # function of 'y' }
? ? return(tmpf)
}

The value of the parameters are stored in an environment local to the
function. Then I call
x<- something
B<-A(x)

When R executes this last statement, ?does it perform all the
calculations inside function A again

no, see this:

f <- function( x = 3){

+ ? ?function( ){}
+ }

g <- f()
ls.str( environment(g) )

x : ?num 3

h <- f(6)
ls.str( environment(h) )

x : ?num 6

ls.str( environment(g) )

x : ?num 3

See also colorRampPalette which uses this feature:

colorRampPalette

function (colors, ...)
{
? ramp <- colorRamp(colors, ...)
? function(n) {
? ? ? x <- ramp(seq.int(0, 1, length.out = n))
? ? ? rgb(x[, 1], x[, 2], x[, 3], maxColorValue = 255)
? }
}
<environment: namespace:grDevices>

pal <- colorRampPalette( c("blue", "white", "red") )
pal

function (n)
{
? x <- ramp(seq.int(0, 1, length.out = n))
? rgb(x[, 1], x[, 2], x[, 3], maxColorValue = 255)
}
<environment: 0x99aba4c>

ls.str( environment( pal ) )

colors : ?chr [1:3] "blue" "white" "red"
ramp : function (x)

(i.e., all the calculations that
yield 'y')
?or the value of 'y' is already stored in the function's local environment
?

Many thanks.
Paulo Gustavo Grahl, CFA

--
Romain Francois
Independent R Consultant
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr