Weird feature when creating function lists with apply

# Create a function which returns a function

f1 <- function(a) {return(function(x) a*x)}

# Create a list of functions, parameterised by 1:4

apply(as.array(1:4),1,f1)[[2]](1)

[1] 4

# Repeat

f2 <- function(a) {b <- a ;return(function(x) b*x)}
apply(as.array(1:4),1,f2)[[2]](1)

[1] 2

Luke Tierney <luke at nokomis.stat.umn.edu> writes:

mkf <- function(j) function() j
for (i in 1:10) x[[i]] <- mkf(i)

That doesn't work either:

x[[2]]()

[1] 10

but for a slightly different reason: Lazy evaluation defers evaluating
the argument to mkf(i) until the funtction is called.

Argh. I've been looking at this for ten minutes and it still refuses
to sink in....

Oh, now I see it:

z<-2 ; f<-mkf(z)
z<-3
f()

[1] 3

z<-4
f()

[1] 3

The return value of mkf is not really a function of the argument, it
is the same function every time, namely the function returning "j"
which it will look up in its parent environment (the lexical one...)
when called, and only *then* will it force the promise.