[R] Function that operates on functions: it's ok, but the display isn't

[Duncan Murdoch]

On 10/10/2006 3:53 PM, Alberto Monteiro wrote:
> The following code works fine:
> 
> # g is the function that returns the square of a number
> g <- function(y) y^2
> 
> # f1 is a function that takes one function
> # as argument, and returns another function
> f1 <- function(f) function(x) f(x+1) - f(x)
> 
> # h(x) is g(x+1) - g(x) or 2x + 1
> h <- f1(g)
> 
> # h(1) = 3
> # h(2) = 5
> # h(3) = 7
> 
> So far, so good. But why:
> 
> h
> 
> shows:
> 
> function(x) f(x+1)-f(x)
> <environment: 0264BE84>
> 
> I don't get it. h should show function(x) g(x+1)-g(x)
> or something like that.

But you defined the result of f1 to be function(x) f(x+1) - f(x), so 
what it is showing you is correct.  This will be evaluated in 
<environment: 0264BE84>, where f is defined to be function(y) y^2, which 
is why h gives the right answers.

Remember that R isn't a macro language, function calls aren't text 
substitutions.

Duncan Murdoch

> 
> Alberto Monteiro
> 
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