How to combine expressions in R -

i want combine expressions add them together, or division (code below), , i'm getting error:

non-numeric argument binary operator

how combination?

a=0 fun2 = expression(sin(x)) fun4 = expression(sin(pi/4)) n=1 while(n<3){   fun1 = fun2   fun2 = d(fun1,"x")   fun3 = expression(fun2/(prod(1:n)*(x-1)^n))   fun4 = expression(fun4+fun3)   n=n+1 } 

here recursive implementation build taylor expansion. result of class "call", can evaluate expression. builds expression tree, adding each additional term in taylor expansion recursively.

taylor <- function(f, a, deg, curr=null) {     if (is.function(f)) f <- body(f)  # use body of function derivatives      ## base cases     if (missing(curr))         return( as.call(list(`+`, eval(f, list(x=a)), taylor(f, a, deg, 1))) )     if (curr == deg+1) return ( 0 )      ## build each additional term     return (         as.call(list(`+`,                      as.call(list(`/`,                                   as.call(list(`*`,                                                eval(d(f, "x"), list(x=a)),                                                as.call(list(`^`, as.call(list(`-`, quote(x), a)), curr)))),                                   prod(1:curr))),                      taylor(d(f, "x"), a, deg, curr=curr+1)))     ) } 

you can see expression returns

## function, parameters f <- function(x) sin(x) <- 0  (t3 <- taylor(f, a, 3)) # .primitive("+")(0, .primitive("+")(.primitive("/")(.primitive("*")(1,  #     .primitive("^")(.primitive("-")(x, 0), 1)), 1), .primitive("+")(.primitive("/")(.primitive("*")(0,  #     .primitive("^")(.primitive("-")(x, 0), 2)), 2), .primitive("+")(.primitive("/")(.primitive("*")(-1,  #     .primitive("^")(.primitive("-")(x, 0), 3)), 6), 0)))) 

and, see if working

## @ xs <- seq(-4, 4, len=100) curve(f, -4, 4, type="p", pch=".", cex=4, main="approximations of sin(x) @ x=1",       ylim=c(-2, 2))  cols <- colorramppalette(c("orange", "red"))(7) with(list(x=xs), {     (i in 1:7)         points(xs, eval(taylor(f, a=1, i)), col=cols[i], lty=2, type="l", lwd=2) })