R type conversion [removed]) function()

Question

I\'ve been trying to write a program in R that implements Newton\'s method. I\'ve been mostly successful, but there are two little snags that have been bothering me. Here\'s m

Answer 1

1. This first problem arises because readline reads in a text string, whereas what you need is an expression. You can use parse() to convert the text string to an expression:

   f <-readline(prompt="Function? ")
   sin(x)
   f
   # [1] "sin(x)"
   
   f <- parse(text = f)
   f
   # expression(sin(x))
   
   g <- D(f, "x")
   g
   # cos(x)
   

2. To pass in values for the arguments in the function call in the expression (whew!), you can eval() it in an environment containing the supplied values. Nicely, R will allow you to supply those values in a list supplied to the envir= argument of eval():

   > eval(f, envir=list(x=0))
   # [1] 0