R - Binding values to a symbol

• Scoping: Binding values to a symbol
• If we define a function named "mean", how R will recognize it? 

 > mean <- function(x,y){  
 +   x+y  
 + }  
 > mean(1,4)  # it will search mean from user environment (or global environment) first
 [1] 5  
 > search()  # check search order in R
  [1] ".GlobalEnv"    "tools:rstudio"   "package:stats"   "package:graphics" "package:grDevices"  
  [6] "package:utils"   "package:datasets" "package:methods"  "Autoloads"     "package:base"    

• Free variable, the variable is searched from environment in which the function is defined(Lexical Scoping).
• If can't find in the environment, search top-level environment (workspace, packages)

 > z <- 11  
 > fun <- function(x,y){  
 +   x+y-z  # z is a free variable here
 + }  
 > fun(12,13)  
 [1] 14  

• Define function inside a function

 > make.power <- function(n){  
 +   pow <- function(x){  
 +     x^n  
 +   }  
 +   pow  
 + }  
 > cube <- make.power(3)  
 > cube(2)  
 [1] 8  
 > ls(environment(cube))  # list what in function closure (environment)
 [1] "n"  "pow"  
 > get("n",environment(cube))  # get value of n
 [1] 3  
 > get("pow",environment(cube))  # get value of pow
 function(x){  
     x^n  
   }  
 <environment: 0x000000000856e658>  

• Lexical Scoping and Dynamic Scoping(searched from environment in which the function is called)

 > a <- 1  
 > f <- function(b){  
 +   a <- 10  
 +   a + b + g(b)  # a is 10 in f() and 1 in g(b) since R is using lexical scoping, a is 10 in g(b) if it is Dynamic Scoping 
 + }  
 > g <- function(b){  
 +   a + b  
 + }  
 > f(1)  
 [1] 13  

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