Create `R_src`

Create the directory R_src.
For each function create a directory named as the function, like R_src/f1/ and R_src/f2/.
Put the main R functions in that directories, i.e.R_src/f1/f1.R and R_src/f2/f2.R.
Create the directory main/ in each function directory, like R_src/f1/main/ and R_src/f2/main/.
In each main/ directory create an R script. Its name should be main.R. (R_src/f1/main/main.R and R_src/f2/main/main.R)
Each main.R includes a minimum example for its function. As an example, the following script is for the function f1.R:

source('../f1.R')
f1(1,2)

Link `*.R` files to `R/`

The library roxygen2 should be installed. Then, run the bash script roxygenize.sh to install the package.

Run the bash script install.sh to install the package.