Thanks for your recommendation !I am pretty interested in web security partly because I want to start my own start up in two years, and I want to make sure my customer's data is safe. I am also interested in compilers but just can't bear C++, so I plan to take this course :https://www.coursera.org/learn/nand2tetris2. It doesn't limit languages you can use .So I plan to write the compiler by Racket(which can also sharpen my functional programming skill).