Looping through an array like structure in LaTeX

In python, and in most other programming languages I am familiar with, I can assign values to an array-like data structure, loop through each element and pass the element to a function on each iteration. Here's an example:

def f(x):
  return "This is {}".format(x)

if __name__=="__main__":
  x = ['param1', 'param2', 'param3']

  for item in x:
    print(f(item))

Running the above will print the following to standard output:

This is param1
This is param2
This is param3

There are several advantages to this:

I only have to call the function f once
I can nest an additional for loop for every parameter in my function f

Recently I have been playing around with plain TeX, and I understand that TeX is a macro oriented, expansion based language. The closest thing I could get to the above was this:

\def\f#1{This is #1 \par}

\f{param1}
\f{param2}
\f{param3}

\end

This is suboptimal because:

I have to call the command \f multiple times
I have to call it with a different parameter each time.

Is there anything I can do to refactor the above TeX code to something more DRY? How can I emulate an array like structure and a for each loop in Plain TeX?

Solution

In latex, you could use the pgffor package:

\documentclass{article}

\usepackage{pgffor}

\begin{document}

\foreach \x in {param1, param2, param3}{
  This is \x\par
}

\def\foo{param1, param2, param3}
\foreach \x in \foo {
  This is \x\par
}

\end{document}