a simple (commented example)

#! declare function 'test_function'
#! with return type int
#! taking an int as argument
fun int test_function(int arg) {
  #! return the argument + 2
  return arg + 2;

#! now call the function (and debug print the result)
<<< test_function(0) >>>;
#! or use alternate syntax
<<< 1 => test_function >>>;

Partial Application

According to wikipeda: In computer science, partial application (or partial function application) refers to the process of fixing a number of arguments to a function, producing another function of smaller arity.

In gwion, you can use a hole _ to achieve that

fun int test(int i, int j) {
  return i + j;

test(_, 2) @=> const auto mytest;
<<< 40 => mytest >>>;
built with mdr and mdBook
You'll find the source here, Luke! note: privacy guards may interfere with the playground