Zion generic function application example

apply-f.zion

module _

fn square(x any T) any T {
  return x * x
}

fn apply(f (fn(y any T) any T), x any T) any T {
  return f(x)
}

fn main() {
    print(apply(square, 2))
}

output.txt

program.zion:3:4: error: we don't have enough info to instantiate this function
program.zion:11:4: while checking main : fn _() ()
program.zion:11:4: error: failures encountered

The issue here is that square is not yet reified as a bound variable, so at the point that the reference to square is made on line 12, the compiler doesn't know how to instantiate it. This is either a weakness in the language or the compiler, I think the compiler. The deeper issue is the resolution of function definitions as symbols in the context of an expression evaluation. You should try to come up with a way to do the book keeping to allow unchecked functions (basically any function definition with free type variables) to be treated like function literals are treated. Then I bet this would just work. https://github.com/zionlang/zion/blob/master/src/type_checker.cpp#L1000