// `sum` should be called either:
//
// - a function: `sum(...)` for compile-time errors
// - a funcref: `@sum.call(...)` for run-time errors
// - an expression: `(@sum)(...)` for run-time errors
//
print( ( sum )( 1, 2 ) );

function sum( a, b )
  return a + b;
endfunction