Comment by Ashymad

The trait system and macros run at compile time and sadly there is no way to interact with the Rust compiler. However the macro is fully incremental (creating new words too). Which means in theory if it were possible to ask for input and pass it to the macro it would behave more like a VM:

  // create a word
  forth!(: inc 1 + ;);
  // ask user for $input
  type Stack = forth!($input inc return);
  // if you keep the stack around it can be used again
  forth!({ Stack } inc .);
  // should print $input + 2