In a forth-like language, you can think of all functions as implicitly being unary: They take a stack, and return a stack. I've never used any other kind of co

In a forth-like language, you can think of all functions as implicitly being unary: They take a stack, and return a stack. I've never used any other kind of concatenative language, so I'm less able to speak to them, but I'm guessing some similar situation applies for those as well.