> dynamic languages don't require you to "emulate the compiler" in your head

On the contrary. Your ‘functional’ timer function takes an argument and applies the - operator to it.

You must be sure, every time you call the function, that you pass an argument to which - can be applied. If you don't, your user might see a TypeError. So you, the human author of the code, must ‘emulate the compiler’ by performing type inference and type checking in your head.

In my statically-typed language, the compiler ensures that my program only ever passes arguments for which the - operator is applicable. I don't need to ‘emulate the compiler’, because I'm actually using a compiler.