> but we don't usually call that "knowing what it will do", unless you can actually predict the state, or in the case of a program, the output. Who is 'we'? An

> but we don't usually call that "knowing what it will do", unless you can actually predict the state, or in the case of a program, the output. Who is 'we'? And yes, we can predict exactly what the output of a given program for a given input is, for the vast majority of cases. All you have to do is run the program. > The mere fact that compilers exist is a meaningless form of "knowing what the program will do", only superficially relevant. You think static analysis, type checking, intermediate representation, optimization, the translation of the program with exact semantics into another language, etc. - is 'superficially relevant' to understanding a program? > You can't solve the halting problem with compilers Now that's pretty irrelevant. > Also, did you catch the part where the point is about how expensive it is? Did you catch the part where I was only commenting on a specific part of the comment? But tell me, how expensive is it?