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> It is a statement about what is "computable", which is the alpha and the omega of what computers can do. The Church-Turing thesis is about what functions are

> It is a statement about what is "computable", which is the alpha and the omega of what computers can do. The Church-Turing thesis is about what functions are computable. > A program that returns the system date operates on the machine state. You can treat this as "read from the tape" in the Turing sense or as input in the Lambda Calculus sense. Are you saying that the input tape may contain the later time at which a program will query the system's date? That seems like a physical impossibility to me. > If we imagine the world "as a computer" then it is natural to compute a later state of the world as a function of the previous state. The fundamental deficiency of this model is that it assumes you can put the entire world inside your program, and then get an entire new world as result. It utterly fails to take concurrency into consideration.

solidsnack9000 10y ago
> The Church-Turing thesis is about what functions are computable. Are you saying, that procedural programming can do something besides compute computable functions? > Are you saying that the input tape may contain the later time at which a program will query the system's date? That seems like a physical impossibility to me. When the computer retrieves the time from the clock, it does exactly that -- reads it from a location in memory. > > If we imagine the world "as a computer" then it is natural to compute a later state of the world as a function of the previous state. > The fundamental deficiency of this model is that it assumes you can put the entire world inside your program, and then get an entire new world as result. It utterly fails to take concurrency into consideration. How does it fail to take concurrency into account? We can treat the world as being made up of many objects and evolve their state simultaneously if we like.

solidsnack9000 10y ago

> The Church-Turing thesis is about what functions are computable. Are you saying, that procedural programming can do something besides compute computable functions? > Are you saying that the input tape may contain the later time at which a program will query the system's date? That seems like a physical impossibility to me. When the computer retrieves the time from the clock, it does exactly that -- reads it from a location in memory. > > If we imagine the world "as a computer" then it is natural to compute a later state of the world as a function of the previous state. > The fundamental deficiency of this model is that it assumes you can put the entire world inside your program, and then get an entire new world as result. It utterly fails to take concurrency into consideration. How does it fail to take concurrency into account? We can treat the world as being made up of many objects and evolve their state simultaneously if we like.