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In computer programming, a callback is a function that is stored as data (a reference) and designed to be called by another function – often back to the original abstraction layer. A function that accepts a callback parameter may be designed to call back before returning to its caller which is known as synchronous or blocking .
If node A c-commands node B, and B also c-commands A, it can be said that A symmetrically c-commands B. If A c-commands B but B does not c-command A, then A asymmetrically c-commands B. The notion of asymmetric c-command plays a major role in Richard S. Kayne's theory of Antisymmetry.
Any function calling a CPS-ed function must either provide a new continuation or pass its own; any calls from a CPS-ed function to a non-CPS function will use implicit continuations. Thus, to ensure the total absence of a function stack, the entire program must be in CPS.
PostScript is an example of a postfix stack-based language. An expression example in this language is 2 3 mul ('mul' being the command for the multiplication operation). Calculating the expression involves understanding how stack orientation works. Stack orientation can be presented as the following conveyor belt analogy.
In C and C++, return exp; (where exp is an expression) is a statement that tells a function to return execution of the program to the calling function, and report the value of exp. If a function has the return type void , the return statement can be used without a value, in which case the program just breaks out of the current function and ...
This translates into "push four and five onto the stack, then, with the multiplication operator, pop two elements from the stack, multiply them and push the result onto the stack." Then the p command is used to examine (print out to the screen) the top element on the stack. The q command quits the invoked instance of dc. Note that numbers must ...
Calling f with a regular function argument first applies this function to the value 2, then returns 3. However, when f is passed to call/cc (as in the last line of the example), applying the parameter (the continuation) to 2 forces execution of the program to jump to the point where call/cc was called, and causes call/cc to return the value 2.
At function return, the stack pointer is instead restored to the frame pointer, the value of the stack pointer just before the function was called. Each stack frame contains a stack pointer to the top of the frame immediately below. The stack pointer is a mutable register shared between all invocations. A frame pointer of a given invocation of ...