1. A computer-implemented method for implementing a synchronous reactive system in a graphical program, the method comprising: including a loop structure in the graphical program in response to first user input, wherein the loop structure is operable to execute iteratively in a synchronous manner, and wherein the loop structure is operable to store state information for a current iteration and to provide the state information for use in a next iteration of the loop; and including a plurality of graphical program nodes in the loop structure in response to second user input; wherein, during execution of the graphical program, for each iteration, the loop structure is operable to execute the plurality of graphical program nodes in the loop structure using stored state information from an immediately previous iteration, wherein the loop structure performs each iteration subject to a time constraint, and wherein the loop structure executes the plurality of graphical program nodes in a synchronous reactive manner.