1. In a graphical modeling environment, a method comprising: receiving a user request to define a parameter or a setting of a block in a simulatable block diagram model via a first graphical user interface; determining how defining the parameter or the setting of the block in the simulatable block diagram model according to the user request will alter code corresponding to the block, without generating entire code for the simulatable block diagram model, the entire code for the simulatable block diagram model being executable to simulate the simulatable block diagram model; automatically generating in real-time based on the determining, using a predictor mechanism, a preview of code representative of the code corresponding to the block prior to generating, using an execution engine, the entire code for the simulatable block diagram model, wherein: the preview of the code predicts and emulates the code corresponding to the block as if generated by the execution engine, the preview of the code and the code corresponding to the block are in a different coding format; and automatically displaying in real-time the preview of the code on a preview graphical user interface wherein the user can refine the preview of the code by altering the parameter or the setting for the block on the preview graphical user interface.