1. A method for automatic computer translation of input code including constraints to a computer executable imperative output program representation, the method comprising: providing one or more computer processors with an input source program, wherein the input source program is expressed in a programming language that provides for imperative specifications and also provides for declarative specification of constraints, and wherein the input source program includes one or more declaratively specified constraints in accordance with the programming language; translating, using the one or more computer processors, the input source program to the computer executable imperative output program representation, including: during compilation-time, automatically generating code comprising constraint representations based at least in part on the one or more declaratively specified constraints, including automatically generating code comprising one or more corresponding constraint reactor code objects to register input change notification upon instantiation, the one or more corresponding constraint reactor code objects being included in the computer executable imperative output program presentation and having imperative procedures that enforce the declaratively specified constraints; and for at least some of program data members of the input source program, automatically generating corresponding notification code to provide change notification and to accommodate registration for input change notification by constraint representations; and providing the computer executable imperative output program representation as an output.