18. A system of one or more computers comprising: a processor; and a memory storing a plurality of instructions executable by the processor, the instructions including: an encoder module configured to map each module of program code of a plurality of modules of program code to one or more constraints, and generate mapped program code for each module of program code, the mapping based at least in part on a predetermined behavior for the module of program code that would be exhibited by the module when the module is executed; a solver module configured to determine whether one or more code constraints based on the mapped program code for a particular module are satisfiable by a constraint solver with one or more input-output constraints of a first specification comprising an input-output pair and identify one or more modules of program code that that have code constraints that are satisfiable with the input-output constraints; and a refiner module configured to incrementally refine the mapped program code.
18. A system of one or more computers comprising: a processor; and a memory storing a plurality of instructions executable by the processor, the instructions including: an encoder module configured to map each module of program code of a plurality of modules of program code to one or more constraints, and generate mapped program code for each module of program code, the mapping based at least in part on a predetermined behavior for the module of program code that would be exhibited by the module when the module is executed; a solver module configured to determine whether one or more code constraints based on the mapped program code for a particular module are satisfiable by a constraint solver with one or more input-output constraints of a first specification comprising an input-output pair and identify one or more modules of program code that that have code constraints that are satisfiable with the input-output constraints; and a refiner module configured to incrementally refine the mapped program code. 19. The electronic system of claim 18 , wherein the encoder module is configured to modify an indexing scheme used by the system for indexing the modules of program code, wherein the modified indexing scheme is based on the predetermined behavior for each module of program code.