Here is a brief overview of the source code:

src/
  Controller: This links the synthesis and the GUI together.
  Utils: Contains random utility methods.
  lang/: Defines and manipulates our target language.
    AST: Defines the AST classes.
    ASTUtils: Utilities for manipulating the AST.
    Memory: A class that represents the memory of a running program.
    Executor: Classes for executing programs.
    CachingExecutor: An executor that caches the results of expressions.
    Compiler: A (buggy) parser.
  gui/: The GUI.
    SynthesisGUI: Ties the GUI components together.
    Canvas: The main part of the GUI that displays and allows manipulation of the program.
    Shape: The shapes that are used on the canvas and utilities for manipulating them.
    Code: Pane that displays the code for the current trace.
    Controls: Toolbars and menubars.
  synthesis/: The synthesis.
    CodeGenerator: Generates expressions and statements given demonstrations.
    Synthesis: Contains most of the synthesis logic.
    SynthesisUtils: Contains utilities used in synthesis.
  test/: Unit tests and larger examples.
    Test: Code that tests synthesis.
    TestCompiler: Code that tests the parser.
    TestExecution: Code that tests executing programs.
    TestSynthesis: Code that tests synthesis.
    TestCommon: Utilities for testing.
    GuiTest: Contains some GUI test code as well as the selection sort algorithm.
    RBTree: Contains the Tree data structure and the insertion and rotation algorithms.
    Graph: Contains the Graph data structure and the DSW algorithm.