CMPT 489 / 980 Program Synthesis
Final Project
Phase I is due by 11:59pm PT on Wednesday Nov 8, 2023. Phase II is due by 11:59pm PT on Tuesday
Dec 5, 2023. Please submit them to Canvas on time. No late submission is accepted.
Requirements:
• This project must be your own work. No collaboration is permitted.
• The programming language of this project is Java 11.
• You can learn the code on slides and start from it.
• You can use third-party libraries but not existing synthesizers. However, you can implement the
algorithms in existing synthesizers by yourself.
1 Problem Description
Consider the following context-free grammar G
E ::= Ite(B, E, E) | Add(E, E) | Multiply(E, E) | x | y | z | 1 | 2 | 3
B ::= Lt(E, E) | Eq(E, E) | And(B, B) | Or(B, B) | Not(B)
x, y, z ∈ Variables 1, 2, 3 ∈ Constants
Here, E is the start symbol. E and B are non-terminals; all other symbols are terminals. The meaning
of terminal symbols are self-explanatory. Specifically, Ite is the if-then-else operator. Add is the addition
(+) operator. Multiply is the multiplication (∗) operator. x, y, z are integer variables. 1, 2, 3 are integer
constants. Lt is the less-than (<) operator. Eq is the equals (==) operator. And is the logical conjunction
(&&). Or is the logical disjunction (||). Not is the logical negation (!).
In this project, you need to write an example-based program synthesizer in Java. Specifically, the
synthesizer takes as input a list of input-output examples and the context-free grammar G and produces
as output an implementation of f(x, y, z) in the language of G such that f(x, y, z) is consistent with the
provided examples. You can assume f only uses three variables x, y, z, and all their types are Int. The return
type of f is also Int. If the synthesis succeeds, your program should print the program, e.g., Add(Add(y,
z), x), to the console. Otherwise, if the synthesis fails, the program should print null.
2 Codebase
A codebase is provided as the starting point. It contains the basic framework for the synthesizer. Details
are explained as follows.
Package synth.cfg
This package defines the data structure for the context-free grammar (CFG). It has the following classes
• Symbol. An abstract class for symbols in the CFG.
• Terminal. A subclass of Symbol that corresponds to terminals in the CFG.
• NonTerminal. A subclass of Symbol that corresponds to non-terminals in the CFG.
1
• Production. A class for productions in the CFG. A production is of the form
ReturnSymbol ::= Operator(ArgSymbol, ..., ArgSymbol)
• CFG. A class for representing the CFG. The most important method is getProductions, which takes
as input a non-terminal symbol N and returns as output a list of all productions with N being the
left-hand-side of the production.
Package synth.core
This package contains the classes for synthesizers, examples, programs, and interpreters.
• ASTNode. A class for general Abstract Syntax Tree (AST) nodes. The symbol fields corresponds to
the symbol in the CFG. The children field corresponds to the children nodes.
• Program. A class for representing a program. It only has one field root, which is the root node of the
corresponding AST.
• Example. A class that defines the data structure of an example. The input field is a map from variable
names to their values. The output field is the output value.
• Interpreter. A class that defines an interpreter of the language of G. The most important method
is the static method evaluate, which takes as input a program and an environment and returns as
output the evaluation result. The environment is essentially a map from variable names to their values,
just like the input field of Example. Concrete examples on how to use Interpreter.evaluate are
provided in the test class synth.core.InterpreterTests.
• ISynthesizer. An interface that defines the input and output of a synthesizer. The inputs are a CFG
and a list of examples. The output is a program.
• TopDownEnumSynthesizer. A top-down enumerative synthesizer that implements the ISynthesizer
interface. You need to implement this class.
Package synth.util
This package contains the utility classes and methods.
• FileUtils. A class for file operations. The readLinesFromFile static method reads a file into a list
of strings, where each line of the file is a string.
• Parser. A class for parsing the examples. The parseAnExample static method parses text of the form
“x=a, y=b, z=c -> d” to an object of class Example. The parseAllExamples static method parses
a list of examples from a list of strings, where each string corresponds to an example. It ignores empty
strings.
Class synth.Main
The main class of the framework. It has two methods.
• main. It is the entry of the program. It takes one command-line argument args[0] for the path to
the examples file.
• buildCFG. It builds the CFG G in Section 1.
Tests
JUnit tests are provided in the src/test directory. You are welcome to add more!
• synth.core.InterpreterTests. It contains several unit tests for the interpreter, which is also helpful
for understanding the usage of the interpreter.
2
Other Files
• pom.xml. The configuration file for Maven.
• examples.txt. A sample examples file.
3 Compilation and Execution
Compilation. This codebase uses the Maven build system. Suppose you enter the Synth directory, the
project can be easily compiled with one command
$ mvn package
Then you should be able to see the message “BUILD SUCCESS”. A directory called target will be created
and a jar file called synth-1.0.jar will be generated inside the target.
Execution. In the Synth directory, you can execute the program using the following command (use ;
instead of : in Windows)
$ java -cp lib:target/synth-1.0.jar synth.Main <path-to-examples-file>
where <path-to-examples-file> is the path to the examples file. For example, you can run
$ java -cp lib:target/synth-1.0.jar synth.Main examples.txt
You will see a runtime exception with message “To be implemented”, because the synthesizer is not implemented yet. After you finish implementing the synthesizer, you should see something like (not unique)
Add(Add(y, z), x)
4 Phase I
In Phase I, you need to implement a top-down enumerative synthesizer in synth.core.TopDownEnumSynthesizer.
Deliverable
A zip file called Phase1 Firstname Lastname.zip that contains at least the followings:
• The entire Synth directory. You can change existing code if you want, but please make sure the project
can be compiled and executed as explained in Section 3.
• A short report (1-2 pages) called Phase1 Firstname Lastname.pdf that explains the design choices,
features, tests, issues (if any), and anything else that you want to explain about your program.
5 Phase II
In Phase II, you can implement any synthesis algorithm that improves the performance of the synthesizer on
the same problem. You also need to create a small benchmark set and evaluate your algorithm
over the benchmarks.
A zip file called Phase2 Firstname Lastname.zip that contains at least the followings:
• The entire Synth directory. You can change existing code if you want, but please make sure the project
can be compiled and executed as explained in Section 3.
• A long report (5-6 pages) called Phase2 Firstname Lastname.pdf that explains the algorithms,
benchmarks, evaluation results, design choices, features, tests, issues (if any), and anything else
that you want to explain about your program.
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