CS 315
Homework Assignment 2

Closures and Referencing Environments in Dart, Golang, JavaScript, Lua, and Python

A closure is a subprogram and the referencing environment where it is defined. The referencing environment consists of all variables that are visible (in-scope) at the time the closure is created.

Closures are only needed when:

• Subprograms can be nested
• A subprogram can access nonlocal variables
• The subprogram can be called outside its defining scope

In this homework, you will investigate how closures and referencing environments are supported in the following programming languages: Dart, Golang, JavaScript, Lua, and Python.

In addition, you will investigate the following design issues related to closures:

1. Capture Semantics (Value vs. Reference-like behavior)
   Does the closure capture a snapshot of a variable, or does it reflect later changes to that variable? Illustrate how each language behaves.
2. The Loop Variable Trap
   When closures are created inside a loop, do they all share the same loop variable, or does each iteration create a new binding? Demonstrate the behavior and how (if necessary) it can be avoided.

You can use online compilers/interpreters.

For each language, prepare a single source code file that demonstrates the following tasks:

1. Define a nested subprogram
2. Access a nonlocal variable from the enclosing scope
3. Create and return a closure
4. Show that the closure preserves its referencing environment
5. Create multiple closures with different environments
6. Demonstrate how captured variables behave when their values change
7. Create closures inside a loop and analyze the loop variable behavior
8. Show that closures continue to work even after the outer subprogram is no longer directly accessible

Your example programs must be your own. Avoid plagiarism.

Part A - Closures in each language (45 points)

• Provide code
• Provide output
• Explain the behavior
• Explain how the language addresses the two design issues above

Part B - Evaluation (10 points)

• Readability
• Writability
• Clarity of closure semantics
• Behavior of captured variables (value vs. reference-like)
• Loop variable behavior

Part C - Learning strategy (10 points)

• Tools used
• Experiments performed
• Resources used

Part D - Sample Codes (35 points)

Submission:

A single zip or rar file should be submitted containing the following files with given names:

1. A single file for the Report, containing parts A, B, and C: ID_lastname_name_report.pdf (65 Points)
2. A folder called, Codes, for Part D. The contents of the folder will be as follows:
   1. A single file for Dart code: ID_lastname_name.dart (5 points)
   2. A single file for Go code:ID_lastname_name.go (5 points)
   3. A single file for JavaScript code: ID_lastname_name.html (5 points)
   4. A single file for Lua code: ID_lastname_name.lua (5 points)
   5. A single file for Python code: ID_lastname_name.py (5 points)

Please upload the zip or rar file you created to Moodle before the due date.

Important Notes:

• Late submissions will be accepted, with 20 points (out of 100) deduction for each extra day.
• You may use the tutorials available on the Internet as a reference, but do not derive your example from the contents of the tutorials. If you do so, your programs may be similar to others in the class, that causes a disciplinary investigation.
• Collaboration on the homework is not allowed.