COS 333: Chapter 15, Part 1

Summary

The lecture introduces the shift in focus to chapters 15 and 16 on functional and logic programming languages, emphasizing their significance in exams due to heavy weighting. It delves into functional programming, highlighting its theoretical underpinnings with mathematical functions, the avoidance of side effects for referential transparency, and the pure functional approach eschewing variables. The discussion transitions to LISP and Scheme, exploring their history, basic constructs, and function applications, setting the stage for deeper exploration in subsequent lectures.

Takeaways

• 📚 The course is focusing on chapters 15 and 16 of the textbook, which cover functional programming languages and logic programming, as these are heavily emphasized in exams.
• 🔄 The professor has reordered the chapters to allow more time for practicals and lectures on the critical chapters, enhancing understanding and preparation for assessments.
• 🎯 Students are urged to concentrate on the material in chapters 15 and 16, as they carry significant weight in the grading for both semester tests and the final exam.
• 💻 Practical tasks, especially coding implementations similar to examples in chapters 15 and 16, are crucial for exam preparation and should be thoroughly practiced.
• 🔗 Chapter 15 references earlier chapters (5-8), and students are advised to consult both the textbook and the slides for a comprehensive understanding.
• 🚫 The entire Chapter 15 will not be covered; the focus will be on specific functional programming languages: Lisp and Scheme.
• 💡 Functional programming is based on mathematical functions, aiming to provide a more natural and theoretical approach to programming compared to imperative programming languages.
• 🔗 In functional programming, the concept of 'side effects' is generally discouraged as it introduces ambiguity and complexity in program execution.
• 🌐 Referential transparency, a property where equivalent expressions can be substituted without affecting program behavior, is a key advantage of functional programming languages.
• 🔑 Scheme, a dialect of Lisp, is emphasized for its simplicity and modernity, and is the primary focus for the course's functional programming section.
• 📝 Scheme uses a universal function 'eval' for interpreting expressions, demonstrating the power and flexibility inherent in functional programming languages.

Q & A

Why has the order of chapters in the textbook been changed for the lectures?

The order of chapters has been changed to allocate more lecture time and practical work to chapters 15 and 16, which are heavily emphasized in the semester tests and the exam.

What is the significance of focusing on chapters 15 and 16 in the course?

Chapters 15 and 16 cover functional programming languages and logic programming, which are important due to their significant weight in the exams and their practical applications.

What is the expectation for students regarding the practical tasks related to chapters 15 and 16?

Students are expected to complete all practicals related to these chapters, as the ability to implement code similar to examples given in these chapters may be required in exams.

How does the reference to earlier chapters in chapter 15 impact the preparation for the lectures?

Students should refer to both the textbook and the slides when preparing for chapter 15, as the slides provide additional information on topics from earlier chapters that are referenced.

Why are only certain topics within chapter 15 being covered in the lectures?

The lectures will focus only on Lisp and Scheme from chapter 15 because of their foundational importance in functional programming languages.

What is the fundamental concept behind functional programming languages?

Functional programming languages are based on mathematical functions, aiming to provide a more natural and mathematical way of expressing programs.

What is the primary concern for imperative programming languages?

The primary concern for imperative programming languages is efficiency, as they are designed to reflect the computing hardware they were made for.

What is a functional side effect and why are they generally considered bad?

A functional side effect is any change outside the scope of the function, such as modifying a parameter by reference or a global variable. They are considered bad because they lead to ambiguity in program execution.

What are the two approaches to solving the problem of ambiguity introduced by functional side effects?

The two approaches are disallowing functional side effects entirely, which increases language purity but reduces flexibility, and demanding a fixed operand evaluation order, which can limit compiler optimizations.

What is referential transparency and why is it important in programming?

Referential transparency means that equivalent expressions can be substituted for one another without affecting the program's behavior. It is important because it simplifies program semantics and eliminates ambiguity.

What is the difference between a pure functional programming language and an imperative one in terms of variable usage?

A pure functional programming language does not support variables at all, eliminating global variables and parameter modifications, whereas imperative programming languages rely heavily on variable management.

Why is the lack of support for variables in a pure functional programming language important?

The lack of support for variables ensures the elimination of functional side effects and state-associated functions, enforcing referential transparency and simplifying program semantics.

What are the two types of atoms in Lisp and how do they differ?

The two types of atoms in Lisp are symbols and numeric literals. Symbols are identifiers or names for concepts, while numeric literals are simply numeric values.

What is the significance of the list notation in Lisp and how is it used?

List notation in Lisp is used to represent both data structures and function applications. It allows for an ambiguous but powerful representation where the same list can be interpreted as data or a function call.

How does the lambda notation work in Lisp and what is its purpose?

Lambda notation in Lisp is used to define nameless functions. It specifies a set of parameters and an expression that defines what the function does, allowing for the creation of functions that can be used immediately where they are defined.

What is the relationship between Scheme and Lisp?

Scheme is a dialect of Lisp that was developed to be a cleaner, more modern, and simpler version of Lisp. It retains the same basic atoms and lists as Lisp but introduces other features and improvements.

How does the eval function work in Scheme and why is it significant?

The eval function in Scheme evaluates expressions. It is significant because it allows for the Scheme interpreter to be used as a function within the programming language, enabling powerful meta-programming capabilities.

What are the differences between the evaluation process for the define function and standard primitive functions in Scheme?

The define function in Scheme does not evaluate its first parameter as standard functions do. This is because the first parameter is typically a name that has not been bound yet, and evaluating it would result in an error.

Why are explicit input and output considered theoretical anomalies in pure functional programming languages?

Explicit input and output are considered anomalies in pure functional programming languages because input operations change the state of the program, and output operations can be seen as side effects, both of which contradict the stateless nature of pure functional programming.

How do arithmetic operations work in Scheme and what functions are provided for them?

In Scheme, all arithmetic operations are implemented as functions. The language specification provides a set of primitive arithmetic functions such as addition (+), subtraction (-), multiplication (*), division (/), and others like absolute value, square root, remainder, and min/max functions.

What is the purpose of the define function in Scheme and how does it differ from variable assignment in imperative languages?

The define function in Scheme is used to bind a name to a value or a lambda expression. It differs from variable assignment in imperative languages because once a name is bound to a value in Scheme, it cannot be rebound to a different value, making it more like a constant than a variable.

What are the built-in output functions provided by Scheme and how are they typically used?

Scheme provides built-in output functions like display, which prints the result of an evaluated expression, newline, which prints a new line character, and print, which allows formatted output. However, these functions are often not used directly, as the interpreter's normal behavior is to print the result of any top-level function application.