1. Introduction

1.1. About this course

• Advanced subjects – for 3rd or 4th year students.

• Aim: Theoretical understanding of programming languages.

• Prerequisite: knowledge about two or more programming languages.

1.2. Evaluation

1.2.1. Allotment of points

• Weelky assignments: 20points

• Mid-term paper and presentation in class: 40points

• End-of-term exam: 40points

1.2.2. Distribution in the past years

• year 2021 — S:6, A:1, B:2, C:2, D:2

• year 2022 — S:13, A:16, B:5, C:3, D:13

1.3. A Fundamental Question

Why do we have so many programming languages?

• List of programming languages - Wikipedia

• New languages such as Go, Swift, and Rust has been developed recently.

• These languages are different from each other, but how different?

1.4. Definition of a language

When you want to define a new language, it is important that the definition is simple, rigorous and understandable.

• Scheme gives a mathematically precise definition which is hard to understand.

• BASIC and C had no rigid definitions at first. As a result, we had several slightly different language processors.

We need two things to define a language.

• syntax — how you write a program.

• semantics — what will happen when executiing a program

1.5. Differences in syntax

1.5.1. Character

• Unique symbols (cf. APL )

• Japanese characters (cf. Mind )

• Graphics instead of characters (cf. ToonTalk , Viscuit )

1.5.2. Grammar

There are languages called Esoteric progarmming language.

• Whitespace

• Befunge

1.6. Differences in semantics

Philosophically speaking, programming paradigm means “What is computation?”.

Imperative (Procedural)

Computation is a sequence of changing state.

Functional

Computation is a reduction of expression.

Logical

Computation is a proof of proposition.

1.7. Criteria for good programming languages

• Readablility and writability are not compatible in general.

• Efficiency

  • fast execution

  • fast compilation

  • fast development process

• Reliability

  • Strong typing, forcing execption handling, etc. (However, some people don’t like them)

• Other points

  • low learning cost

  • low development cost of language processors

  • abundant libraries

1.8. Reasons to study the theory of programming language

• You can select a language suitable for a task in your hand. — There is a saying ‘If all you have is a hammer, everything looks like a nail’.

• You can learn a new language easily. — You must continue to learn since progress of IT is very fast.

• It is an important base of the computer science.