1. Lecture 2 Concepts of Programming Languages
Arne Kutzner
Hanyang University / Seoul Korea

2. Concepts of Programming Languages
Topics
Reasons for Studying Concepts of Programming Languages
Programming Domains
Language Evaluation Criteria
Influences on Language Design
Language Categories
Language Design Trade-Offs
Implementation Characteristics of Languages
Significance of individual languages in 2019
Concepts of Programming Languages

3. Reasons for Studying Concepts of Programming Languages
Improved background for choosing appropriate languages
Reduction of the risk of wrong decisions
Better use of languages that are already known
Better understanding of significance of language implementations
Concepts of Programming Languages

4. Concepts of Programming Languages
Programming Domains
Business applications
E.g. Middleware that implements some business process
Java, C++, C#, COBOL (still popular here!)
Web programming
Markup (HTML), Scripting (JavaScript (TypeScript), PHP etc.), general-purpose (e.g., Java),
General purpose applications like Photoshop, Autocad, Word etc.
Efficiency is important here
C++, C, Delphi
Systems programming / Operating System implementation
Low level, code efficiency is very important
C, Assembler
Scientific applications
E.g. Simulations; computational expensive tasks
Python, R, Fortran, (C, C++)
Artificial intelligence
C++, Python: Deep learning, TensorFlow, etc.
Older: Experimental work with languages like LISP (Scheme) and Prolog
Gaming, Embedded Systems, IoT …
Concepts of Programming Languages

5. Language Evaluation Criteria
Readability: Is this code easily readable?
Writability: Do you like this coding? [>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.> >>.<-.< >>+.>++.
Hello World in Brainfuck (
Reliability: unexpected crashes, blue screen of death
Cost: $, €, £ …
Concepts of Programming Languages

6. Evaluation Criteria: Readability / Writability
Overall readability/writability
Are the constructs of the language self describing/intuitive/well human readable …
Syntax considerations
Special symbols and their meaning (e.g. creation of compound statements)
Special words, meaningful keywords
Data types and structures
Adequate predefined data types and structures
The presence of adequate facilities for defining new data structures
Concepts of Programming Languages

7. Evaluation Criteria: Readability / Writability
Support for abstraction
The ability to define and use complex structures or operations in ways that allow details to be ignored
Expressivity
List comprehensions (Python, Haskell) etc.
Range-based for loops
Concepts of Programming Languages

8. Evaluation Criteria: Reliability
Static type checking vs. dynamic type checking
Recognition of type errors during compile time / runtime
Exception handling
Intercept run-time errors and take corrective measures
Concepts of Programming Languages

9. Evaluation Criteria: Cost
Training programmers to use the language
Language implementation system: Costs for compilers
Reliability: poor reliability leads to high costs
Maintenance costs
Deployment costs
Concepts of Programming Languages

10. Further Evaluation Criteria …
Portability
The ease with which programs can be moved from one implementation to another
Generality
The applicability to a wide range of applications
Well-definedness
The completeness and precision of the language’s official definition
Concepts of Programming Languages

11. Influences on Language Design
Computer Architecture
Architecture as driving factor of language design.
E.g. Von Neumann Architecture
OpenCL/CUDA for computing on GPUs
Programming Methodologies
Abstract data types
Concept of object orientation
Computational models / Mathematical models for computation
Lambda Calculus, Predicate Logic
Concepts of Programming Languages

12. Von Neumann Architecture
Concepts of Programming Languages

13. Programming Methodologies History / Mainstream developments
1950s and early 1960s: Simple applications; worry about machine efficiency
Late 1960s: People efficiency became more important; readability, better control structures
structured programming
top-down design and step-wise refinement
Late 1970s: Process-oriented to data-oriented
data abstraction
Middle 1980s: Object-oriented programming
Data abstraction + Inheritance + Polymorphism
Appearance of C++, Eiffel …
Concepts of Programming Languages

14. Concepts of Programming Languages
Imperative Languages
Characteristics:
Variables model memory cells
Assignment statements used for assigning values to memory cells
Iteration represents central concept
Inspired by von Neumann computers
Data and programs stored in memory
Memory is separate from CPU
Instructions and data are piped from memory to CPU
Concepts of Programming Languages

15. Language Categories / Families
Imperative / Object Oriented
Comprises languages that support object-oriented programming
Comprises scripting languages
Examples: C++, C, Java, C#, Python, JavaScript (TypeScript)
Markup and related
No logic, only pure descriptive: HTML, CSS, XML
Hybrids: PHP (Visualization plus logic), XSLT (XML plus logic)
Functional
Motivated by Lambda Calculus
Examples: LISP, Scheme, Haskell
Logic
Rule-based (rules are specified in no particular order)
Example: Prolog
Concepts of Programming Languages

16. Language Design Trade-Offs
Reliability vs. Cost of execution
Example: Java demands all references to array elements be checked for proper indexing, which leads to increased execution costs
Writability (flexibility) vs. Reliability
Example: C pointers are powerful and very flexible but they are unreliable
Concepts of Programming Languages

17. Implementation Characteristics of languages
Compilation
Programs are translated directly into machine language
Pure Interpretation
Programs are interpreted by an execution context known as an interpreter
Hybrids (Bytecode-based)
A compromise between compilers and pure interpreters
Concepts of Programming Languages

18. Concepts of Programming Languages
Compilation
Translate high-level program (source code) into machine code (executable file)
Phases of compilation process:
Lexical analysis: converts characters in the source program into lexical units
Syntax analysis: transforms lexical units into parse trees which represent the syntactic structure of program
Semantics analysis: generate intermediate code
Optimization: automatically apply improvements
Code generation: machine code is generated and written to "objects files"
Linking: collect "objects files" for creating an executable
Concepts of Programming Languages

19. Concepts of Programming Languages
Interpretation
Advantages:
No compilation involved
Boost portability!
Disadvantages:
Errors are recognized during runtime
No static type-check, because of the absence of compilation
Slow execution speed, if no clever just-in-time compilation is involved.
Significant in the area of Web programming: JavaScript, PHP
Concepts of Programming Languages

20. Bytecode-based Systems
A compromise between platform-specific compilation (e.g. C++) and pure interpretation
Program code is first translated to an intermediate code (called byte code) for later execution on a virtual machine
Much Faster than pure interpretation
Advantage: Portability
Examples
Java, C#
Concepts of Programming Languages

21. Bytecode-based Systems - Programming Workflow
Write Source Code
Source Code
program text in human readable form
all 5 steps of compilation
Compile Source Code
Byte Code
represents an intermediate code
using a byte-code interpreter
Execute Byte Code
Concepts of Programming Languages

22. Just-in-Time Compilation
Optimization for byte-code interpretation
Instead of interpreting the byte-code the byte-code is first compiled into machine code and this machine code is executed directly on processor level
Higher performance compared to pure interpretation
JIT-compilation requires initially extra time. So, it delays code execution / program start.
Concepts of Programming Languages

23. Concepts of Programming Languages
Preprocessors
A preprocessor processes/changes source code before it is compiled
Works like a macro mechanism and implements a text to text transformation
C, C++ preprocessor
expands #include, #define, and similar macros
Not popular outside C and C++
Main disadvantage: Compiler error messages can become quite cryptic/strange
Concepts of Programming Languages

24. Significance of individual languages in 2019
Java Programming