1. Reasons to study concepts of PL
Increased capacity to express programming concepts
Improved background for choosing appropriate languages
Increased ability to learn new languages
Understanding the significance of implementation
Increased ability to design new languages
Overall advancement of computing

2. Programming Domains Scientific applications Business applications
Artificial intelligence
Systems programming
Scripting languages
Special purpose languages

3. Language Evaluation Criteria1.
2. Writability
- Factors: -
3. Reliability
Readability
Writability
Reliability
Cost
others

4. Readability The most important criteria Factors: Overall simplicity
Too many features is bad
Multiplicity of features is bad
Orthogonality
Control statements
Data type and structures
Syntax considerations

5. Orthogonality Makes the language easy to learn and read
Meaning is context independent
Small number of constructs for generating many structures.
int, float, double, arrays and pointers ==> ?
Few exceptions to rules: e.g. why can function return a struct, but not an array? Why are all parameters pass-by-value, except arrays?

6. Writability Simplicity and orthogonality Support for abstraction
No duplication
Avoid too much complexity; so many constructs, most users don’t know what to use
Support for abstraction
Subprograms, structures
Expressivity
for vs. while, ++ vs. + 1

7. Reliability Program should perform to specs under all conditions
Type checking of parameters, out-of-range errors
Exception handling
Aliasing
Generally bad, but can be useful for pass-by-reference
Readability and writability
Contorting the language to achieve an end can lead to errors.

8. Cost Programmer training Software creation Compilation speed
Execution speed
Compiler cost (Java vs. Pascal)
Poor reliability
Maintenance

9. Other Evaluation Criteria
Portability
Generality
Well-definedness

10. Influences on language design
Computer architecture
We use imperative languages, at least in part, because we use von Neumann machines
Programming methodologies
1950s and early 1960s: Simple applications; worry about machine efficiency
Late 1960s: People efficiency became important; readability, better control structures
Late 1970s: Data abstraction
Middle 1980s: Object-oriented programming
Early 1990s: Code re-use and libraries

11. Language Categories Imperative Functional Logic
Language Design Trade-offs 1.
Implementation Methods
Imperative
Functional
Logic
Object-oriented (closely related to imperative)
Mark-up languages (html) don’t describe computations, so don’t count

12. Language Design Tradeoffs
Reliability versus cost of execution
Writability versus readability
E.g: APL
Flexibility versus safety
E.g: PASCAL allows pointers and integers to be treated identically. Good for pointer calculations, but dangerous.

13. Implementation Methods
Compilation
Interpretation
Hybrid

14. Compiled languages Translate high-level program to machine code
Slow translation
Fast execution

15. Pure interpretation No translation Slow execution Becoming rare
Though, see Python and Java!

16. Hybrid implementation systems
Small translation cost
Medium execution speed

17. Programming Environments
The collection of tools used in software development
UNIX
An old operating system and tool collection
Borland C++
A PC environment for C and C++
Smalltalk & Lisp
A language processor/environment
Microsoft Visual C++
A large, complex visual environment

18. Chapter 1 2.