ตัววัดในการเลือกข้อดีข้อเสียของโปรแกรมภาษา

ตัววัด
อ่านง่าย Readability
เขียนง่าย Writability
การทำงานตรวจสอบข้อผิดพลาด Reliability

Readability

"the most important criterium"
Factors:
Overall simplicity : พยายามทำอย่างไรก็ได้ให้ง่ายที่สุด

• Too many teatures is bad
• Multiplicity of features is bad e.g. increment an integer variable in c
• Operator overloading makes confusion

Orthogonality : ความสามารถในการกำหนดรูปแบบที่ยืดหยุ่น หรือการทำ Oveloading ได้

• Makes the language easy to learn and read
• Meaning is context independent
• e.g. pointer is able to point to any tpe of variable
• Lack of orthogonality leads to exceptions to the rules of the languages

Factors:
Control statements
Poor readable control structure(e.g. using goto satement)
Data type and structures
Presence of adequate facilities for defining data types and ad structures in a language
e.g. Boolean type as indicator flag
Record(instead of Arrays)
Class(Abstract Data Type)
Systax considerations

• Identifier forms(FORTRAN 77 allows six charaters at most)
• Special words(Ada uses and if to terminate a selection control and end loop to terminate a loop construct->greater readability)

Writability
Simplicity and orthogonality : ง่ายสามารถทำ Overloading ได้

• Misuse of some features static keyword in Java,c++
• Unknown features usage causes bizarre results
• Too much orthogonality may produce undetecte errors(any combination of primitive is legal) score = 14 /3 * 2;

Support for abstraction : รองรับการทำ Abstraction เช่นการซ่อนค่าต่าง ๆ โดยอ้างอิงรูปแบบของ Sub Program

• Ability to define and use complicated structures or poerations regardless the details
• e.g. using a sub program to implement a search,sort algorithm

Expressivity : การทำการเร็ว

• e.g. count++ in C(Shorter and more convenient)

Type Checking

• Earlier errors detection,less expensive repair
• Compile-time Checking is preferred

Exception handling

• The ability of a program to intercept run-time errors,take corrective measures,and then continue
• e.g. Ada,C++ and Java

Aliasing

• Having two or more distinct referencing methods,or names,for the same memory cell
• e.g. Using reference in Java,pointer in C++

Language Evaluation Criteria:Others
Cost
- Categories

• Programmer training(+simplicity+orthogonality+experience)
• Software creation(cost of writing program -> reduced in good IDE)
• Compilation(Fast)
• Execution(Fast)
• Compiler cost(For fee e.g. Java)
• Poor reliability(e.g. Critical system like nuclear power plant or X-ray machine if fail -> high cost of demange)
• Maintenance(corrections and modifications to add new capabilities)

Portability

• The ease of migrating from one implementation to another

Generality

• The applicability to a wide range of applications

Well-definedness

• The completeness and precision of a language's official defining document

Language Categories

1. Imperative

• Central features are variables,expression,assignment statement and iterative form of repetetive