Cobbbbbbbnnnnnnnnnnnnnnnnncepts of PL.pptx
- 1. Programming Language Concepts Lecture 1- By Sadaf
- 2. What is a Programming Language ? A programming language is a set of rules that provides a way of telling a computer what operations to perform. A Programming language is a tool for developing executable models for a class of problem domains.
- 3. Syntax, Semantics and Pragmatics Syntax: Structure of Programs (tokens, keywords, statements) Semantics: What are meant by programs. Pragmatics:
- 4. Language Paradigms Imperative/ Procedural Languages Applicative/ Functional Languages Rule-based / Declarative Languages Object-Oriented Languages
- 5. Imperative/ Procedural Languages Statement Oriented languages that change machine state EX: (C, Pascal, FORTRAN, COBOL) Computation: a sequence of machine states(contents of memory) Syntax: S1, S2, S3,… where S1, S2,… are statements
- 6. Imperative/ Procedural Languages Imperative programs emphasize “tell what to do” They focus on evaluating expressions and storing results in a variable. The most common imperative language consists of statements such as : a=10; b= 5; c=a + b;
- 7. Applicative/ Functional Languages Programming consists of building the function that computes the answer EX: (ML, LISP) Computation: Function Composition is major operation Syntax: F1(F2(F3(X))) where F1, F2,F3 are functions and X is data.
- 8. Rule-Based / Declarative Languages Computation: Actions are specified by rules that check for the presence of certain enabling conditions. EX (Prolog) The order of execution is determined by the enabling conditions, not by the order of the statements. Syntax: Condition Action
- 9. Object-Oriented Languages Imperative languages that merge applicative design with imperative statements. Ex: (java, C++, Smalltalk) Syntax: set of objects (classes) containing data (imperative concepts) and methods (applicative concepts)
- 10. Different Types of Programming Domains Scientific applications Business applications Artificial intelligence Scripting languages Systems Programming
- 11. Programming Domains (Cont.’…) Scientific applications -Large number of floating point computations -Ex: Fortran Business applications -Produce reports, use decimal numbers and characters - Ex: COBOL
- 12. Programming Domains (Cont.’…) Artificial intelligence -Symbols rather than number manipulated -Ex: LISP Systems Programming -Need efficiency because of continuous use - Ex: C
- 13. Programming Domains (Cont.’…) Scripting Languages -Eclectic collection of languages : markup (e.g., XHTML), scripting (e.g., PHP), general-purpose (e.g., Java)
- 14. Criteria for Language Evaluation Readability :the ease with which programs can be read and understood Writeability :the ease with which a language can be used to create programs. Reliability :conformance to specifications (i.e., performs to its specifications) Cost : the ultimate total cost
- 15. Criteria for Language Evaluation (Cont..) Readability o Overall simplicity “Strongly affects readability” -Too many features make the language difficult to learn. Programmers tend to learn a subsets of the language and ignore its other features. Ex. ALGOL 60 - Multiplicity of features is also a complicating characteristics “having more than one way to accomplish a particular operation. Ex. Java
- 16. Criteria for Language Evaluation (Cont..) Readability o Orthogonality -Makes the language easy to learn and read. - Meaning is context independent. Pointers should be able to point to any type of variable or data structure.
- 17. Criteria for Language Evaluation (Cont..) Readability o Control Statements -It became widely recognized that indiscriminate use of goto statements severely reduced program readability. - Basic and Fortran in the early 70s lacked the control statements that allow strong restrictions on the use of gotos, so writing highly readable programs in those languages was difficult.
- 18. Criteria for Language Evaluation (Cont..) Readability o Control Statements -Since then, languages have included sufficient control structures. - The control statement design of a language is now a less important factor in readability that it was in the past.
- 19. Criteria for Language Evaluation (Cont..) Readability o Data Types and structures -The presence of adequate facilities for defining data types and structures in a language is another significant aid to reliability. - Ex: Boolean type. • timeout =1 or • timeout=true
- 20. Criteria for Language Evaluation (Cont..) Readability o Syntax Considerations -The syntax of the elements of a language has a significant effect on readability. -Identifier forms: Restricting identifiers to very short length detracts from readability. ANSI BASIC(1978) an identifier could consist only of a single letter followed by a single digit.
- 21. Criteria for Language Evaluation (Cont..) Writability -It is a measure of how easily a language can be used to create programs for a chosen problem domain - Most of the language characteristics that affect readability also affect writability.
- 22. Criteria for Language Evaluation (Cont..) Writability o Support for abstraction -The ability to define and use complex structures or operations in ways that allow details to be ignored. -
- 23. Criteria for Language Evaluation (Cont..) Writability o Simplicity and Orthogonality -A smaller number of primitive constructs and a consistent set of rules for combining them is much better than simply having a large number of primitives.
- 24. Criteria for Language Evaluation (Cont..) Reliability o Type checking -is simply testing for type errors in a given program, either by the compiler or during program execution. o Exception handling -the ability to intercepts run-time errors, take corrective measures, and then continue is a great aid to reliability.
- 25. Criteria for Language Evaluation (Cont..) Cost o Training programmers to use language. o Compiling Programs o Maintaining Programs o Language implementation system: availability of free compilers o Reliability: poor reliability leads to high costs.