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Programming Languages Fundamentals

Programming Languages Fundamentals. Cao Hoaøng Truï Khoa Coâng Ngheä Thoâng Tin Ñaïi Hoïc Baùch Khoa TP. HCM. Contents. Evolution and classification Formal syntax and semantics Compilation and interpretation. Machine Language. CPU. Memory. 0101001001101011. 1101111001001001. I/O.

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Programming Languages Fundamentals

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  1. Programming LanguagesFundamentals Cao Hoaøng Truï Khoa Coâng Ngheä Thoâng Tin Ñaïi Hoïc Baùch Khoa TP. HCM

  2. Contents • Evolution and classification • Formal syntax and semantics • Compilation and interpretation

  3. Machine Language CPU Memory 0101001001101011 1101111001001001 I/O 0001101010101010

  4. Machine Language Instruction: Operation Code Operands 10110011010010010011010110110001

  5. Assembly Language • A := B + C • if A = 0 then body • MOV r0, B ; move B into register r0 • ADD r0, C ; add • MOV A, r0 ; store • BNE L1 ; branch if result not equal 0 • body • L1:

  6. Language Levels Natural Language High-Level Low-Level Machine Language

  7. What Makes a Good Language? • Clarity, simplicity, unity of language concepts • Clarity of program syntax • Naturalness for the application • Support for abstraction • Ease of program verification

  8. What Makes a Good Language? • Programming environment • Portability of programs • Cost of use • program execution • program translation • program creation, testing, use • program maintenance

  9. Language Classification • Imperative • von Neumann Fortran, Pascal, Basic, C • object-oriented Smalltalk, Eiffel, C++, Java • Declarative • functional Lisp, ML, Haskell • dataflow Id, Val • logic Prolog, VisiCalc

  10. Von Neumann Languages • Most familiar and successful • Imperative statements • Modification of variables Fortran, Pascal, Basic, C, …

  11. Object-Oriented Languages • Imperative statements • Message passing among objects Smalltalk, Eiffel, C++, Java

  12. Functional Languages • Recursive definition of functions (lambda calculus) • Expressions of function composition Lisp, ML, Haskell

  13. Logic Languages • Logical facts and rules (predicate logic) • Computation as theorem proving Prolog, VisiCalc

  14. Dataflow Languages • Computation as token flow among nodes • Inherently parallel model Id, Val

  15. Contents • Evolution and classification • Formal syntax and semantics • Compilation and interpretation

  16. Formal Syntax and Semantics • Computer languages must be precise • Both their form (syntax) and meaning (semantics) must be specified without ambiguity • Both programmers and computers can tell what a program is supposed to do

  17. Formal Syntax • Abstract syntax • Context-free grammars • Backus-Naur formalism (BNF) • Syntax diagrams • Derivations and parse trees

  18. Abstract Syntax • Syntactic class • Syntactic form

  19. Example: Expressions • Syntactic class: E expression I identifier C constant O operator • Syntactic form: E = I | C | E O E | (E)

  20. Example: Expressions a * (2 + b) E O E

  21. Example: Expressions a - b - c E O E

  22. Abstract Syntax • Advantage: simple • Disadvantages: • No terminal symbols defined • Ambiguous

  23. Context-Free Grammars • Start symbol • Non-terminals • Terminals • Productions A  a1 | a2 | … | an (Noam Chomsky, 1959)

  24. Example: Unsigned Integers 6 2 5 7 3 <digit> <unsigned_integer>

  25. Example: Unsigned Integers • Start symbol <unsigned_integer> • Non-terminals <unsigned_integer>,<digit> • Terminals 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 • Productions <unsigned_integer>  <digit> | <digit> <unsigned_integer>

  26. Backus-Naur Formalism <unsigned_integer> ::= <digit> | <digit> <unsigned_integer> (John Backus, 1960)

  27. Example: Expressions <factor> 12 * 3 + 4 <term>

  28. Example: Expressions • Start symbol <expression> • Non-terminals <expression>, <term>, <factor>, <unsigned_integer>, <term_op>, <factor_op> • Terminals 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, +, -, *, /

  29. Example: Expressions • Productions: <expression>  <term> | <expression> <term_op> <term> <term>  <factor> | <term> <factor_op> <factor> <factor>  <unsigned_integer> | (<expression>) <term_op>  + | - <factor_op>  * | /

  30. Syntax Diagrams expression term expression term_op term

  31. Derivations <expression>  <expression> <term_op> <term>  <term> + <factor>  <term> <factor_op> <factor> + <unsigned_integer>  <factor>* <unsigned_integer> + 4  <unsigned_integer>* 3+ 4  12 * 3+ 4

  32. Parse Trees <expression> <expression> <term_op> <term> + <term> <factor> <term> <factor_op> <factor> <factor> * <unsigned_integer> <unsigned_integer> <unsigned_integer> 3 4 12

  33. Parse Trees <expression> <expression> <term_op> <term> + <term> <factor> <term> <factor_op> <factor> <factor> * <unsigned_integer> <unsigned_integer> <unsigned_integer> 3 4 12

  34. Formal Semantics • Operational semantics • Denotational semantics • Axiomatic semantics

  35. Operational Semantics • A virtual computer to execute a program. • A set of formally defined operations to specify how the internal state of the virtual computer may change.

  36. Denotational Semantics • Each program construct is a function that maps an input to an output. • A program is a composition of functions.

  37. Axiomatic Semantics • The effect of a statement is defined via its precondition and postcondition. • A set of axioms and rules to define the effect of program constructs.

  38. Axiomatic Semantics {P} S {Q} precondition statement postcondition

  39. Axiomatic Semantics • Axiom: {PxE} x := E {P}

  40. Axiomatic Semantics {x  2}x := x + 1{x  3} E = x + 1 P = x > 3 PxE= x + 1 > 3 = x > 2

  41. Axiomatic Semantics • Rule: if ({P} S1 {Q})  ({Q} S2 {R}) then {P} S1 ; S2 {R}

  42. Contents • Evolution and classification • Formal syntax and semantics • Compilation and interpretation

  43. Compilation and Interpretation Compiler Source program Target program Target program Input Output Interpreter Source program Output Input

  44. Compilation and Interpretation • Interpreter: better flexibility and diagnostics • Compiler: better performance

  45. Phases of Compilation Character stream Scanner (lexical analysis) Token stream Parser (syntactic analysis) Parse tree Semantic analysis Intermediate code Machine-independent code optimisation Optimised intermediate code Target code generation Target code Machine-specific code optimization Optimised target code

  46. Phases of Compilation c := a + b * 7 Scanner (lexical analysis) id1 := id2 + id3* 7 Parser (syntactic analysis)

  47. := + id1 * id2 id3 7 Phases of Compilation id1 := id2 + id3* 7 Parser (syntactic analysis)

  48. := id1 + id2 * id3 7 Phases of Compilation Semantic analysis CNV (7, , t1) * (id3, t1, t2) + (id2, t2, t3) ASS (t3, , id1)

  49. Phases of Compilation CNV (7, , t1) * (id3, t1, t2) + (id2, t2, t3) ASS (t3, , id1) Machine-independent code optimisation * (id3, 7.0, t1) + (id2, t1, id1)

  50. Phases of Compilation * (id3, 7.0, t1) + (id2, t1, id1) Target code generation MOV reg, id3 MUL reg, 7.0 ADD reg, id2 MOV id1, reg

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