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Representation, Syntax, Paradigms, Types

Representation, Syntax, Paradigms, Types. Representation Formal Syntax Paradigms Data Types Type Inference. General Issues. Representation (of data, of computation) Form (Syntax) Meaning (Semantics) Paradigm (General way of thinking) Naming (names, name spaces, bindings, locality)

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Representation, Syntax, Paradigms, Types

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  1. Representation, Syntax, Paradigms, Types • Representation • Formal Syntax • Paradigms • Data Types • Type Inference CSE 341 -- S. Tanimoto Syntax and Types

  2. General Issues Representation (of data, of computation) Form (Syntax) Meaning (Semantics) Paradigm (General way of thinking) Naming (names, name spaces, bindings, locality) Functionality (numeric, data manip, I/O, communication, synchronization, security) Correctness (types, exception handling, error checking, bug avoidance) CSE 341 -- S. Tanimoto Syntax and Types

  3. Syntax Syntax: The grammatical form of programs. vs Semantics: The meaning of the program Syntax (of textual languages) is typically specified by production rules for a context-free grammar using Backus-Naur Form (BNF) or Extended BNF (EBNF) In visual languages, syntax is described by a set of restrictions on how diagrams may be constructed. (e.g., connection constraints) CSE 341 -- S. Tanimoto Syntax and Types

  4. Syntactic Components Identifiers and reserved words Numeric constants Parentheses, braces and brackets Expressions Statements CSE 341 -- S. Tanimoto Syntax and Types

  5. BNF (Backus-Naur Form) (2.0 * PI) / n <expression> ::= <expression> + <term> | <expression> - <term> | <term> <term> ::= <term> * <factor> | <term> / <factor> | <factor> <factor> ::= number | name | ( <expression> ) CSE 341 -- S. Tanimoto Syntax and Types

  6. Extended BNF Optional constructs written as [ x ] Zero or more of x written as { x } Choice (“or”) written using | Grouping with parentheses ( x | y ) as in { (x | y ) z } <expression> ::= <term> { (+ | -) <term> } <term> ::= <factor> { (* | /) <factor> } <factor> ::= ’(’ <expression> ’)’ | name | number CSE 341 -- S. Tanimoto Syntax and Types

  7. Derivation E ::= E + T | E - T | T T ::= T * F | T / F | F F ::= number | name | ( E ) E E + T T + T T / F + T F / F + T F / F + F 25 / F + F 25 / 100 + F 25 / 100 + total CSE 341 -- S. Tanimoto Syntax and Types

  8. Representation of Data Constants, Variables Types, classes Compounds: arrays, structures. Non-numeric objects: strings, images, audio. Values vs references Machine dependencies: word size, addressing resolution. In C, characters and booleans are actually integers. CSE 341 -- S. Tanimoto Syntax and Types

  9. Representation of Process Arithmetic and logical expressions Conditional expressions Loops Recursive and nonrecursive functions Multiple threads of control, forking, joining, synchronizing Single-threaded Parallel processing (in Single-instruction stream/multiple data stream processors) Throwing and catching of exceptions Declaration of constraints and rules CSE 341 -- S. Tanimoto Syntax and Types

  10. Paradigm General style of thinking that underlies a programming language Webster’s New World Dictionary: “a pattern, example, or model”. Imperative Rule-based Functional Logic Object-oriented Visual data-flow CSE 341 -- S. Tanimoto Syntax and Types

  11. The Imperative Paradigm An imperative program is a sequence of commands Read a value from a file. Evaluate an arithmetic expression. Assign a value to a variable. Test a condition and branch if it is true. Iterate a loop body until a condition is false. Print a value onto the screen. CSE 341 -- S. Tanimoto Syntax and Types

  12. The Functional Paradigm An functional program is a collection of function definitions and function applications. Define SQR(x): { Apply the * function to x and x} Apply SQR to 7; CSE 341 -- S. Tanimoto Syntax and Types

  13. The Object-Oriented Paradigm An object-oriented program is a collection of object class definitions, in which both data members and methods are specified. Class Student extends Person { int student_number; int get_student_number() { return student_number; } int set_student_number (int num) { student_number = num; } CSE 341 -- S. Tanimoto Syntax and Types

  14. The Rule-Based Paradigm A rule-based program is a collection of if-then rules. if name = "" then input name; if name starts with "A" then print "Early in the alphabet"; CSE 341 -- S. Tanimoto Syntax and Types

  15. The Logic-Programming Paradigm A logic program is a collection of logical propositions and questions. If x is a bird or an airplane, then x has wings. Tweety is a bird. Does Tweety have wings? CSE 341 -- S. Tanimoto Syntax and Types

  16. The Visual Data-Flow Paradigm A visual data-flow program is a diagram in which boxes represent operations and arrows indicate the flow of data from outputs of operations to inputs of other operations. 3x2 + 5x + 8 3 * * input x + * + 5 8 CSE 341 -- S. Tanimoto Syntax and Types

  17. Types Category or class for a value (or object) that permits its bits to be interpreted. Central Processing Unit instruction sets recognize certain types, such as integers and floats of different sizes. A programming language is not limited to the types that are directly supported by the CPU. CSE 341 -- S. Tanimoto Syntax and Types

  18. Strong vs Weak Typing Strong typing: (static and usually monomorphic) Every variable must have a type. A variable may receive only values of its type. Type-related bugs can be reduced. Type identification tags are not needed a run time. Weak typing: (dynamic and usually polymorphic) Variables need not be declared with particular types. The type of value held by a variable can change dynamically. Values must be tagged during execution with their types. CSE 341 -- S. Tanimoto Syntax and Types

  19. Coercion and Contagion Coercion: Any automatic type conversion. A value of type A is being assigned to a variable of type B. The value is coerced into one of type B. double x = 3 * 5; Contagion: Values of lower precision “catch” the precision of their higher precision co-arguments. int y = 10 * (3.1415 / 10); /* result is 3, not 0. */ In Common Lisp, when a rational meets a float, the rule of floating-point contagion rules. CSE 341 -- S. Tanimoto Syntax and Types

  20. Type Inference With weak typing, type inference is needed. (But ML, which is strongly typed, also uses a kind of type inference.) The resulting type can be determined from the types of the arguments, and the nature of the operations. Contagion provides one method for type inference: With strong typing, means for determining type equivalence are needed. int x[10]; int y[10]; Here x and y have structurally equivalent types. C and C++ recognize structurally equivalent types as equivalent. In Modula, most structurally equivalent types are not automatically considered equivalent, but they can be declared equivalent. CSE 341 -- S. Tanimoto Syntax and Types

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