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Chapter3: Language Translation issues

Chapter3: Language Translation issues. Programming language Syntax Key criteria concerning syntax Basic syntactic concepts Overall Program-Subprogram structure Stages in Translation Analysis of the source program Synthesis of the object program Bootstrapping. What is Syntax.

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Chapter3: Language Translation issues

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  1. Chapter3: Language Translation issues • Programming language Syntax • Key criteria concerning syntax • Basic syntactic concepts • Overall Program-Subprogram structure • Stages in Translation • Analysis of the source program • Synthesis of the object program • Bootstrapping

  2. What is Syntax The syntax of a programming language describes the structure of programs without any consideration of their meaning.

  3. Key criteria concerning syntax Readability – a program is considered readable if the algorithm and data are apparent by inspection. Writeability – ease of writing the program. Verifiability – ability to prove program correctness (very difficult issue) Translatability – ease of translating the program into executable form. Lack of ambiguity – the syntax should provide for ease of avoiding ambiguous structures

  4. Basic syntactic concepts • Character set – The alphabet of the language. Several different character sets are used: ASCII, EBCIDIC, Unicode • Identifiers – strings of letters of digits usually beginning with a letter • Operator Symbols – +-*/ • Keywords or Reserved Words – used as a fixed part of the syntax of a statement

  5. Basic syntactic concepts • Noise words – optional words inserted into statements to improve readability • Comments – used to improve readability and for documentation purposes. Comments are usually enclosed by special markers • Blanks – rules vary from language to language. Usually only significant in literal strings

  6. Basic syntactic concepts • Delimiters – used to denote the beginning and the end of syntactic constructs • Expressions – functions that access data objects in a program and return a value • Statements – these are the sentences of the language, they describe a task to be performed

  7. Overall Program-Subprogram Structure Separate subprogram definitions: Separate compilation, linked at load time E.G. C/C++ Separate data definitions:General approach in OOP. Nested subprogram definitions: Subprogram definitions appear as declarations within the main program or other subprograms. E.G. Pascal

  8. Overall Program-Subprogram Structure Separate interface definitions: C/C++ header files Data descriptions separated from executable statements. A centralized data division contains all data declarations. E.G. COBOL Unseparated subprogram definitions: No syntactic distinction between main program statements and subprogram statements. E.G BASIC

  9. Stages in Translation • Analysis of the source program • Synthesis of the object program • Bootstrapping

  10. Analysis of the source program • Lexical analysis (scanning) – identifying the tokens of the programming language: keywords, identifiers, constants and other symbols • In the program • void main() • { printf("Hello World\n"); } • the tokens are • void, main, (, ), {, printf, (, "Hello World\n", ), ;, }

  11. Syntactic and semantic analysis • Syntactic analysis (parsing) – determining the structure of the program, as defined by the language grammar. • Semantic analysis - assigning meaning to the syntactic structures • Example: int variable1; • meaning: 4 bytes for variable1 , a specific set of operations to be used with variable1.

  12. Basic semantic tasks • The semantic analysis builds the bridge between analysis and synthesis. • Basic semantic tasks: • Symbol–table maintenance • Insertion of implicit information • Error detection • Macro processing • Result : an internal representation, suitable to be used for code optimization and code generation.

  13. Synthesis of the object program Three main steps: Optimization - Removing redundant statements Code generation - generating assembler commands with relative memory addresses for the separate program modules - obtaining the object code of the program. Linking and loading - resolving the addresses - obtaining the executable code of the program.

  14. Optimization example Assembler code not optimized: LOAD_R B ADD_R C STORE_R Temp1 LOAD_R Temp1 ADD_R D STORE_R Temp2 LOAD_R Temp2 STORE_R A Intermediate code: Temp1 = B + C Temp2 = Temp1 + D A = Temp2 Statements in yellow can be removed

  15. Bootstrapping • The compiler for a given language can be written in the same language. • a program that translates some internal representation into assembler code • the programmer manually re-writes the compiler into the internal representation, using the algorithm that is encoded into the compiler. • From there on the internal representation is translated into assembler and then into machine language.

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