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Basic Compiler Functions Grammars Lexical Analysis Syntactic Analysis Code Generation

Basic Compiler Functions Grammars Lexical Analysis Syntactic Analysis Code Generation. High-Level Programming Language. A high-level programming language is described in terms of a grammar, which specifies the syntax of legal statements. An assignment statement:

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Basic Compiler Functions Grammars Lexical Analysis Syntactic Analysis Code Generation

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  1. Basic Compiler FunctionsGrammarsLexical AnalysisSyntactic AnalysisCode Generation

  2. High-Level Programming Language • A high-level programming language is described in terms of a grammar, which specifies the syntax of legal statements. • An assignment statement: • a variable name + an assignment operator + an expression

  3. Compiler • Compilation: matching statements (written by programmers) to structures (defined by the grammar) and generating the appropriate object code • Lexical analysis (scanning) • Scanning the source statement, recognizing and classifying the various tokens, including keywords, variable names, data types, operators, etc. • Syntactic analysis (parsing) • Recognizing each statement as some language construct described by the grammar • Semantics (code generation) • Generation of the object code

  4. Grammars • A grammar is a formal description of the syntax. • BNF (Backus-Naur Form): • A simple and widely used notations for writing grammars introduced by John Backus and Peter Naur in about 1960. • Meta-symbols of BNF: • ::= "is defined as" • | "or" • < > angle brackets used to surround non-terminal symbols • A BNF rule defining a nonterminal has the form: nonterminal ::= sequence_of_alternatives consisting of strings of terminals (tokens) or nonterminals separated by the meta-symbol |

  5. Simplified Pascal Grammar Recursive rule

  6. Parse Tree(Syntax Tree) READ(VALUE) VARIANCE:=SUMSQ DIV 100 – MEAN*MEAN The multiplication and division precede the addition and subtraction

  7. Parse Tree

  8. Parse Tree

  9. Lexical Analysis • Tokens might be defined by grammar rules to be recognized by the parser: • For better efficiency, a scanner can be used instead to recognize and output the tokens in a sequence represented by fixed-length codes and the associated token specifiers.

  10. Lexical Scan

  11. Modeling Scanners as Finite Automata • Tokens can often be recognized by a finite automaton, which consists of • A finite set of states (including a starting state and one or more final states) • A set of transtitions from one state to another

  12. Finite Automata for Typical Tokens

  13. Token Recognition Algorithm

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