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24 Cards in this Set
- Front
- Back
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Syntax |
Form or structure of expression, statements and program units How programs in the language are built up |
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Semantics |
Meaning of expressions, statements, and program units What programs means |
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Sentence or statement |
String of characters over some alphabet |
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Language |
Set of sentences |
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Lexeme |
Lowest level of syntactic unit of language |
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Tokens |
Category of lexemes |
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Recognizers |
(Formal def of languages) Reads input strings over the alphabet and decides whether it belongs to the language (syntax analysis of compiler) |
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Generators |
(Formal def of languages) Generates sentences of a language, sentence is syntactically correct by comparison with structure of generator |
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Context-free Grammar |
(Formal methods in describing syntax) Noam Chomsky - mid 1950s Language generators - describe syntax of natural languages Class of languages - context-free languages |
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Backus-Naur Form |
John Backus - describe Algol 58 BNF - equiv to CFG |
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BNF fundamentals |
Uses abstraction LHS (abstraction or nonterminals) Nonterminals - enclosed in <> RHS - mixture of terminals (tokens and lexemes) and references to abstractions |
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Grammar (BNF) |
Collection of rules |
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Start symbol |
Special element of nonterminals |
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Rule or production |
LHS -> RHS |
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Syntatic list |
Described using recursion |
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When is rule recursive? |
Recursive if LHS appears in RHS |
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Derivation |
Repeated application of rules starting with start symbol and ending with a sentence |
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Sentential form |
Every string in derivation |
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Sentence |
Sentenial form that only has terminal symbols |
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Parse tree |
Hierarchal representation of a derivation |
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Ambiguous Grammar |
Grammar is ambiguous if it generates a sentential form that has two or more distinct parse trees |
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Operator associativity |
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Extended BNF |
Enhances readability and writability of BNF Optional [] Alternative (a|b) 0 or more repetitions {} |
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Other variations of EBNF |
Kleene Star * 0 or more Kleene Cross + 1 or more ? 0 or 1 () for grouping Alternative RHS - separate lines : instead of -> _opt for optional _oneof for choices |
