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17 Cards in this Set
- Front
- Back
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Syntax
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the form or structure of the expressions, statements, and program units
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Semantics
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the meaning of the expressions, statements, and program units
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sentence
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a string of characters over some alphabet
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language
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set of sentences
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lexeme
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lowest level syntactic unit of a language (e.g., *, sum, begin)
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token
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a category of lexemes (e.g., identifier)
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Recognizers
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reads input strings over the alphabet of the language and decides whether the input strings belong to the language
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Generators
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A device that generates sentences of a language
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Context-Free Grammars
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Language generators, meant to describe the syntax of natural languages. Developed by Noam Chomsky
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Backus-Naur Form
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Language generators, meant to describe the syntax of natural languages. Developed by Noam Chomsky
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Grammar
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a finite non-empty set of rules
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grammar is ambiguous if:
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it generates a sentential form that has two or more distinct parse trees
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Attribute Grammars
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a context-free grammar G = (S, N, T, P).
For each grammar symbol x there is a set A(x) of attribute values each rule has: -predicates to check for attribute consistency. -a set of functions that define certain attributes of the nonterminals in the rule. |
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needs for a methodology and notation for semantics:
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-Programmers need to know what statements mean
-Compiler writers must know exactly what language constructs do -Correctness proofs would be possible -Compiler generators would be possible -Designers could detect ambiguities and inconsistencies |
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Operational Semantics
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Describe the meaning of a program by executing its statements on a machine
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Evaluation of Denotational Semantics
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-Can be used to prove the correctness of programs
-Provides a rigorous way to think about programs -Can be an aid to language design -Has been used in compiler generation systems |
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Axiomatic Semantics
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Axioms or inference rules are defined for each statement type in the language (to allow transformations of logic expressions into more formal logic expressions)
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