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What is the role of a Syntax Analyser? 学び始める
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[1] read a sequence of tokens returned from the lexical analyser [2] group these tokens into phrases of certain phrase types according to the syntax of the programming language.
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What is the output of the Syntax Analysis phase 学び始める
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The output of this phase is an abstract syntax tree—a data structure that represents the syntactic structure of the source program.
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Given an input program, the goals of parsing is to? 学び始める
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[1] find all syntax errors and for each, produce an appropriate diagnostic message and recover quickly [2] produce the parse tree for the program for code generation.
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What are the 2 categories of parsers? 学び始める
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describe a top down parser 学び始める
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[1] Beginning with the root (the start symbol); [2] Each node is visited before its branches are followed; [3] Branch from a particular node are visited in left-to-right order - a leftmost derivation;
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Describe a bottom up parser 学び始める
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[1] Beginning at the leaves of parse tree (terminal symbols) and progressing toward the root. [2] Order is that of the reverse of a rightmost derivation
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Consider the following grammar: S → AB A → aA | ε B → b | bB What language does the grammar define? 学び始める
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The grammar defines strings consisting of any number (zero included) of a’s followed by at least one (and possibly more) b’s
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What is Recursive-Descent Parsers (RDP) 学び始める
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[1] A RDP consists of a collection of subprograms, many of which are recursive (therefore its name) and produces a parse tree in top-down order. [2] There is a subprogram for each nonterminal in the grammar.
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A nonterminal that has more than one RHS requires an initial process to determine which RHS it is to choose, give an example method to find The correct RHS 学び始める
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[1] The next token of input is compared with the first token that can be generated by each RHS until a match is found (e.g., the left parenthesis of the <factor> rule) [2] If no match is found, it is a syntax error.
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If a grammar has left recursion, either direct or indirect can it be used? 学び始める
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not directly as it leads to non-terminating recursion
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how can you transform left recursive grammar to one that is not? 学び始める
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For each nonterminal, A, Group the A-rules as A → Aα1 | ... | Aαm | β1 | β2 | ... | βn where none of the β’s begins with A Replace the original A-rules with A → β1A’ | β2A’ | ... | βnA’ A’ → α1A’ | α2A’ | ... | αmA’ | ε
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