Recursive Descent Parsing Overview
"Learn about recursive descent parsing, a top-down parsing technique that constructs parse trees starting from the top-level syntactic category. Explore examples and the approach of most top-down parsers. Discover a demonstration of a clite parser in Java."
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Presentation Transcript
Recursive Descent Parsing COMP 3200 Fall 2021 David J Stucki
ALERT Project #2 due November 1 (next Monday) Reading Assignment #8 Language Presentations!
Recursive Descent Parser An example of Top-Down Parsing Begins with the top level syntactic category (non-terminal start symbol), building the parse tree from the root Constructs the tree in a left-to-right pass through the Token stream, generating the tree as a pre-order traversal Tokens (terminals) are leaves Syntactic categories (non-terminals) are internal nodes
Recursive Descent Parser Most top-down parsers assume an LL approach Left-to-right scan of input Left-most derivation via grammar (what does this mean?) Example: clite if statement Concrete: <if> if ( <exp> ) <stmt> [ else <stmt> ] Abstract: Conditional = Expression test; Statement tPart, ePart
Recursive Descent Parser Concrete: <if> if ( <exp> ) <stmt> [ else <stmt> ] Abstract: Conditional = Expression test; Statement tPart, ePart if ( x == 0 ) Conditional test result = 1; tPart ePart else result = 2; Expression Statement Statement
Recursive Descent Parser Demo: clite parser in Java
