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primary data structure for next phases of compilaqon

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Unformatted text preview: r ID(party) Dan Grossman Dan Grossman Fall 2011 Fall 2011 We have: a scanner that generates a token stream SCOLON •  •  We want an abstract syntax tree (AST) –  A data structure that encodes the meaning of the program, and captures its structural features (loops, condiQonals, etc.) –  Primary data structure for next phases of compilaQon Winter 2013 UW CSE 401 (Michael Ringenburg) 6 How is this done? CSE341: Programming CSE341: Programming Languages Languages •  A grammar specifies the syntax of a language. Lecture 1 Lecture 1 •  Parsing aCourse Mechanics arse trees based on lgorithms bCourse Mechanics uild p a grammar Variabletream of tokens. ML Variable Bindings ML and a s Bindings –  Parse trees represent how a string can bDanerived e d Grossman from a grammar, and Fall encode meaning. 2011 •  –  E.g., add a and b, then add result to c. Expr à༎ Expr O Dan Grossmanp ID | ID F à༎ + Op all 2011 |- Can build AST by traversing parse tree (parsers may do this implicitly). Winter 2013 a+b+c Expr Expr ID(a) Expr Op ID(c) Op ID(b) + + UW CSE 401 (Michael Ringenburg) 7 DerivaQons vs. Parsing CSE341: Programming CSE341: Programming Languages Languages •  DerivaQon: a sequence of expansion steps, Lecture 1 Lecture 1 beginning with a start symbol and leading to a Course Course Mechanics Mechanics sequence of terminals Variable Bindings ML ML Variable Bindings •  Parsing: inverse of derivaQon Dan Grossman Dan Grossman –  Given a sequence of terminals (a.k.a. tokens) want Fall 2011 Fall 2011 to recover the nonterminals and structure (i.e., given string of terminals, find a derivaQon that generates them) •  Can represent derivaQon as a parse tree Winter 2013 UW CSE 401 (Michael Ringenburg) 8 Example DerivaQon C | program tatement CpSE341:statementSE341: sProgramming Languages rogram ::= Programming Languages G statement ::= assignStmt | ifStmt Lecture 1 assignStmt ::= id = expr ; ifStmt ::= if ( expr ) statement Course Mechanics expr ::= id | int | expr + expr id ::= a | b | c | i | j | k | n | x ML zVariable Bindings |y| int ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 Lecture...
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