JavaCC & JTB Aggelos Biboudis 1 

JavaCC • lexical analyzer (token manager) • generates a top-down parser (LL(k)) • a recursive descent parser • building trees with JJTree and JTB Aggelos Biboudis 2 

How to use • javacc Simple1.jj • javac *.java • java Simple1 Aggelos Biboudis 3 

JavaCC file • Options • PARSER_BEGIN(name) - PARSER_END(name) • Lexical specifications – SKIP, TOKEN, SPECIAL_TOKEN, MORE • List of productions – non terminal declaration followed by ; – declarations and statements within {} – lexical tokens as strings or regular expressions – use non terminals with [...] – actions Aggelos Biboudis 4 

Generated files • .java: The generate parser. • TokenManager.java: The generated token manager (or scanner/lexical analyzer). • Constants.java: A bunch of useful constants. • Also some boilerplate at "Token.java", "ParseException.java" Aggelos Biboudis 5 

Options • LOOKAHEAD • CHOICE_AMBIGUITY_CHEC K • OTHER_AMBIGUITY_CHECK • STATIC • SUPPORT_CLASS_VISIBILIT Y_PUBLIC • DEBUG_PARSER • DEBUG_LOOKAHEAD • DEBUG_TOKEN_MANAGER • ERROR_REPORTING • JAVA_UNICODE_ESCAPE • UNICODE_INPUT • IGNORE_CASE • USER_TOKEN_MANAGER • USER_CHAR_STREAM • BUILD_PARSER • BUILD_TOKEN_MANAGER • TOKEN_EXTENDS • TOKEN_FACTORY • TOKEN_MANAGER_USES_P ARSER • SANITY_CHECK • FORCE_LA_CHECK • COMMON_TOKEN_ACTION • CACHE_TOKENS • OUTPUT_DIRECTORY Aggelos Biboudis 6 

Productions • javacode_production – code instead EBNF when non context free production or difficult grammar in general – black box • bnf_production – local_lookahead – java_block – "(" expansion_choices ")" [ "+" | "*" | "?" ] – "[" expansion_choices "]" – [ java_assignment_lhs "=" ] regular_expression – [ java_assignment_lhs "=" ] java_identifier "(" java_expression_list ")" • regular_expr_production • token_manager_decls Aggelos Biboudis 7 

Regular Expressions in JavaCC • < ID: ["a"-"z","A"-"Z","_"] ( ["a"-"z","A"-"Z","_","0"-"9"] )* > • ( ... )+ • ( ... )? • ( r1 | r2 | ... ) • ["a"-"z"] • ~[] (any character) • ~["\n","\r"] (any character exception the new line characters) Aggelos Biboudis 8 

Choice conflict • No backtracking! – Decisions are based on local information Aggelos Biboudis 9 

Choice conflict (2) • Warning: Choice conflict involving two expansions at line 25, column 3 and line 31, column 3 respectively. A common prefix is: Consider using a lookahead of 2 for earlier expansion. Aggelos Biboudis 10 

Choice Conflict (3) • Turn it into LL(1) • Make use of LOOKAHEAD – Global lookahead via option (do not inc it without good reason!) – Local lookahead at choice point Aggelos Biboudis 11 

Other lookaheads • Syntactic lookahead • Semantic lookahead Aggelos Biboudis 12 

Java Tree Builder • Consumes a jj grammar file and generates – Syntax tree classes based on productions in grammar – Visitor design pattern – Visitor and GJVisitor interfaces – Two depth-first visitors: DepthFirstVisitor (simply for visiting) and GJDepthFirst (with generic return and args) – A JavaCC grammar (output jtb.out.jj. It builds the tree during parsing). Aggelos Biboudis 13 

Java Tree Builder Aggelos Biboudis 14 

How to use (from jtb example) • jtb subscheme.jj • Code a Visitor that is used in the jj (FreeVarFinderVisitor in the example) • javacc jtb.out.jj • javac SubScheme.java • java SubScheme < inputfile Aggelos Biboudis 15 

Tree Node Interface and Classes Aggelos Biboudis 16 • Based on the RHS of the production the public fields that are generated are of the following types – Node – NodeListInterface – NodeChoise – NodeList – NodeListOptional – NodeOptional – NodeSequence – NodeToken 

JavaCC vs SableCC • SableCC supports LALR(1) • JavaCC supports LL(1) • SableCC more OOP, JavaCC more imperative • Lookahead seems like a hack but it is more straightforward. Aggelos Biboudis 17 

Resources • http://javacc.java.net/doc/ • http://java.net/projects/javacc • http://www.engr.mun.ca/~theo/JavaC C-FAQ/javacc-faq-moz.htm • http://compilers.cs.ucla.edu/jtb/jtb- 2003/docs.html Aggelos Biboudis 18