CPSC 388 – Compiler Design and Construction Parsers – java cup

Java cup Parser Generator Java cup specification xxx.cup Java_cup.Main Parser Source code parser.java sym.java

Input to java_cup optional package and import declarations optional user code terminal and nonterminal declarations optional precedence and associativity declarations grammar rules with associated actions

Output from java_cup parser.java sym.java class parser { public parser(Yylex scanner) {…} public Symbol parse() {…} … } sym.java Class sym { public final static int TERMINAL=0; returns a Symbol whose value field contains the translation of the root nonterminal one public final static int for each terminal declared in the Java Cup specification.

Terminal and Non-Terminal Declarations /* terminals without values */ terminal name1, name2, ... ; /* terminals with values */ terminal type name1, name2, ... ; /* nonterminals */ non terminal type name1, name2, ... ; If you want to make use of the value associated with a terminal (the value field of the Symbol object returned by the scanner for that token) in your syntax-directed translation, then you must also declare the type of that value field. Similarly, you must declare the types of the translations associated with all of the nonterminals.

Precedence Declaration exp -> exp PLUS exp | exp MINUS exp | exp TIMES exp | exp EQUALS exp | ... This CFG is ambiguous, and will cause conflicts. Declare precedence and associativity in java_cup to fix ambiguity precedence left PLUS, MINUS; precedence left TIMES, DIVIDE; precedence nonassoc EQUALS;

Unary Minus Some tokens have multiple precedence: subtraction and unary minus Create a phony UMINUS terminal and declare its precedence Use UMINUS to change precedence in production rules: exp ::= MINUS exp {: RESULT = ... :} %prec UMINUS ;

Grammar Rules Declare start non-terminal (otherwise uses head of first production rule) start with program; Declare terminals and non-terminals: terminal SEMICOLON; terminal INT; terminal IdTokenVal ID; non terminal VarDeclNode varDecl; non terminal TypeNode type; non terminal IdNode id;

Grammar Rules Finally create production rules and actions: varDecl ::= type:t id:i SEMICOLON {: RESULT = new VarDeclNode(t, i); :} ; type ::= INT {: RESULT = new IntNode(); :} ; id ::= ID:i {: RESULT = new IdNode(i.idVal); :} ; ::= divides head from body of production rule :x used to give variable name to terminal/non terminals in body {: :} separate out the action (java code) RESULT special variable holding translation of head non-terminal ; each production rules ends with semicolon

java java_cup.Main < xxx.cup Running java_cup java java_cup.Main < xxx.cup

Programming Assignment #3 Download PROG3 skeleton under resources on Sakai