1. CPSC 388 – Compiler Design and Construction
Parsers – java cup

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

4. 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

5. 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.

6. 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.

7. 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;

8. 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 ;

9. 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;

10. 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

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

12. Programming Assignment #3
Download PROG3 skeleton under resources on Sakai