CS 330 Lecture 6 – Lexing, parsing, and translating
February 3, 2012 by Chris Johnson. Filed under
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cs330, lectures, spring 2012.
Agenda
- lexing
- recursive descent parsing
- writing interpreter glue
- adding state to ANTLR
- adding actions in ANTLR
Code
SLOWGO.g
grammar SLOWGO;
@members {
private int x = 0;
private int y = 0;
private int theta = 0;
private boolean isDrawing = false;
}
program
@init {
System.out.println("axis equal");
System.out.println("hold on");
}
: command+
;
command
: ROTATE NUMBER NEWLINE
{
theta = (theta + Integer.parseInt($NUMBER.text)) \% 360;
}
| FORWARD NUMBER NEWLINE
{
System.out.printf("plot([x1 x2], [y1 y2])\%n");
}
| DRAW state NEWLINE
{
}
;
state returns [boolean isOn]
: ON
{
isOn = true;
}
| OFF
{
isOn = false;
}
;
NUMBER
: '-'? ('0'..'9')+
;
ROTATE
: 'rotate'
;
FORWARD
: 'forward'
;
ON
: 'on'
;
OFF
: 'off'
;
DRAW
: 'draw'
;
WHITESPACE
: (' ' | '\t') {skip();}
;
NEWLINE
: '\r'? '\n'
;
SLOWGOInterpreter.java
import java.io.IOException;
import org.antlr.runtime.*;
public class SLOWGOInterpreter {
public static void main(String[] args) throws IOException, RecognitionException {
ANTLRInputStream in = new ANTLRInputStream(System.in);
SLOWGOLexer lexer = new SLOWGOLexer(in);
CommonTokenStream tokens = new CommonTokenStream(lexer);
SLOWGOParser parser = new SLOWGOParser(tokens);
parser.program();
}
}
Haiku