fix the error handling in the Java binding

src/runtime/java/Test.java

@@ -6,7 +6,7 @@ public class Test {
 	public static void main(String[] args) {
 		PGF gr = null;
 		try {
-			gr = PGF.readPGF("/home/krasimir/www.grammaticalframework.org/treebanks/PennTreebank/ParseEngAbs.pgf");
+			gr = PGF.readPGF("Phrasebook.pgf");
 		} catch (FileNotFoundException e) {
 			e.printStackTrace();
 			return;
@@ -14,16 +14,22 @@ public class Test {
 			e.printStackTrace();
 			return;
 		}
-		
+
 		System.out.println(gr.getAbstractName());
 		for (Map.Entry<String,Concr> entry : gr.getLanguages().entrySet()) {
 			System.out.println(entry.getKey()+" "+entry.getValue()+" "+entry.getValue().getName());
 		}
-		
+
-		Concr eng = gr.getLanguages().get("ParseEng");
+		Concr eng = gr.getLanguages().get("PhrasebookEng");
-		for (ExprProb ep : eng.parse("Phr", "where are you")) {
+		Concr ger = gr.getLanguages().get("PhrasebookGer");
-			System.out.println("["+ep.getProb()+"] "+ep.getExpr());
+
-			System.out.println(eng.linearize(ep.getExpr()));
+		try {
+			for (ExprProb ep : eng.parse(gr.getStartCat(), "where is the conference")) {
+				System.out.println("["+ep.getProb()+"] "+ep.getExpr());
+				System.out.println(ger.linearize(ep.getExpr()));
+			}
+		} catch (ParseError e) {
+			System.out.println("Parsing failed at token \""+e.getToken()+"\"");
 		}
 	}
 }

src/runtime/java/jpgf.c

@@ -226,6 +226,7 @@ Java_org_grammaticalframework_pgf_Parser_parse
 
 		gu_pool_free(pool);
 		gu_pool_free(out_pool);
+		return NULL;
 	}
 
 	jclass expiter_class = (*env)->FindClass(env, "org/grammaticalframework/pgf/ExprIterator");

src/runtime/java/org/grammaticalframework/pgf/Concr.java

@@ -6,7 +6,7 @@ public class Concr {
 
 	public native String getName();
 
-	public Iterable<ExprProb> parse(String startCat, String s) {
+	public Iterable<ExprProb> parse(String startCat, String s) throws ParseError {
 		return new Parser(this, startCat, s);
 	}
 
@@ -25,7 +25,7 @@ public class Concr {
 	// private stuff
 	
 	private PGF gr;
-	public long ref;
+	private long ref;
 
 	private Concr(PGF gr, long ref) {
 		this.gr  = gr;

src/runtime/java/org/grammaticalframework/pgf/Expr.java

@@ -4,7 +4,7 @@ public class Expr {
 		private Pool pool;
 		private long ref;
 
-		private Expr(Pool pool, long ref) {
+		Expr(Pool pool, long ref) {
 			this.pool = pool;
 			this.ref  = ref;
 		}

src/runtime/java/org/grammaticalframework/pgf/ParseError.java

@@ -0,0 +1,11 @@
+package org.grammaticalframework.pgf;
+
+public class ParseError extends Exception {
+	public ParseError(String token) {
+		super(token);
+	}
+	
+	public String getToken() {
+		return getMessage();
+	}
+}

src/runtime/java/org/grammaticalframework/pgf/Parser.java

@@ -6,20 +6,30 @@ class Parser implements Iterable<ExprProb> {
 	private Concr concr;
 	private String s;
 	private String startCat;
+	private ExprIterator iter;
 
-	public Parser(Concr concr, String startCat, String s) {
+	public Parser(Concr concr, String startCat, String s) throws ParseError {
 		this.concr    = concr;
 		this.startCat = startCat;
 		this.s        = s;
+		this.iter     = parse(concr, startCat, s);
 	}
 
 	public Iterator<ExprProb> iterator() {
-		ExprIterator iter = parse(concr, startCat, s);
 		if (iter == null) {
-			throw new PGFError("The sentence cannot be parsed");
+			// If someone has asked for a second iterator over
+			// the same parse results then we have to parse again.
+			try {
+				return parse(concr, startCat, s);
+			} catch (ParseError e) {
+				return null;
+			}
+		} else {
+			ExprIterator tmp_iter = iter;
+			iter = null;
+			return tmp_iter;
 		}
-		return iter;
 	}
 
-	static native ExprIterator parse(Concr concr, String startCat, String s);
+	static native ExprIterator parse(Concr concr, String startCat, String s) throws ParseError;
 }