Tweaking to handle empty lines a bit better for #18.

api/src/main/java/io/github/applecommander/bastools/api/Parser.java

@@ -1,6 +1,7 @@
 package io.github.applecommander.bastools.api;
 
 import java.util.Objects;
+import java.util.Optional;
 import java.util.Queue;
 
 import io.github.applecommander.bastools.api.model.Line;
@@ -24,14 +25,14 @@ public class Parser {
 	public Program parse() {
 		Program program = new Program();
 		while (!tokens.isEmpty()) {
-			Line line = readLine(program);
-			program.lines.add(line);
+		    readLine(program).ifPresent(program.lines::add);
 		}
 		return program;
 	}
 	
-	public Line readLine(Program program) {
-		Line line = new Line(expectNumber(), program);
+	public Optional<Line> readLine(Program program) {
+	    return expectNumber().map(lineNumber -> {
+            Line line = new Line(lineNumber, program);
             while (!tokens.isEmpty() && tokens.peek().type != Type.EOL) {
                 Statement statement = readStatement();
                 if (statement != null) {
@@ -44,6 +45,7 @@ public class Parser {
                 tokens.remove();    // Skip that EOL
             }
             return line;
+	    });
 	}
 	
 	public Statement readStatement() {
@@ -57,15 +59,14 @@ public class Parser {
 		return statement;
 	}
 	
-	public int expectNumber() {
+	public Optional<Integer> expectNumber() {
 		Token c = tokens.remove();
 		while (c.type == Type.EOL) {
-			// Allow blank lines...
-			c = tokens.remove();
+		    return Optional.empty();
 		}
 		if (c.type != Type.NUMBER) {
 			throw new RuntimeException("Expected a number in line #" + c.line);
 		}
-		return c.number.intValue();
+		return Optional.of(c.number.intValue());
 	}
 }

api/src/test/java/io/github/applecommander/bastools/api/ParserTest.java

@@ -0,0 +1,25 @@
+package io.github.applecommander.bastools.api;
+
+import java.util.Queue;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import io.github.applecommander.bastools.api.model.Program;
+import io.github.applecommander.bastools.api.model.Token;
+import io.github.applecommander.bastools.api.utils.TokenBuilder;
+
+public class ParserTest {
+    @Test
+    public void testBlankLines() {
+        Queue<Token> tokens = TokenBuilder.builder()
+                .eol()  // Blank line before
+                .number(10.0).ident("A").syntax('=').number(42.0).eol()
+                .eol()  // Blank line after
+                .tokens();
+
+        Parser parser = new Parser(tokens);
+        Program program = parser.parse();
+        Assert.assertNotNull(program);
+    }
+}

api/src/test/java/io/github/applecommander/bastools/api/utils/TokenBuilder.java

@@ -0,0 +1,50 @@
+package io.github.applecommander.bastools.api.utils;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+import io.github.applecommander.bastools.api.model.ApplesoftKeyword;
+import io.github.applecommander.bastools.api.model.Token;
+
+public class TokenBuilder {
+    private int lineNumber;
+    private Queue<Token> tokens = new LinkedList<Token>();
+    
+    public static TokenBuilder builder() {
+        return new TokenBuilder();
+    }
+    
+    public TokenBuilder eol() {
+        add(Token.eol(lineNumber));
+        lineNumber += 1;
+        return this;
+    }
+    public TokenBuilder number(Double number) {
+        return add(Token.number(lineNumber, number));
+    }
+    public TokenBuilder ident(String text) {
+        return add(Token.ident(lineNumber, text));
+    }
+    public TokenBuilder comment(String text) {
+        return add(Token.comment(lineNumber, text));
+    }
+    public TokenBuilder string(String text) {
+        return add(Token.string(lineNumber, text));
+    }
+    public TokenBuilder keyword(ApplesoftKeyword keyword) {
+        return add(Token.keyword(lineNumber, keyword));
+    }
+    public TokenBuilder syntax(int ch) {
+        return add(Token.syntax(lineNumber, ch));
+    }
+    public TokenBuilder directive(String text) {
+        return add(Token.directive(lineNumber, text));
+    }
+    private TokenBuilder add(Token token) {
+        tokens.add(token);
+        return this;
+    }
+    public Queue<Token> tokens() {
+        return tokens;
+    }
+}