Added support for if/else to the expression parser. Basically same syntax as Java.

Also added a test case.

src/main/java/com/sk89q/worldedit/expression/parser/Parser.java

@@ -26,9 +26,11 @@
 
 import com.sk89q.worldedit.expression.Identifiable;
 import com.sk89q.worldedit.expression.lexer.tokens.IdentifierToken;
+import com.sk89q.worldedit.expression.lexer.tokens.KeywordToken;
 import com.sk89q.worldedit.expression.lexer.tokens.NumberToken;
 import com.sk89q.worldedit.expression.lexer.tokens.OperatorToken;
 import com.sk89q.worldedit.expression.lexer.tokens.Token;
+import com.sk89q.worldedit.expression.runtime.Conditional;
 import com.sk89q.worldedit.expression.runtime.Constant;
 import com.sk89q.worldedit.expression.runtime.Functions;
 import com.sk89q.worldedit.expression.runtime.RValue;
@@ -71,7 +73,7 @@ public static final RValue parse(List<Token> tokens, Map<String, RValue> variabl
     }
 
     private RValue parse() throws ParserException {
-        final RValue ret = parseMultipleStatements();
+        final RValue ret = parseStatements(false);
         if (position < tokens.size()) {
             final Token token = peek();
             throw new ParserException(token.getPosition(), "Extra token at the end of the input: " + token);
@@ -79,28 +81,76 @@ private RValue parse() throws ParserException {
         return ret;
     }
 
-    private RValue parseMultipleStatements() throws ParserException {
+    private RValue parseStatements(boolean singleStatement) throws ParserException {
         List<RValue> statements = new ArrayList<RValue>();
         loop: while (true) {
             if (position >= tokens.size()) {
                 break;
             }
 
-            switch (peek().id()) {
+            final Token current = peek();
+            switch (current.id()) {
             case ';':
                 ++position;
+
+                if (singleStatement) {
+                    break loop;
+                }
                 break;
 
             case '{':
                 statements.add(parseBlock());
+
+                if (singleStatement) {
+                    break loop;
+                }
                 break;
 
             case '}':
                 break loop;
 
+            case 'k':
+                final String keyword = ((KeywordToken) current).value;
+                switch (keyword.charAt(0)) {
+                case 'i': // if
+                    ++position;
+                    final RValue condition = parseBracket();
+                    final RValue truePart = parseStatements(true);
+                    final RValue falsePart;
+
+                    final Token next = peek();
+                    if ((next instanceof KeywordToken) && ((KeywordToken) next).value.equals("else")) {
+                        ++position;
+                        falsePart = parseStatements(true);
+                    } else {
+                        falsePart = null;
+                    }
+
+                    statements.add(new Conditional(current.getPosition(), condition, truePart, falsePart));
+                    break;
+
+                default:
+                    throw new ParserException(current.getPosition(), "Unimplemented keyword '" + keyword + "'");
+                }
+
+                if (singleStatement) {
+                    break loop;
+                }
+                break;
+
             default:
                 statements.add(parseExpression());
-                break;
+                
+                if (peek().id() == ';') {
+                    ++position;
+                    if (singleStatement) {
+                        break loop;
+                    }
+                    break;
+                }
+                else {
+                    break loop;
+                }
             }
         }
 
@@ -258,7 +308,7 @@ private final RValue parseBlock() throws ParserException {
             return new Sequence(peek().getPosition());
         }
 
-        final RValue ret = parseMultipleStatements();
+        final RValue ret = parseStatements(false);
 
         if (peek().id() != '}') {
             throw new ParserException(peek().getPosition(), "Unmatched opening brace");

src/main/java/com/sk89q/worldedit/expression/runtime/Conditional.java

@@ -0,0 +1,37 @@
+package com.sk89q.worldedit.expression.runtime;
+
+public class Conditional extends Node {
+    RValue condition;
+    RValue truePart;
+    RValue falsePart;
+
+    public Conditional(int position, RValue condition, RValue truePart, RValue falsePart) {
+        super(position);
+
+        this.condition = condition;
+        this.truePart = truePart;
+        this.falsePart = falsePart;
+    }
+
+    @Override
+    public double getValue() throws EvaluationException {
+        if (condition.getValue() > 0.0) {
+            return truePart.getValue();
+        }
+        else {
+            return falsePart == null ? 0 : falsePart.getValue();
+        }
+    }
+
+    @Override
+    public char id() {
+        return 't';
+    }
+
+    @Override
+    public String toString() {
+        return "if ("+condition+") { "+truePart+" } else { "+falsePart+" }";
+    }
+
+    //TODO: optimizer
+}

src/test/java/com/sk89q/worldedit/expression/ExpressionTest.java

@@ -10,7 +10,7 @@
 
 public class ExpressionTest {
     @Test
-    public void testEvaluate() throws Exception {
+    public void testEvaluate() throws ExpressionException {
         // check 
         assertEquals(1-2+3, simpleEval("1-2+3"), 0);
 
@@ -69,7 +69,25 @@ public void testAssign() throws ExpressionException {
         assertEquals(5, foo.getVariable("c").getValue(), 0);
     }
 
-    private double simpleEval(String expression) throws Exception {
+    @Test
+    public void testIf() throws ExpressionException {
+        assertEquals(40, simpleEval("if (1) x=4; else y=5; x*10+y;"), 0);
+        assertEquals(5, simpleEval("if (0) x=4; else y=5; x*10+y;"), 0);
+
+        // test 'dangling else'
+        final Expression expression1 = Expression.compile("if (1) if (0) x=4; else y=5;", "x", "y");
+        expression1.evaluate(1, 2);
+        assertEquals(1, expression1.getVariable("x").getValue(), 0);
+        assertEquals(5, expression1.getVariable("y").getValue(), 0);
+
+        // test if the if construct is correctly recognized as a statement
+        final Expression expression2 = Expression.compile("if (0) if (1) x=5; y=4;", "x", "y");
+        expression2.evaluate(1, 2);
+        assertEquals(4, expression2.getVariable("y").getValue(), 0);
+        
+    }
+
+    private double simpleEval(String expression) throws ExpressionException {
         return Expression.compile(expression).evaluate();
     }
 }