Added while loops to the expression parser.

Also added a test case.
Iterations are currently limited to 256 maximum.

src/main/java/com/sk89q/worldedit/expression/lexer/Lexer.java

@@ -107,7 +107,7 @@ public class Lexer {
         characterTokens.add(';');
     }
 
-    private static final Set<String> keywords = new HashSet<String>(Arrays.asList("if", "else"));
+    private static final Set<String> keywords = new HashSet<String>(Arrays.asList("if", "else", "while", "do"));
 
     private static final Pattern numberPattern = Pattern.compile("^([0-9]*(?:\\.[0-9]+)?(?:[eE][+-]?[0-9]+)?)");
     private static final Pattern identifierPattern = Pattern.compile("^([A-Za-z][0-9A-Za-z_]*)");

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

@@ -36,6 +36,7 @@ import com.sk89q.worldedit.expression.runtime.Functions;
 import com.sk89q.worldedit.expression.runtime.RValue;
 import com.sk89q.worldedit.expression.runtime.Sequence;
 import com.sk89q.worldedit.expression.runtime.Variable;
+import com.sk89q.worldedit.expression.runtime.While;
 
 /**
  * Processes a list of tokens into an executable tree.
@@ -112,7 +113,7 @@ public class Parser {
             case 'k':
                 final String keyword = ((KeywordToken) current).value;
                 switch (keyword.charAt(0)) {
-                case 'i': // if
+                case 'i': { // if
                     ++position;
                     final RValue condition = parseBracket();
                     final RValue truePart = parseStatements(true);
@@ -128,6 +129,31 @@ public class Parser {
 
                     statements.add(new Conditional(current.getPosition(), condition, truePart, falsePart));
                     break;
+                }
+
+                case 'w': { // while
+                    ++position;
+                    final RValue condition = parseBracket();
+                    final RValue body = parseStatements(true);
+
+                    statements.add(new While(current.getPosition(), condition, body, false));
+                    break;
+                }
+
+                case 'd': { // do
+                    ++position;
+                    final RValue body = parseStatements(true);
+
+                    final Token next = peek();
+                    if (!(next instanceof KeywordToken) || !((KeywordToken) next).value.equals("while")) {
+                        throw new ParserException(current.getPosition(), "Expected while");
+                    }
+                    ++position;
+                    final RValue condition = parseBracket();
+
+                    statements.add(new While(current.getPosition(), condition, body, true));
+                    break;
+                }
 
                 default:
                     throw new ParserException(current.getPosition(), "Unimplemented keyword '" + keyword + "'");

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

@@ -30,7 +30,11 @@ public class Conditional extends Node {
 
     @Override
     public String toString() {
-        return "if ("+condition+") { "+truePart+" } else { "+falsePart+" }";
+        if (falsePart == null) {
+            return "if ("+condition+") { "+truePart+" }";
+        } else {
+            return "if ("+condition+") { "+truePart+" } else { "+falsePart+" }";
+        }
     }
 
     //TODO: optimizer

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

@@ -0,0 +1,57 @@
+package com.sk89q.worldedit.expression.runtime;
+
+public class While extends Node {
+    RValue condition;
+    RValue body;
+    boolean footChecked;
+
+    public While(int position, RValue condition, RValue body, boolean footChecked) {
+        super(position);
+
+        this.condition = condition;
+        this.body = body;
+        this.footChecked = footChecked;
+    }
+
+    @Override
+    public double getValue() throws EvaluationException {
+        int iterations = 0;
+        double ret = 0.0;
+
+        if (footChecked) {
+            do {
+                ret = body.getValue();
+                ++iterations;
+                if (iterations > 256) {
+                    throw new EvaluationException(getPosition(), "Loop exceeded 256 iterations.");
+                }
+            } while (condition.getValue() > 0.0);
+        } else {
+            while (condition.getValue() > 0.0) {
+                ret = body.getValue();
+                ++iterations;
+                if (iterations > 256) {
+                    throw new EvaluationException(getPosition(), "Loop exceeded 256 iterations.");
+                }
+            }
+        }
+
+        return ret;
+    }
+
+    @Override
+    public char id() {
+        return 't';
+    }
+
+    @Override
+    public String toString() {
+        if (footChecked) {
+            return "do { "+body+" } while ("+condition+")";
+        } else {
+            return "while ("+condition+") { "+body+" }";
+        }
+    }
+
+    //TODO: optimizer
+}

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

@@ -84,7 +84,12 @@ public class ExpressionTest {
         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);
+    }
 
+    @Test
+    public void testWhile() throws ExpressionException {
+        assertEquals(5, simpleEval("c=5; a=0; while (c > 0) { ++a; --c; } a"), 0);
+        assertEquals(5, simpleEval("c=5; a=0; do { ++a; --c; } while (c > 0) a"), 0);
     }
 
     private double simpleEval(String expression) throws ExpressionException {