diff --git a/src/com/annimon/ownlang/lib/NumberValue.java b/src/com/annimon/ownlang/lib/NumberValue.java
index c9d817e..91cf759 100644
--- a/src/com/annimon/ownlang/lib/NumberValue.java
+++ b/src/com/annimon/ownlang/lib/NumberValue.java
@@ -7,13 +7,14 @@ package com.annimon.ownlang.lib;
 public final class NumberValue implements Value {
     
     public static final NumberValue ZERO = new NumberValue(0);
+    public static final NumberValue ONE = new NumberValue(1);
+    
+    public static NumberValue fromBoolean(boolean b) {
+        return b ? ONE : ZERO;
+    }
     
     private final double value;
     
-    public NumberValue(boolean value) {
-        this.value = value ? 1 : 0;
-    }
-
     public NumberValue(double value) {
         this.value = value;
     }
diff --git a/src/com/annimon/ownlang/lib/Variables.java b/src/com/annimon/ownlang/lib/Variables.java
index 99a4c67..543fd37 100644
--- a/src/com/annimon/ownlang/lib/Variables.java
+++ b/src/com/annimon/ownlang/lib/Variables.java
@@ -1,8 +1,8 @@
 package com.annimon.ownlang.lib;
 
-import java.util.HashMap;
 import java.util.Map;
 import java.util.Stack;
+import java.util.concurrent.ConcurrentHashMap;
 
 /**
  *
@@ -15,15 +15,13 @@ public final class Variables {
     
     static {
         stack = new Stack<>();
-        variables = new HashMap<>();
-        variables.put("PI", new NumberValue(Math.PI));
-        variables.put("ПИ", new NumberValue(Math.PI));
-        variables.put("E", new NumberValue(Math.E));
-        variables.put("GOLDEN_RATIO", new NumberValue(1.618));
+        variables = new ConcurrentHashMap<>();
+        variables.put("true", NumberValue.ONE);
+        variables.put("false", NumberValue.ZERO);
     }
     
     public static void push() {
-        stack.push(new HashMap<>(variables));
+        stack.push(new ConcurrentHashMap<>(variables));
     }
     
     public static void pop() {
diff --git a/src/com/annimon/ownlang/lib/modules/std.java b/src/com/annimon/ownlang/lib/modules/std.java
index 24befd8..f274d02 100644
--- a/src/com/annimon/ownlang/lib/modules/std.java
+++ b/src/com/annimon/ownlang/lib/modules/std.java
@@ -70,6 +70,8 @@ public final class std implements Module {
 
         @Override
         public Value execute(Value... args) {
+            if (args.length == 0) return new NumberValue(RND.nextDouble());
+            
             int from = 0;
             int to = 100;
             if (args.length == 1) {
diff --git a/src/com/annimon/ownlang/parser/Parser.java b/src/com/annimon/ownlang/parser/Parser.java
index 3e45c6c..4d82169 100644
--- a/src/com/annimon/ownlang/parser/Parser.java
+++ b/src/com/annimon/ownlang/parser/Parser.java
@@ -122,11 +122,13 @@ public final class Parser {
     }
     
     private Statement forStatement() {
+        match(TokenType.LPAREN); // необязательные скобки
         final Statement initialization = assignmentStatement();
         consume(TokenType.COMMA);
         final Expression termination = expression();
         consume(TokenType.COMMA);
         final Statement increment = assignmentStatement();
+        match(TokenType.RPAREN);
         final Statement statement = statementOrBlock();
         return new ForStatement(initialization, termination, increment, statement);
     }
diff --git a/src/com/annimon/ownlang/parser/ast/BinaryExpression.java b/src/com/annimon/ownlang/parser/ast/BinaryExpression.java
index c71a217..6601197 100644
--- a/src/com/annimon/ownlang/parser/ast/BinaryExpression.java
+++ b/src/com/annimon/ownlang/parser/ast/BinaryExpression.java
@@ -98,6 +98,6 @@ public final class BinaryExpression implements Expression {
 
     @Override
     public String toString() {
-        return String.format("[%s %s %s]", expr1, operation, expr2);
+        return String.format("%s %s %s", expr1, operation, expr2);
     }
 }
diff --git a/src/com/annimon/ownlang/parser/ast/ConditionalExpression.java b/src/com/annimon/ownlang/parser/ast/ConditionalExpression.java
index d458bb2..c183806 100644
--- a/src/com/annimon/ownlang/parser/ast/ConditionalExpression.java
+++ b/src/com/annimon/ownlang/parser/ast/ConditionalExpression.java
@@ -45,6 +45,14 @@ public final class ConditionalExpression implements Expression {
     @Override
     public Value eval() {
         final Value value1 = expr1.eval();
+        switch (operation) {
+            case AND: return NumberValue.fromBoolean(
+                    (value1.asNumber() != 0) && (expr2.eval().asNumber() != 0) );
+            case OR: return NumberValue.fromBoolean(
+                    (value1.asNumber() != 0) || (expr2.eval().asNumber() != 0) );
+        }
+        
+        
         final Value value2 = expr2.eval();
         
         double number1, number2;
@@ -66,13 +74,10 @@ public final class ConditionalExpression implements Expression {
             case GT: result = number1 > number2; break;
             case GTEQ: result = number1 >= number2; break;
             
-            case AND: result = (number1 != 0) && (number2 != 0); break;
-            case OR: result = (number1 != 0) || (number2 != 0); break;
-            
             default:
                 throw new RuntimeException("Operation " + operation + " is not supported");
         }
-        return new NumberValue(result);
+        return NumberValue.fromBoolean(result);
     }
     
     @Override
@@ -82,6 +87,6 @@ public final class ConditionalExpression implements Expression {
 
     @Override
     public String toString() {
-        return String.format("[%s %s %s]", expr1, operation.getName(), expr2);
+        return String.format("%s %s %s", expr1, operation.getName(), expr2);
     }
 }
diff --git a/src/com/annimon/ownlang/parser/ast/FunctionDefineStatement.java b/src/com/annimon/ownlang/parser/ast/FunctionDefineStatement.java
index fe3016b..0980c11 100644
--- a/src/com/annimon/ownlang/parser/ast/FunctionDefineStatement.java
+++ b/src/com/annimon/ownlang/parser/ast/FunctionDefineStatement.java
@@ -32,6 +32,6 @@ public final class FunctionDefineStatement implements Statement {
 
     @Override
     public String toString() {
-        return "def (" + argNames.toString() + ") " + body.toString();
+        return String.format("def %s(%s) %s", name, argNames, body);
     }
 }
diff --git a/src/com/annimon/ownlang/parser/ast/VariableExpression.java b/src/com/annimon/ownlang/parser/ast/VariableExpression.java
index 3204ca0..1971eea 100644
--- a/src/com/annimon/ownlang/parser/ast/VariableExpression.java
+++ b/src/com/annimon/ownlang/parser/ast/VariableExpression.java
@@ -17,7 +17,7 @@ public final class VariableExpression implements Expression {
 
     @Override
     public Value eval() {
-        if (!Variables.isExists(name)) throw new RuntimeException("Variable does not exists");
+        if (!Variables.isExists(name)) throw new RuntimeException("Variable does not exists: " + name);
         return Variables.get(name);
     }