Introduced EvalError objects as possible values returned by expressions.

Extracted function and control name mappings to ControlFunctionRegistry.


git-svn-id: http://google-refine.googlecode.com/svn/trunk@148 7d457c2a-affb-35e4-300a-418c747d4874

src/main/java/com/metaweb/gridworks/commands/recon/ReconJudgeOneCellCommand.java

@@ -100,8 +100,8 @@ public class ReconJudgeOneCellCommand extends Command {
 
 		protected HistoryEntry createHistoryEntry() throws Exception {
 			Cell cell = _project.rows.get(rowIndex).getCell(cellIndex);
-            if (cell == null || ExpressionUtils.isBlank(cell.value)) {
+            if (cell == null || !ExpressionUtils.isNonBlankData(cell.value)) {
-				throw new Exception("Cell is blank");
+				throw new Exception("Cell is blank or error");
 			}
 			
 			Column column = _project.columnModel.getColumnByCellIndex(cellIndex);

src/main/java/com/metaweb/gridworks/commands/util/GetExpressionLanguageInfoCommand.java

@@ -12,8 +12,8 @@ import org.json.JSONWriter;
 
 import com.metaweb.gridworks.commands.Command;
 import com.metaweb.gridworks.expr.Control;
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
-import com.metaweb.gridworks.expr.Parser;
 
 public class GetExpressionLanguageInfoCommand extends Command {
 	
@@ -30,7 +30,7 @@ public class GetExpressionLanguageInfoCommand extends Command {
 			writer.key("functions");
 			writer.object();
 			{
-			    for (Entry<String, Function> entry : Parser.functionTable.entrySet()) {
+			    for (Entry<String, Function> entry : ControlFunctionRegistry.getFunctionMapping()) {
 			        writer.key(entry.getKey());
 			        entry.getValue().write(writer, options);
 			    }
@@ -40,7 +40,7 @@ public class GetExpressionLanguageInfoCommand extends Command {
             writer.key("controls");
             writer.object();
             {
-                for (Entry<String, Control> entry : Parser.controlTable.entrySet()) {
+                for (Entry<String, Control> entry : ControlFunctionRegistry.getControlMapping()) {
                     writer.key(entry.getKey());
 			        entry.getValue().write(writer, options);
                 }

src/main/java/com/metaweb/gridworks/commands/util/GuessTypesOfColumnCommand.java

@@ -86,7 +86,7 @@ public class GuessTypesOfColumnCommand extends Command {
 		
 		for (Row row : project.rows) {
 			Object value = row.getCellValue(cellIndex);
-			if (!ExpressionUtils.isBlank(value)) {
+			if (ExpressionUtils.isNonBlankData(value)) {
 				String s = value.toString().trim();
 				if (!sampleSet.contains(s)) {
 					samples.add(s);

src/main/java/com/metaweb/gridworks/commands/util/PreviewExpressionCommand.java

@@ -12,10 +12,12 @@ import org.json.JSONWriter;
 
 
 import com.metaweb.gridworks.commands.Command;
+import com.metaweb.gridworks.expr.EvalError;
 import com.metaweb.gridworks.expr.Evaluable;
 import com.metaweb.gridworks.expr.ExpressionUtils;
 import com.metaweb.gridworks.expr.HasFields;
 import com.metaweb.gridworks.expr.Parser;
+import com.metaweb.gridworks.expr.Parser.ParserException;
 import com.metaweb.gridworks.model.Cell;
 import com.metaweb.gridworks.model.Project;
 import com.metaweb.gridworks.model.Row;
@@ -69,15 +71,23 @@ public class PreviewExpressionCommand extends Command {
 					}
 					
 					if (result != null) {
-						if (result instanceof HasFields) {
+					    if (result instanceof EvalError) {
+                            result = "[Error: " + ((EvalError) result).message + "]";
+					    } else if (result instanceof HasFields) {
 							result = "[object " + result.getClass().getSimpleName() + "]";
 						}
 					}
 					writer.value(result);
 				}
 				writer.endArray();
+			} catch (ParserException e) {
+                writer.key("code"); writer.value("error");
+                writer.key("type"); writer.value("parser");
+                writer.key("message"); writer.value(e.getMessage());
 			} catch (Exception e) {
 				writer.key("code"); writer.value("error");
+                writer.key("type"); writer.value("other");
+                writer.key("message"); writer.value(e.getMessage());
 			}
 			
 			writer.endObject();

src/main/java/com/metaweb/gridworks/expr/Control.java

@@ -6,4 +6,6 @@ import com.metaweb.gridworks.Jsonizable;
 
 public interface Control extends Jsonizable {
 	public Object call(Properties bindings, Evaluable[] args);
+	
+	public String checkArguments(Evaluable[] args);
 }

src/main/java/com/metaweb/gridworks/expr/ControlFunctionRegistry.java

@@ -0,0 +1,128 @@
+package com.metaweb.gridworks.expr;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+import java.util.Map.Entry;
+
+import com.metaweb.gridworks.expr.controls.ForEach;
+import com.metaweb.gridworks.expr.controls.ForNonBlank;
+import com.metaweb.gridworks.expr.controls.If;
+import com.metaweb.gridworks.expr.controls.With;
+import com.metaweb.gridworks.expr.functions.And;
+import com.metaweb.gridworks.expr.functions.Ceil;
+import com.metaweb.gridworks.expr.functions.EndsWith;
+import com.metaweb.gridworks.expr.functions.Floor;
+import com.metaweb.gridworks.expr.functions.Get;
+import com.metaweb.gridworks.expr.functions.IndexOf;
+import com.metaweb.gridworks.expr.functions.IsBlank;
+import com.metaweb.gridworks.expr.functions.IsNotBlank;
+import com.metaweb.gridworks.expr.functions.IsNotNull;
+import com.metaweb.gridworks.expr.functions.IsNull;
+import com.metaweb.gridworks.expr.functions.Join;
+import com.metaweb.gridworks.expr.functions.LastIndexOf;
+import com.metaweb.gridworks.expr.functions.Length;
+import com.metaweb.gridworks.expr.functions.Ln;
+import com.metaweb.gridworks.expr.functions.Log;
+import com.metaweb.gridworks.expr.functions.Max;
+import com.metaweb.gridworks.expr.functions.Min;
+import com.metaweb.gridworks.expr.functions.Mod;
+import com.metaweb.gridworks.expr.functions.Not;
+import com.metaweb.gridworks.expr.functions.Or;
+import com.metaweb.gridworks.expr.functions.Replace;
+import com.metaweb.gridworks.expr.functions.Reverse;
+import com.metaweb.gridworks.expr.functions.Round;
+import com.metaweb.gridworks.expr.functions.Slice;
+import com.metaweb.gridworks.expr.functions.Sort;
+import com.metaweb.gridworks.expr.functions.Split;
+import com.metaweb.gridworks.expr.functions.StartsWith;
+import com.metaweb.gridworks.expr.functions.ToLowercase;
+import com.metaweb.gridworks.expr.functions.ToNumber;
+import com.metaweb.gridworks.expr.functions.ToString;
+import com.metaweb.gridworks.expr.functions.ToTitlecase;
+import com.metaweb.gridworks.expr.functions.ToUppercase;
+
+public class ControlFunctionRegistry {
+
+    static private Map<String, Function> s_nameToFunction = new HashMap<String, Function>();
+    static private Map<Function, String> s_functionToName = new HashMap<Function, String>();
+    
+    static private Map<String, Control> s_nameToControl = new HashMap<String, Control>();
+    static private Map<Control, String> s_controlToName = new HashMap<Control, String>();
+    
+    static public Function getFunction(String name) {
+        return s_nameToFunction.get(name);
+    }
+    static public String getFunctionName(Function f) {
+        return s_functionToName.get(f);
+    }
+    static public Set<Entry<String, Function>> getFunctionMapping() {
+        return s_nameToFunction.entrySet();
+    }
+
+    static public Control getControl(String name) {
+        return s_nameToControl.get(name);
+    }
+    static public String getControlName(Function f) {
+        return s_controlToName.get(f);
+    }
+    static public Set<Entry<String, Control>> getControlMapping() {
+        return s_nameToControl.entrySet();
+    }
+
+    static protected void registerFunction(String name, Function f) {
+        s_nameToFunction.put(name, f);
+        s_functionToName.put(f, name);
+    }
+
+    static protected void registerControl(String name, Control c) {
+        s_nameToControl.put(name, c);
+        s_controlToName.put(c, name);
+    }
+
+    static {
+        registerFunction("toString", new ToString());
+        registerFunction("toNumber", new ToNumber());
+        
+        registerFunction("toUppercase", new ToUppercase());
+        registerFunction("toLowercase", new ToLowercase());
+        registerFunction("toTitlecase", new ToTitlecase());
+        
+        registerFunction("get", new Get());
+        registerFunction("slice", new Slice());
+        registerFunction("substring", new Slice());
+        registerFunction("replace", new Replace());
+        registerFunction("split", new Split());
+        registerFunction("length", new Length());
+        
+        registerFunction("indexOf", new IndexOf());
+        registerFunction("lastIndexOf", new LastIndexOf());
+        registerFunction("startsWith", new StartsWith());
+        registerFunction("endsWith", new EndsWith());
+        registerFunction("join", new Join());
+        registerFunction("reverse", new Reverse());
+        registerFunction("sort", new Sort());
+        
+        registerFunction("round", new Round());
+        registerFunction("floor", new Floor());
+        registerFunction("ceil", new Ceil());
+        registerFunction("mod", new Mod());
+        registerFunction("max", new Max());
+        registerFunction("min", new Min());
+        registerFunction("log", new Log());
+        registerFunction("ln", new Ln());
+        
+        registerFunction("and", new And());
+        registerFunction("or", new Or());
+        registerFunction("not", new Not());
+        registerFunction("isNull", new IsNull());
+        registerFunction("isNotNull", new IsNotNull());
+        registerFunction("isBlank", new IsBlank());
+        registerFunction("isNotBlank", new IsNotBlank());
+
+        registerControl("if", new If());
+        registerControl("with", new With());
+        registerControl("forEach", new ForEach());
+        registerControl("forNonBlank", new ForNonBlank());
+    }
+}

src/main/java/com/metaweb/gridworks/expr/EvalError.java

@@ -0,0 +1,26 @@
+package com.metaweb.gridworks.expr;
+
+import java.util.Properties;
+
+import org.json.JSONException;
+import org.json.JSONWriter;
+
+import com.metaweb.gridworks.Jsonizable;
+
+public class EvalError implements Jsonizable {
+    final public String message;
+    
+    public EvalError(String message) {
+        this.message = message;
+    }
+    
+    public void write(JSONWriter writer, Properties options)
+            throws JSONException {
+        
+        writer.object();
+        writer.key("type"); writer.value("error");
+        writer.key("message"); writer.value(message);
+        writer.endObject();
+    }
+
+}

src/main/java/com/metaweb/gridworks/expr/ExpressionUtils.java

@@ -32,9 +32,20 @@ public class ExpressionUtils {
         }
     }
     
+    static public boolean isError(Object o) {
+        return o != null && o instanceof EvalError;
+    }
+    /*
     static public boolean isBlank(Object o) {
         return o == null || (o instanceof String && ((String) o).length() == 0);
     }
+    */
+    static public boolean isNonBlankData(Object o) {
+        return 
+            o != null && 
+            !(o instanceof EvalError) &&
+            (!(o instanceof String) || ((String) o).length() > 0);
+    }
 
     static public boolean isTrue(Object o) {
         return o != null && 

src/main/java/com/metaweb/gridworks/expr/FieldAccessorExpr.java

@@ -13,10 +13,15 @@ public class FieldAccessorExpr implements Evaluable {
 	
 	public Object evaluate(Properties bindings) {
 		Object o = _inner.evaluate(bindings);
-		if (o != null && o instanceof HasFields) {
+		if (ExpressionUtils.isError(o)) {
+		    return o;
+		} else if (o == null) {
+		    return new EvalError("Cannot retrieve field from null");
+		} else if (o instanceof HasFields) {
 			return ((HasFields) o).getField(_fieldName, bindings);
+		} else {
+		    return new EvalError("Object does not have any field, including " + _fieldName);
 		}
-		return null;
 	}
 
 	@Override

src/main/java/com/metaweb/gridworks/expr/FunctionCallExpr.java

@@ -14,7 +14,11 @@ public class FunctionCallExpr implements Evaluable {
 	public Object evaluate(Properties bindings) {
 		Object[] args = new Object[_args.length];
 		for (int i = 0; i < _args.length; i++) {
-			args[i] = _args[i].evaluate(bindings);
+		    Object v = _args[i].evaluate(bindings);
+		    if (ExpressionUtils.isError(v)) {
+		        return v;
+		    }
+ 			args[i] = v;
 		}
 		return _function.call(bindings, args);
 	}

src/main/java/com/metaweb/gridworks/expr/OperatorCallExpr.java

@@ -14,7 +14,11 @@ public class OperatorCallExpr implements Evaluable {
 	public Object evaluate(Properties bindings) {
 		Object[] args = new Object[_args.length];
 		for (int i = 0; i < _args.length; i++) {
-			args[i] = _args[i].evaluate(bindings);
+			Object v = _args[i].evaluate(bindings);
+            if (ExpressionUtils.isError(v)) {
+                return v;
+            }
+            args[i] = v;
 		}
 		
 		if (args.length == 2) {

src/main/java/com/metaweb/gridworks/expr/Parser.java

@@ -1,109 +1,30 @@
 package com.metaweb.gridworks.expr;
 
-import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
-import java.util.Map;
 
 import com.metaweb.gridworks.expr.Scanner.NumberToken;
 import com.metaweb.gridworks.expr.Scanner.Token;
 import com.metaweb.gridworks.expr.Scanner.TokenType;
-import com.metaweb.gridworks.expr.controls.ForEach;
-import com.metaweb.gridworks.expr.controls.ForNonBlank;
-import com.metaweb.gridworks.expr.controls.If;
-import com.metaweb.gridworks.expr.controls.With;
-import com.metaweb.gridworks.expr.functions.And;
-import com.metaweb.gridworks.expr.functions.Ceil;
-import com.metaweb.gridworks.expr.functions.EndsWith;
-import com.metaweb.gridworks.expr.functions.Floor;
-import com.metaweb.gridworks.expr.functions.Get;
-import com.metaweb.gridworks.expr.functions.IndexOf;
-import com.metaweb.gridworks.expr.functions.IsBlank;
-import com.metaweb.gridworks.expr.functions.IsNotBlank;
-import com.metaweb.gridworks.expr.functions.IsNotNull;
-import com.metaweb.gridworks.expr.functions.IsNull;
-import com.metaweb.gridworks.expr.functions.Join;
-import com.metaweb.gridworks.expr.functions.LastIndexOf;
-import com.metaweb.gridworks.expr.functions.Length;
-import com.metaweb.gridworks.expr.functions.Ln;
-import com.metaweb.gridworks.expr.functions.Log;
-import com.metaweb.gridworks.expr.functions.Max;
-import com.metaweb.gridworks.expr.functions.Min;
-import com.metaweb.gridworks.expr.functions.Mod;
-import com.metaweb.gridworks.expr.functions.Not;
-import com.metaweb.gridworks.expr.functions.Or;
-import com.metaweb.gridworks.expr.functions.Replace;
-import com.metaweb.gridworks.expr.functions.Reverse;
-import com.metaweb.gridworks.expr.functions.Round;
-import com.metaweb.gridworks.expr.functions.Slice;
-import com.metaweb.gridworks.expr.functions.Sort;
-import com.metaweb.gridworks.expr.functions.Split;
-import com.metaweb.gridworks.expr.functions.StartsWith;
-import com.metaweb.gridworks.expr.functions.ToLowercase;
-import com.metaweb.gridworks.expr.functions.ToNumber;
-import com.metaweb.gridworks.expr.functions.ToString;
-import com.metaweb.gridworks.expr.functions.ToTitlecase;
-import com.metaweb.gridworks.expr.functions.ToUppercase;
 
 public class Parser {
 	protected Scanner 	_scanner;
 	protected Token 	_token;
 	protected Evaluable _root;
 	
-	static public Map<String, Function> functionTable = new HashMap<String, Function>();
+	static public class ParserException extends Exception {
-    static public Map<String, Control> controlTable = new HashMap<String, Control>();
+        private static final long serialVersionUID = 155004505172098755L;
-    
-	static {
-		functionTable.put("toString", new ToString());
-		functionTable.put("toNumber", new ToNumber());
-		
-		functionTable.put("toUppercase", new ToUppercase());
-		functionTable.put("toLowercase", new ToLowercase());
-		functionTable.put("toTitlecase", new ToTitlecase());
-		
-		functionTable.put("get", new Get());
-		functionTable.put("slice", new Slice());
-		functionTable.put("substring", new Slice());
-		functionTable.put("replace", new Replace());
-		functionTable.put("split", new Split());
-		functionTable.put("length", new Length());
-		
-		functionTable.put("indexOf", new IndexOf());
-		functionTable.put("lastIndexOf", new LastIndexOf());
-		functionTable.put("startsWith", new StartsWith());
-		functionTable.put("endsWith", new EndsWith());
-		functionTable.put("join", new Join());
-		functionTable.put("reverse", new Reverse());
-		functionTable.put("sort", new Sort());
-		
-		functionTable.put("round", new Round());
-		functionTable.put("floor", new Floor());
-		functionTable.put("ceil", new Ceil());
-		functionTable.put("mod", new Mod());
-		functionTable.put("max", new Max());
-		functionTable.put("min", new Min());
-		functionTable.put("log", new Log());
-		functionTable.put("ln", new Ln());
-		
-		functionTable.put("and", new And());
-		functionTable.put("or", new Or());
-		functionTable.put("not", new Not());
-		functionTable.put("isNull", new IsNull());
-		functionTable.put("isNotNull", new IsNotNull());
-        functionTable.put("isBlank", new IsBlank());
-        functionTable.put("isNotBlank", new IsNotBlank());
 
-        controlTable.put("if", new If());
+        protected ParserException(String message) {
-        controlTable.put("with", new With());
+	        super(message);
-        controlTable.put("forEach", new ForEach());
+	    }
-        controlTable.put("forNonBlank", new ForNonBlank());
+	}
-    }
+	
-    
+	public Parser(String s) throws ParserException {
-	public Parser(String s) throws Exception {
 		this(s, 0, s.length());
 	}
 	
-	public Parser(String s, int from, int to) throws Exception {
+	public Parser(String s, int from, int to) throws ParserException {
 		_scanner = new Scanner(s, from, to);
 		_token = _scanner.next();
 		
@@ -118,13 +39,13 @@ public class Parser {
 		_token = _scanner.next();
 	}
 	
-	protected Exception makeException(String desc) {
+	protected ParserException makeException(String desc) {
 		int index = _token != null ? _token.start : _scanner.getIndex();
 		
-		return new Exception("Parsing error at offset " + index + ": " + desc);
+		return new ParserException("Parsing error at offset " + index + ": " + desc);
 	}
 	
-	protected Evaluable parseExpression() throws Exception {
+	protected Evaluable parseExpression() throws ParserException {
 		Evaluable sub = parseSubExpression();
 		
 		while (_token != null && 
@@ -143,7 +64,7 @@ public class Parser {
 		return sub;
 	}
 	
-	protected Evaluable parseSubExpression() throws Exception {
+	protected Evaluable parseSubExpression() throws ParserException {
 		Evaluable sub = parseTerm();
 		
 		while (_token != null && 
@@ -162,7 +83,7 @@ public class Parser {
 		return sub;
 	}
 	
-	protected Evaluable parseTerm() throws Exception {
+	protected Evaluable parseTerm() throws ParserException {
 		Evaluable factor = parseFactor();
 		
 		while (_token != null && 
@@ -181,7 +102,7 @@ public class Parser {
 		return factor;
 	}
 	
-	protected Evaluable parseFactor() throws Exception {
+	protected Evaluable parseFactor() throws ParserException {
 		if (_token == null) {
 			throw makeException("Expression ends too early");
 		}
@@ -210,8 +131,8 @@ public class Parser {
 			if (_token == null || _token.type != TokenType.Delimiter || !_token.text.equals("(")) {
 				eval = new VariableExpr(text);
 			} else {
-				Function f = functionTable.get(text);
+				Function f = ControlFunctionRegistry.getFunction(text);
-				Control c = controlTable.get(text);
+				Control c = ControlFunctionRegistry.getControl(text);
 				if (f == null && c == null) {
 					throw makeException("Unknown function or control named " + text);
 				}
@@ -221,7 +142,12 @@ public class Parser {
 				List<Evaluable> args = parseExpressionList(")");
 				
 				if (c != null) {
-                    eval = new ControlCallExpr(makeArray(args), c);
+				    Evaluable[] argsA = makeArray(args);
+				    String errorMessage = c.checkArguments(argsA);
+				    if (errorMessage != null) {
+				        throw makeException(errorMessage);
+				    }
+                    eval = new ControlCallExpr(argsA, c);
 				} else {
 				    eval = new FunctionCallExpr(makeArray(args), f);
 				}
@@ -254,7 +180,7 @@ public class Parser {
 				if (_token != null && _token.type == TokenType.Delimiter && _token.text.equals("(")) {
 					next(); // swallow (
 					
-					Function f = functionTable.get(identifier);
+					Function f = ControlFunctionRegistry.getFunction(identifier);
 					if (f == null) {
 						throw makeException("Unknown function " + identifier);
 					}
@@ -272,7 +198,7 @@ public class Parser {
 				List<Evaluable> args = parseExpressionList("]");
 				args.add(0, eval);
 				
-				eval = new FunctionCallExpr(makeArray(args), functionTable.get("get"));
+				eval = new FunctionCallExpr(makeArray(args), ControlFunctionRegistry.getFunction("get"));
 			} else {
 				break;
 			}
@@ -281,7 +207,7 @@ public class Parser {
 		return eval;
 	}
 	
-	protected List<Evaluable> parseExpressionList(String closingDelimiter) throws Exception {
+	protected List<Evaluable> parseExpressionList(String closingDelimiter) throws ParserException {
 		List<Evaluable> l = new LinkedList<Evaluable>();
 		
 		if (_token != null && 

src/main/java/com/metaweb/gridworks/expr/VariableExpr.java

@@ -10,7 +10,11 @@ public class VariableExpr implements Evaluable {
 	}
 	
 	public Object evaluate(Properties bindings) {
-		return bindings.get(_name);
+	    if (bindings.containsKey(_name)) {
+	        return bindings.get(_name);
+	    } else {
+	        return new EvalError("No variable named " + _name);
+	    }
 	}
 
 	public String toString() {

src/main/java/com/metaweb/gridworks/expr/controls/ForEach.java

@@ -8,50 +8,53 @@ import org.json.JSONException;
 import org.json.JSONWriter;
 
 import com.metaweb.gridworks.expr.Control;
+import com.metaweb.gridworks.expr.EvalError;
 import com.metaweb.gridworks.expr.Evaluable;
+import com.metaweb.gridworks.expr.ExpressionUtils;
 import com.metaweb.gridworks.expr.VariableExpr;
 
 public class ForEach implements Control {
-
+    public String checkArguments(Evaluable[] args) {
-    public Object call(Properties bindings, Evaluable[] args) {
+        if (args.length != 3) {
-        if (args.length >= 3) {
+            return "forEach expects 3 arguments";
-            Object o = args[0].evaluate(bindings);
+        } else if (!(args[1] instanceof VariableExpr)) {
-            Evaluable var = args[1];
+            return "forEach expects second argument to be a variable name";
-            String name = (var instanceof VariableExpr) ? ((VariableExpr) var).getName() :
-                ((String) var.evaluate(bindings));
-            
-            if (o != null) {
-                Object oldValue = bindings.get(name);
-                try {
-                    Object[] values;
-                    if (o.getClass().isArray()) {
-                        values = (Object[]) o;
-                    } else {
-                        values = new Object[] { o };
-                    }
-            
-                    List<Object> results = new ArrayList<Object>(values.length);
-                    for (Object v : values) {
-                        bindings.put(name, v);
-                        
-                        Object r = args[2].evaluate(bindings);
-                        if (r != null) {
-                            results.add(r);
-                        }
-                    }
-                    
-                    return results.toArray(); 
-                } finally {
-                	if (oldValue != null) {
-                		bindings.put(name, oldValue);
-                	} else {
-                		bindings.remove(name);
-                	}
-                }
-            }
         }
         return null;
     }
+
+    public Object call(Properties bindings, Evaluable[] args) {
+        Object o = args[0].evaluate(bindings);
+        if (ExpressionUtils.isError(o)) {
+            return o;
+        } else if (o == null || !o.getClass().isArray()) {
+            return new EvalError("First argument to forEach is not an array");
+        }
+        
+        String name = ((VariableExpr) args[1]).getName();
+        
+        Object oldValue = bindings.get(name);
+        try {
+            Object[] values = (Object[]) o;
+    
+            List<Object> results = new ArrayList<Object>(values.length);
+            for (Object v : values) {
+                bindings.put(name, v);
+                
+                Object r = args[2].evaluate(bindings);
+                
+                results.add(r);
+            }
+            
+            return results.toArray(); 
+        } finally {
+        	if (oldValue != null) {
+        		bindings.put(name, oldValue);
+        	} else {
+        		bindings.remove(name);
+        	}
+        }
+    }
     
 	public void write(JSONWriter writer, Properties options)
 		throws JSONException {

src/main/java/com/metaweb/gridworks/expr/controls/ForNonBlank.java

@@ -11,33 +11,38 @@ import com.metaweb.gridworks.expr.ExpressionUtils;
 import com.metaweb.gridworks.expr.VariableExpr;
 
 public class ForNonBlank implements Control {
-
+    public String checkArguments(Evaluable[] args) {
-    public Object call(Properties bindings, Evaluable[] args) {
+        if (args.length != 4) {
-        if (args.length >= 3) {
+            return "forNonBlank expects 4 arguments";
-            Object o = args[0].evaluate(bindings);
+        } else if (!(args[1] instanceof VariableExpr)) {
-            Evaluable var = args[1];
+            return "forNonBlank expects second argument to be a variable name";
-            String name = (var instanceof VariableExpr) ? ((VariableExpr) var).getName() :
-                ((String) var.evaluate(bindings));
-            
-            if (!ExpressionUtils.isBlank(o)) {
-                Object oldValue = bindings.containsKey(name) ? bindings.get(name) : null;
-                bindings.put(name, o);
-                
-                try {
-                    return args[2].evaluate(bindings);
-                } finally {
-                    if (oldValue != null) {
-                        bindings.put(name, oldValue);
-                    } else {
-                        bindings.remove(name);
-                    }
-                }
-            } else if (args.length >= 4) {
-                return args[3].evaluate(bindings);
-            }
         }
         return null;
     }
+    
+    public Object call(Properties bindings, Evaluable[] args) {
+        Object o = args[0].evaluate(bindings);
+        
+        Evaluable var = args[1];
+        String name = ((VariableExpr) var).getName();
+        
+        if (ExpressionUtils.isNonBlankData(o)) {
+            Object oldValue = bindings.containsKey(name) ? bindings.get(name) : null;
+            bindings.put(name, o);
+            
+            try {
+                return args[2].evaluate(bindings);
+            } finally {
+                if (oldValue != null) {
+                    bindings.put(name, oldValue);
+                } else {
+                    bindings.remove(name);
+                }
+            }
+        } else {
+            return args[3].evaluate(bindings);
+        }
+    }
 
 	public void write(JSONWriter writer, Properties options)
 		throws JSONException {

src/main/java/com/metaweb/gridworks/expr/controls/If.java

@@ -1,6 +1,6 @@
 package com.metaweb.gridworks.expr.controls;
 
- import java.util.Properties;
+import java.util.Properties;
 
 import org.json.JSONException;
 import org.json.JSONWriter;
@@ -10,19 +10,23 @@ import com.metaweb.gridworks.expr.Evaluable;
 import com.metaweb.gridworks.expr.ExpressionUtils;
 
 public class If implements Control {
-
+    public String checkArguments(Evaluable[] args) {
-    public Object call(Properties bindings, Evaluable[] args) {
+        if (args.length != 3) {
-        if (args.length >= 3) {
+            return "if expects 3 arguments";
-            Object o = args[0].evaluate(bindings);
-            
-            if (ExpressionUtils.isTrue(o)) {
-                return args[1].evaluate(bindings);
-            } else if (args.length >= 3) {
-                return args[2].evaluate(bindings);
-            }
         }
         return null;
     }
+
+    public Object call(Properties bindings, Evaluable[] args) {
+        Object o = args[0].evaluate(bindings);
+        if (ExpressionUtils.isError(o)) {
+            return o;
+        } else if (ExpressionUtils.isTrue(o)) {
+            return args[1].evaluate(bindings);
+        } else {
+            return args[2].evaluate(bindings);
+        }
+    }
     
 	public void write(JSONWriter writer, Properties options)
 		throws JSONException {

src/main/java/com/metaweb/gridworks/expr/controls/With.java

@@ -7,34 +7,44 @@ import org.json.JSONWriter;
 
 import com.metaweb.gridworks.expr.Control;
 import com.metaweb.gridworks.expr.Evaluable;
+import com.metaweb.gridworks.expr.ExpressionUtils;
 import com.metaweb.gridworks.expr.VariableExpr;
 
 public class With implements Control {
-
+    public String checkArguments(Evaluable[] args) {
-    public Object call(Properties bindings, Evaluable[] args) {
+        if (args.length != 3) {
-        if (args.length >= 3) {
+            return "with expects 3 arguments";
-            Object o = args[0].evaluate(bindings);
+        } else if (!(args[1] instanceof VariableExpr)) {
-            Evaluable var = args[1];
+            return "with expects second argument to be a variable name";
-            String name = (var instanceof VariableExpr) ? ((VariableExpr) var).getName() :
-                ((String) var.evaluate(bindings));
-            
-            if (o != null) {
-                Object oldValue = bindings.get(name);
-                try {
-                    bindings.put(name, o);
-                        
-                    return args[2].evaluate(bindings);
-                } finally {
-                	if (oldValue != null) {
-                		bindings.put(name, oldValue);
-                	} else {
-                		bindings.remove(name);
-                	}
-                }
-            }
         }
         return null;
     }
+
+    public Object call(Properties bindings, Evaluable[] args) {
+        Object o = args[0].evaluate(bindings);
+        if (ExpressionUtils.isError(o)) {
+            return o;
+        }
+        
+        String name = ((VariableExpr) args[1]).getName();
+        
+        Object oldValue = bindings.get(name);
+        try {
+            if (o != null) {
+                bindings.put(name, o);
+            } else {
+                bindings.remove(name);
+            }
+            
+            return args[2].evaluate(bindings);
+        } finally {
+        	if (oldValue != null) {
+        		bindings.put(name, oldValue);
+        	} else {
+        		bindings.remove(name);
+        	}
+        }
+    }
     
 	public void write(JSONWriter writer, Properties options)
 		throws JSONException {

src/main/java/com/metaweb/gridworks/expr/functions/Ceil.java

@@ -5,15 +5,17 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Ceil implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		if (args.length == 1 && args[0] instanceof Number) {
+		if (args.length == 1 && args[0] != null && args[0] instanceof Number) {
 			return (long) Math.ceil(((Number) args[0]).doubleValue());
 		}
-		return null;
+	    return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a number");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/EndsWith.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class EndsWith implements Function {
 
@@ -17,7 +19,7 @@ public class EndsWith implements Function {
 				return ((String) s1).endsWith((String) s2);
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects 2 strings");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Floor.java

@@ -5,15 +5,17 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Floor implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		if (args.length == 1 && args[0] instanceof Number) {
+		if (args.length == 1 && args[0] != null && args[0] instanceof Number) {
 			return (long) Math.floor(((Number) args[0]).doubleValue());
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a number");
 	}
 	
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/IndexOf.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class IndexOf implements Function {
 
@@ -17,7 +19,7 @@ public class IndexOf implements Function {
 				return ((String) s1).indexOf((String) s2);
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects 2 strings");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/IsBlank.java

@@ -11,7 +11,7 @@ import com.metaweb.gridworks.expr.Function;
 public class IsBlank implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		return args.length == 0 || ExpressionUtils.isBlank(args[0]);
+		return args.length == 0 || !ExpressionUtils.isNonBlankData(args[0]);
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/IsNotBlank.java

@@ -11,14 +11,14 @@ import com.metaweb.gridworks.expr.Function;
 public class IsNotBlank implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		return args.length > 0 && !ExpressionUtils.isBlank(args[0]);
+		return args.length > 0 && ExpressionUtils.isNonBlankData(args[0]);
 	}
 
 	public void write(JSONWriter writer, Properties options)
 		throws JSONException {
 	
 		writer.object();
-		writer.key("description"); writer.value("Returns whether o is not null and not an empty string");
+		writer.key("description"); writer.value("Returns whether o is not null, not an error, and not an empty string");
 		writer.key("params"); writer.value("o");
 		writer.key("returns"); writer.value("boolean");
 		writer.endObject();

src/main/java/com/metaweb/gridworks/expr/functions/Join.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Join implements Function {
 
@@ -33,7 +35,7 @@ public class Join implements Function {
 				return sb.toString();
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects an array and a string");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/LastIndexOf.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class LastIndexOf implements Function {
 
@@ -17,7 +19,7 @@ public class LastIndexOf implements Function {
 				return ((String) s1).lastIndexOf((String) s2);
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects 2 strings");
 	}
 	
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Length.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Length implements Function {
 
@@ -23,7 +25,7 @@ public class Length implements Function {
 				}
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects an array or a string");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Ln.java

@@ -5,15 +5,17 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Ln implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		if (args.length == 1 && args[0] instanceof Number) {
+		if (args.length == 1 && args[0] != null && args[0] instanceof Number) {
 			return Math.log(((Number) args[0]).doubleValue());
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a number");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Log.java

@@ -5,15 +5,17 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Log implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		if (args.length == 1 && args[0] instanceof Number) {
+		if (args.length == 1 && args[0] != null && args[0] instanceof Number) {
 			return Math.log10(((Number) args[0]).doubleValue());
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a number");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Max.java

@@ -5,17 +5,21 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Max implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		if (args.length == 2 && args[0] instanceof Number && args[1] instanceof Number) {
+		if (args.length == 2 && 
+		        args[0] != null && args[0] instanceof Number &&
+		        args[1] != null && args[1] instanceof Number) {
 			return Math.max(
 				((Number) args[0]).doubleValue(),
 				((Number) args[1]).doubleValue());
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects 2 numbers");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Min.java

@@ -5,17 +5,21 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Min implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		if (args.length == 2 && args[0] instanceof Number && args[1] instanceof Number) {
+		if (args.length == 2 && 
+		        args[0] != null && args[0] instanceof Number && 
+		        args[1] != null && args[1] instanceof Number) {
 			return Math.min(
 				((Number) args[0]).doubleValue(),
 				((Number) args[1]).doubleValue());
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects 2 numbers");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Mod.java

@@ -5,18 +5,22 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Mod implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		if (args.length == 2 && args[0] instanceof Number && args[1] instanceof Number) {
+		if (args.length == 2 && 
+		        args[0] != null && args[0] instanceof Number && 
+		        args[1] != null && args[1] instanceof Number) {
 			int a = ((Number) args[0]).intValue();
 			int b = ((Number) args[0]).intValue();
 			
 			return a % b;
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects 2 numbers");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Not.java

@@ -5,15 +5,17 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Not implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		if (args.length > 0) {
+		if (args.length == 1) {
 			return !objectToBoolean(args[0]);
 		}
-		return true;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a boolean");
 	}
 
 	public static boolean objectToBoolean(Object o) {

src/main/java/com/metaweb/gridworks/expr/functions/Replace.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Replace implements Function {
 
@@ -19,7 +21,7 @@ public class Replace implements Function {
 				return (v instanceof String ? (String) v : v.toString()).replace((String) find, (String) replace);
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects 3 strings");
 	}
 
 	

src/main/java/com/metaweb/gridworks/expr/functions/Reverse.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Reverse implements Function {
 
@@ -24,7 +26,7 @@ public class Reverse implements Function {
 				return r;
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects an array");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Round.java

@@ -5,15 +5,17 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Round implements Function {
 
 	public Object call(Properties bindings, Object[] args) {
-		if (args.length == 1 && args[0] instanceof Number) {
+		if (args.length == 1 && args[0] != null && args[0] instanceof Number) {
 			return ((Number) args[0]).longValue();
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a number");
 	}
 	
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Sort.java

@@ -6,7 +6,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Sort implements Function {
 
@@ -24,7 +26,7 @@ public class Sort implements Function {
 				return r;
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects an array");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/Split.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class Split implements Function {
 
@@ -17,7 +19,7 @@ public class Split implements Function {
 				return (v instanceof String ? (String) v : v.toString()).split((String) split);
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects 2 strings");
 	}
 	
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/StartsWith.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class StartsWith implements Function {
 
@@ -17,7 +19,7 @@ public class StartsWith implements Function {
 				return ((String) s1).startsWith((String) s2);
 			}
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects 2 strings");
 	}
 	public void write(JSONWriter writer, Properties options)
 		throws JSONException {

src/main/java/com/metaweb/gridworks/expr/functions/ToLowercase.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class ToLowercase implements Function {
 
@@ -14,7 +16,7 @@ public class ToLowercase implements Function {
 			Object o = args[0];
 			return (o instanceof String ? (String) o : o.toString()).toLowerCase();
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a string");
 	}
 	
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/ToTitlecase.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class ToTitlecase implements Function {
 
@@ -28,7 +30,7 @@ public class ToTitlecase implements Function {
 			
 			return sb.toString();
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a string");
 	}
 	
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/expr/functions/ToUppercase.java

@@ -5,7 +5,9 @@ import java.util.Properties;
 import org.json.JSONException;
 import org.json.JSONWriter;
 
+import com.metaweb.gridworks.expr.ControlFunctionRegistry;
 import com.metaweb.gridworks.expr.Function;
+import com.metaweb.gridworks.expr.EvalError;
 
 public class ToUppercase implements Function {
 
@@ -14,7 +16,7 @@ public class ToUppercase implements Function {
 			Object o = args[0];
 			return (o instanceof String ? (String) o : o.toString()).toUpperCase();
 		}
-		return null;
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a string");
 	}
 
 	public void write(JSONWriter writer, Properties options)

src/main/java/com/metaweb/gridworks/importers/ImporterUtilities.java

@@ -53,11 +53,11 @@ public class ImporterUtilities {
 			}
 			
 			Object value = parseCellValue(text);
-			if (ExpressionUtils.isBlank(value)) {
+			if (ExpressionUtils.isNonBlankData(value)) {
-                row.cells.add(null);
+                row.cells.add(new Cell(value, null));
-			} else {
-			    row.cells.add(new Cell(value, null));
                 hasData = true;
+			} else {
+                row.cells.add(null);
 			}
 		}
 		
@@ -72,11 +72,11 @@ public class ImporterUtilities {
 			String text = cells[c];
 			
             Object value = parseCellValue(text);
-            if (ExpressionUtils.isBlank(value)) {
+            if (ExpressionUtils.isNonBlankData(value)) {
-                row.cells.add(null);
-            } else {
                 row.cells.add(new Cell(value, null));
                 hasData = true;
+            } else {
+                row.cells.add(null);
             }
 		}
 		return hasData;

src/main/java/com/metaweb/gridworks/model/Project.java

@@ -92,11 +92,11 @@ public class Project implements Serializable {
 			for (int g = 0; g < keyedGroups.size(); g++) {
 				Group group = keyedGroups.get(g);
 				
-				if (ExpressionUtils.isBlank(row.getCellValue(group.keyCellIndex))) {
+				if (!ExpressionUtils.isNonBlankData(row.getCellValue(group.keyCellIndex))) {
 					int contextRowIndex = lastNonBlankRowsByGroup[g];
 					if (contextRowIndex >= 0) {
 						for (int dependentCellIndex : group.cellIndices) {
-							if (!ExpressionUtils.isBlank(row.getCellValue(dependentCellIndex))) {
+							if (ExpressionUtils.isNonBlankData(row.getCellValue(dependentCellIndex))) {
 								setRowDependency(
 									row, 
 									dependentCellIndex, 

src/main/java/com/metaweb/gridworks/model/ReconStats.java

@@ -40,7 +40,7 @@ public class ReconStats implements Serializable, Jsonizable {
     	
     	for (Row row : project.rows) {
     		Cell cell = row.getCell(cellIndex);
-    		if (cell != null && !ExpressionUtils.isBlank(cell.value)) {
+    		if (cell != null && ExpressionUtils.isNonBlankData(cell.value)) {
     			nonBlanks++;
     			
     			if (cell.recon != null) {

src/main/java/com/metaweb/gridworks/operations/MultiValuedCellJoinOperation.java

@@ -95,7 +95,7 @@ public class MultiValuedCellJoinOperation extends AbstractOperation {
 		    StringBuffer sb = new StringBuffer();
 		    for (int r3 = r; r3 < r2; r3++) {
 		        Object value = project.rows.get(r3).getCellValue(cellIndex);
-		        if (!ExpressionUtils.isBlank(value)) {
+		        if (ExpressionUtils.isNonBlankData(value)) {
 		            if (sb.length() > 0) {
 		                sb.append(_separator);
 		            }

src/main/java/com/metaweb/gridworks/operations/ReconJudgeSimilarCellsOperation.java

@@ -164,7 +164,7 @@ public class ReconJudgeSimilarCellsOperation extends EngineDependentMassCellOper
 			public boolean visit(Project project, int rowIndex, Row row, boolean contextual) {
                 Cell cell = row.getCell(_cellIndex);
                 if (cell != null && 
-                	!ExpressionUtils.isBlank(cell.value) && 
+                	ExpressionUtils.isNonBlankData(cell.value) && 
                 	_similarValue.equals(cell.value)) {
                 	
                 	Recon recon = null;

src/main/java/com/metaweb/gridworks/operations/ReconOperation.java

@@ -152,7 +152,7 @@ public class ReconOperation extends EngineDependentOperation {
 				public boolean visit(Project project, int rowIndex, Row row, boolean contextual) {
 					if (_cellIndex < row.cells.size()) {
 						Cell cell = row.cells.get(_cellIndex);
-						if (cell != null && !ExpressionUtils.isBlank(cell.value)) {
+						if (cell != null && ExpressionUtils.isNonBlankData(cell.value)) {
 							_entries.add(new ReconEntry(rowIndex, cell));
 						}
 					}

src/main/java/com/metaweb/gridworks/protograph/transpose/Transposer.java

@@ -54,7 +54,7 @@ public class Transposer {
 			CellNode node2 = (CellNode) node;
 			Column column = project.columnModel.getColumnByName(node2.columnName);
 			Cell cell = row.getCell(column.getCellIndex());
-			if (cell != null && !ExpressionUtils.isBlank(cell.value)) {
+			if (cell != null && ExpressionUtils.isNonBlankData(cell.value)) {
 				if (node2 instanceof CellTopicNode) {
 					if (!((CellTopicNode) node2).createForNoReconMatch && 
 						(cell.recon == null || cell.recon.judgment == Judgment.None)) {

src/main/webapp/scripts/dialogs/expression-preview-dialog.js

@@ -170,13 +170,13 @@ ExpressionPreviewDialog.prototype._update = function() {
             } else {
                 self._results = null;
             }
-            self._renderPreview(expression);
+            self._renderPreview(expression, data);
         },
         "json"
     );
 };
 
-ExpressionPreviewDialog.prototype._renderPreview = function(expression) {
+ExpressionPreviewDialog.prototype._renderPreview = function(expression, data) {
     var container = this._elmts.previewContainer.empty();
     var table = $('<table width="100%"></table>').appendTo(container)[0];
     
@@ -211,7 +211,10 @@ ExpressionPreviewDialog.prototype._renderPreview = function(expression) {
             var v = this._results[i];
             renderValue(tdValue, v);
         } else {
-            $('<span>error</span>').addClass("expression-preview-empty").appendTo(tdValue);
+            // error
+            
+            var message = (data.type == "parser") ? data.message : "internal error";
+            $('<span></span>').text(message).addClass("expression-preview-empty").appendTo(tdValue);
         }
     }
 };

src/site/index.html

@@ -82,11 +82,11 @@
         <td><div>
           <h2>Mac OSX</h2>
           <center>
-            <a class="download-link" href="gridworks-1.0.dmg"><table class="download-card">
+            <a class="download-link" href="gridworks-1.0a.dmg"><table class="download-card">
               <tr>
                 <td width="1%"><img src="gridworks.png" /></td>
                 <td>
-                  <h3>Gridworks-1.0.dmg</h3>
+                  <h3>Gridworks-1.0a.dmg</h3>
                   <div class="instructions">Download, open, then drag<br/>icon to Applications folder</div>
                 </td>
               </tr>
@@ -96,11 +96,11 @@
         <td><div>
           <h2>Windows</h2>
           <center>
-            <a class="download-link" href="gridworks-1.0.zip"><table class="download-card">
+            <a class="download-link" href="gridworks-1.0a.zip"><table class="download-card">
               <tr>
                 <td width="1%"><img src="gridworks.png" /></td>
                 <td>
-                  <h3>Gridworks-1.0.zip</h3>
+                  <h3>Gridworks-1.0a.zip</h3>
                   <div class="instructions">Download, unzip, and<br/>run .exe inside</div>
                 </td>
               </tr>