minor refactor of function support; start adding top level docs for evaluation support

git-svn-id: https://svn.code.sf.net/p/jackcess/code/jackcess/trunk@1190 f203690c-595d-4dc9-a70b-905162fa7fd2

6 files changed, 301 insertions, 265 deletions

diff --git a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultDateFunctions.java b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultDateFunctions.java
index ac5313c..83c6ee8 100644
--- a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultDateFunctions.java
+++ b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultDateFunctions.java
@@ -28,6 +28,7 @@ import com.healthmarketscience.jackcess.expr.Function;
 import com.healthmarketscience.jackcess.expr.Value;
 import com.healthmarketscience.jackcess.impl.ColumnImpl;
 import static com.healthmarketscience.jackcess.impl.expr.DefaultFunctions.*;
+import static com.healthmarketscience.jackcess.impl.expr.FunctionSupport.*;
 
 /**
  *
diff --git a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFinancialFunctions.java b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFinancialFunctions.java
index 4fe59ec..df397b0 100644
--- a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFinancialFunctions.java
+++ b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFinancialFunctions.java
@@ -21,12 +21,13 @@ import com.healthmarketscience.jackcess.expr.EvalContext;
 import com.healthmarketscience.jackcess.expr.Function;
 import com.healthmarketscience.jackcess.expr.Value;
 import static com.healthmarketscience.jackcess.impl.expr.DefaultFunctions.*;
+import static com.healthmarketscience.jackcess.impl.expr.FunctionSupport.*;
 
 /**
  *
  * @author James Ahlborn
  */
-public class DefaultFinancialFunctions 
+public class DefaultFinancialFunctions
 {
   /** 0 - payment end of month (default) */
   private static final int PMT_END_MNTH = 0;
@@ -39,14 +40,14 @@ public class DefaultFinancialFunctions
   static void init() {
     // dummy method to ensure this class is loaded
   }
-  
+
 
   public static final Function NPER = registerFunc(new FuncVar("NPer", 3, 5) {
     @Override
     protected Value evalVar(EvalContext ctx, Value[] params) {
-      double rate = params[0].getAsDouble(); 
-      double pmt = params[1].getAsDouble(); 
-      double pv = params[2].getAsDouble(); 
+      double rate = params[0].getAsDouble();
+      double pmt = params[1].getAsDouble();
+      double pv = params[2].getAsDouble();
 
       double fv = 0d;
       if(params.length > 3) {
@@ -71,9 +72,9 @@ public class DefaultFinancialFunctions
   public static final Function FV = registerFunc(new FuncVar("FV", 3, 5) {
     @Override
     protected Value evalVar(EvalContext ctx, Value[] params) {
-      double rate = params[0].getAsDouble(); 
-      double nper = params[1].getAsDouble(); 
-      double pmt = params[2].getAsDouble(); 
+      double rate = params[0].getAsDouble();
+      double nper = params[1].getAsDouble();
+      double pmt = params[2].getAsDouble();
 
       double pv = 0d;
       if(params.length > 3) {
@@ -98,9 +99,9 @@ public class DefaultFinancialFunctions
   public static final Function PV = registerFunc(new FuncVar("PV", 3, 5) {
     @Override
     protected Value evalVar(EvalContext ctx, Value[] params) {
-      double rate = params[0].getAsDouble(); 
-      double nper = params[1].getAsDouble(); 
-      double pmt = params[2].getAsDouble(); 
+      double rate = params[0].getAsDouble();
+      double nper = params[1].getAsDouble();
+      double pmt = params[2].getAsDouble();
 
       double fv = 0d;
       if(params.length > 3) {
@@ -125,9 +126,9 @@ public class DefaultFinancialFunctions
   public static final Function PMT = registerFunc(new FuncVar("Pmt", 3, 5) {
     @Override
     protected Value evalVar(EvalContext ctx, Value[] params) {
-      double rate = params[0].getAsDouble(); 
-      double nper = params[1].getAsDouble(); 
-      double pv = params[2].getAsDouble(); 
+      double rate = params[0].getAsDouble();
+      double nper = params[1].getAsDouble();
+      double pv = params[2].getAsDouble();
 
       double fv = 0d;
       if(params.length > 3) {
@@ -153,10 +154,10 @@ public class DefaultFinancialFunctions
   // public static final Function IPMT = registerFunc(new FuncVar("IPmt", 4, 6) {
   //   @Override
   //   protected Value evalVar(EvalContext ctx, Value[] params) {
-  //     double rate = params[0].getAsDouble(); 
-  //     double per = params[1].getAsDouble(); 
-  //     double nper = params[2].getAsDouble(); 
-  //     double pv = params[3].getAsDouble(); 
+  //     double rate = params[0].getAsDouble();
+  //     double per = params[1].getAsDouble();
+  //     double nper = params[2].getAsDouble();
+  //     double pv = params[3].getAsDouble();
 
   //     double fv = 0d;
   //     if(params.length > 4) {
@@ -184,10 +185,10 @@ public class DefaultFinancialFunctions
   // public static final Function PPMT = registerFunc(new FuncVar("PPmt", 4, 6) {
   //   @Override
   //   protected Value evalVar(EvalContext ctx, Value[] params) {
-  //     double rate = params[0].getAsDouble(); 
-  //     double per = params[1].getAsDouble(); 
-  //     double nper = params[2].getAsDouble(); 
-  //     double pv = params[3].getAsDouble(); 
+  //     double rate = params[0].getAsDouble();
+  //     double per = params[1].getAsDouble();
+  //     double nper = params[2].getAsDouble();
+  //     double pv = params[3].getAsDouble();
 
   //     double fv = 0d;
   //     if(params.length > 4) {
@@ -216,10 +217,10 @@ public class DefaultFinancialFunctions
   // public static final Function DDB = registerFunc(new FuncVar("DDB", 4, 5) {
   //   @Override
   //   protected Value evalVar(EvalContext ctx, Value[] params) {
-  //     double cost = params[0].getAsDouble(); 
-  //     double salvage = params[1].getAsDouble(); 
-  //     double life = params[2].getAsDouble(); 
-  //     double period = params[3].getAsDouble(); 
+  //     double cost = params[0].getAsDouble();
+  //     double salvage = params[1].getAsDouble();
+  //     double life = params[2].getAsDouble();
+  //     double period = params[3].getAsDouble();
 
   //     double factor = 2d;
   //     if(params.length > 4) {
@@ -259,34 +260,34 @@ public class DefaultFinancialFunctions
   // });
 
   // FIXME, untested
-  public static final Function SLN = registerFunc(new FuncVar("SLN", 3, 3) {
-    @Override
-    protected Value evalVar(EvalContext ctx, Value[] params) {
-      double cost = params[0].getAsDouble(); 
-      double salvage = params[1].getAsDouble(); 
-      double life = params[2].getAsDouble(); 
+  // public static final Function SLN = registerFunc(new FuncVar("SLN", 3, 3) {
+  //   @Override
+  //   protected Value evalVar(EvalContext ctx, Value[] params) {
+  //     double cost = params[0].getAsDouble();
+  //     double salvage = params[1].getAsDouble();
+  //     double life = params[2].getAsDouble();
 
-      double result = calculateStraightLineDepreciation(cost, salvage, life);
+  //     double result = calculateStraightLineDepreciation(cost, salvage, life);
 
-      return BuiltinOperators.toValue(result);
-    }
-  });
+  //     return BuiltinOperators.toValue(result);
+  //   }
+  // });
 
   // FIXME, untested
-  public static final Function SYD = registerFunc(new FuncVar("SYD", 4, 4) {
-    @Override
-    protected Value evalVar(EvalContext ctx, Value[] params) {
-      double cost = params[0].getAsDouble(); 
-      double salvage = params[1].getAsDouble(); 
-      double life = params[2].getAsDouble(); 
-      double period = params[3].getAsDouble(); 
+  // public static final Function SYD = registerFunc(new FuncVar("SYD", 4, 4) {
+  //   @Override
+  //   protected Value evalVar(EvalContext ctx, Value[] params) {
+  //     double cost = params[0].getAsDouble();
+  //     double salvage = params[1].getAsDouble();
+  //     double life = params[2].getAsDouble();
+  //     double period = params[3].getAsDouble();
 
-      double result = calculateSumOfYearsDepreciation(
-          cost, salvage, life, period);
+  //     double result = calculateSumOfYearsDepreciation(
+  //         cost, salvage, life, period);
 
-      return BuiltinOperators.toValue(result);
-    }
-  });
+  //     return BuiltinOperators.toValue(result);
+  //   }
+  // });
 
 
   private static double calculateLoanPaymentPeriods(
@@ -300,9 +301,9 @@ public class DefaultFinancialFunctions
     }
 
     double v1 = Math.log(1d + (rate * pv / pmt));
-      
+
     double v2 = Math.log(1d + rate);
-      
+
     double result = -v1 / v2;
 
     if(pmtType == PMT_BEG_MNTH) {
@@ -326,7 +327,7 @@ public class DefaultFinancialFunctions
     double v1 = Math.log(1d - (rate * fv / pmt));
 
     double v2 = Math.log(1d + rate);
-      
+
     double result = v1 / v2;
 
     if(pmtType == PMT_BEG_MNTH) {
@@ -374,7 +375,7 @@ public class DefaultFinancialFunctions
     }
 
     return result;
-  } 
+  }
 
   private static double calculateAnnuityPayment(
       double rate, double nper, double fv, int pmtType) {
@@ -386,7 +387,7 @@ public class DefaultFinancialFunctions
     }
 
     return result;
-  } 
+  }
 
   private static double calculateInterestPayment(
       double pmt, double rate, double per, double pv, int pmtType) {
@@ -404,7 +405,7 @@ public class DefaultFinancialFunctions
       fvPer -= 1d;
     }
 
-    double remBalance = (pv * Math.pow((1d + rate), pvPer)) - 
+    double remBalance = (pv * Math.pow((1d + rate), pvPer)) -
       // FIXME, always use pmtType of 0?
       calculateFutureValue(rate, fvPer, pmt, PMT_END_MNTH);
 
@@ -437,4 +438,3 @@ public class DefaultFinancialFunctions
   }
 
 }
-
diff --git a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFunctions.java b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFunctions.java
index f77e0a3..bfbf105 100644
--- a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFunctions.java
+++ b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFunctions.java
@@ -17,7 +17,6 @@ limitations under the License.
 package com.healthmarketscience.jackcess.impl.expr;
 
 import java.math.BigDecimal;
-import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -28,6 +27,7 @@ import com.healthmarketscience.jackcess.expr.FunctionLookup;
 import com.healthmarketscience.jackcess.expr.Value;
 import com.healthmarketscience.jackcess.impl.DatabaseImpl;
 import com.healthmarketscience.jackcess.impl.NumberFormatter;
+import static com.healthmarketscience.jackcess.impl.expr.FunctionSupport.*;
 
 /**
  *
@@ -38,8 +38,6 @@ public class DefaultFunctions
   private static final Map<String,Function> FUNCS =
     new HashMap<String,Function>();
 
-  private static final char NON_VAR_SUFFIX = '$';
-
   static {
     // load all default functions
     DefaultTextFunctions.init();
@@ -57,212 +55,6 @@ public class DefaultFunctions
   private DefaultFunctions() {}
 
 
-  public static abstract class BaseFunction implements Function
-  {
-    private final String _name;
-    private final int _minParams;
-    private final int _maxParams;
-
-    protected BaseFunction(String name, int minParams, int maxParams)
-    {
-      _name = name;
-      _minParams = minParams;
-      _maxParams = maxParams;
-    }
-
-    public String getName() {
-      return _name;
-    }
-
-    public boolean isPure() {
-      // most functions are probably pure, so make this the default
-      return true;
-    }
-
-    protected void validateNumParams(Value[] params) {
-      int num = params.length;
-      if((num < _minParams) || (num > _maxParams)) {
-        String range = ((_minParams == _maxParams) ? "" + _minParams :
-                        _minParams + " to " + _maxParams);
-        throw new EvalException(
-            "Invalid number of parameters " +
-            num + " passed, expected " + range);
-      }
-    }
-
-    protected EvalException invalidFunctionCall(
-        Throwable t, Value[] params)
-    {
-      String paramStr = Arrays.toString(params);
-      String msg = "Invalid function call {" + _name + "(" +
-        paramStr.substring(1, paramStr.length() - 1) + ")}";
-      return new EvalException(msg, t);
-    }
-
-    @Override
-    public String toString() {
-      return getName() + "()";
-    }
-  }
-
-  public static abstract class Func0 extends BaseFunction
-  {
-    protected Func0(String name) {
-      super(name, 0, 0);
-    }
-
-    @Override
-    public boolean isPure() {
-      // 0-arg functions are usually not pure
-      return false;
-    }
-
-    public final Value eval(EvalContext ctx, Value... params) {
-      try {
-        validateNumParams(params);
-        return eval0(ctx);
-      } catch(Exception e) {
-        throw invalidFunctionCall(e, params);
-      }
-    }
-
-    protected abstract Value eval0(EvalContext ctx);
-  }
-
-  public static abstract class Func1 extends BaseFunction
-  {
-    protected Func1(String name) {
-      super(name, 1, 1);
-    }
-
-    public final Value eval(EvalContext ctx, Value... params) {
-      try {
-        validateNumParams(params);
-        return eval1(ctx, params[0]);
-      } catch(Exception e) {
-        throw invalidFunctionCall(e, params);
-      }
-    }
-
-    protected abstract Value eval1(EvalContext ctx, Value param);
-  }
-
-  public static abstract class Func1NullIsNull extends BaseFunction
-  {
-    protected Func1NullIsNull(String name) {
-      super(name, 1, 1);
-    }
-
-    public final Value eval(EvalContext ctx, Value... params) {
-      try {
-        validateNumParams(params);
-        Value param1 = params[0];
-        if(param1.isNull()) {
-          return param1;
-        }
-        return eval1(ctx, param1);
-      } catch(Exception e) {
-        throw invalidFunctionCall(e, params);
-      }
-    }
-
-    protected abstract Value eval1(EvalContext ctx, Value param);
-  }
-
-  public static abstract class Func2 extends BaseFunction
-  {
-    protected Func2(String name) {
-      super(name, 2, 2);
-    }
-
-    public final Value eval(EvalContext ctx, Value... params) {
-      try {
-        validateNumParams(params);
-        return eval2(ctx, params[0], params[1]);
-      } catch(Exception e) {
-        throw invalidFunctionCall(e, params);
-      }
-    }
-
-    protected abstract Value eval2(EvalContext ctx, Value param1, Value param2);
-  }
-
-  public static abstract class Func3 extends BaseFunction
-  {
-    protected Func3(String name) {
-      super(name, 3, 3);
-    }
-
-    public final Value eval(EvalContext ctx, Value... params) {
-      try {
-        validateNumParams(params);
-        return eval3(ctx, params[0], params[1], params[2]);
-      } catch(Exception e) {
-        throw invalidFunctionCall(e, params);
-      }
-    }
-
-    protected abstract Value eval3(EvalContext ctx,
-                                   Value param1, Value param2, Value param3);
-  }
-
-  public static abstract class FuncVar extends BaseFunction
-  {
-    protected FuncVar(String name) {
-      super(name, 0, Integer.MAX_VALUE);
-    }
-
-    protected FuncVar(String name, int minParams, int maxParams) {
-      super(name, minParams, maxParams);
-    }
-
-    public final Value eval(EvalContext ctx, Value... params) {
-      try {
-        validateNumParams(params);
-        return evalVar(ctx, params);
-      } catch(Exception e) {
-        throw invalidFunctionCall(e, params);
-      }
-    }
-
-    protected abstract Value evalVar(EvalContext ctx, Value[] params);
-  }
-
-  public static class StringFuncWrapper implements Function
-  {
-    private final String _name;
-    private final Function _delegate;
-
-    public StringFuncWrapper(Function delegate) {
-      _delegate = delegate;
-      _name = _delegate.getName() + NON_VAR_SUFFIX;
-    }
-
-    public String getName() {
-      return _name;
-    }
-
-    public boolean isPure() {
-      return _delegate.isPure();
-    }
-
-    public Value eval(EvalContext ctx, Value... params) {
-      Value result = _delegate.eval(ctx, params);
-      if(result.isNull()) {
-        // non-variant version does not do null-propagation, so force
-        // exception to be thrown here
-        result.getAsString();
-      }
-      return result;
-    }
-
-    @Override
-    public String toString() {
-      return getName() + "()";
-    }
-  }
-
-
   public static final Function IIF = registerFunc(new Func3("IIf") {
     @Override
     protected Value eval3(EvalContext ctx,
diff --git a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultNumberFunctions.java b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultNumberFunctions.java
index d93463f..aeca27d 100644
--- a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultNumberFunctions.java
+++ b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultNumberFunctions.java
@@ -24,6 +24,7 @@ import com.healthmarketscience.jackcess.expr.Function;
 import com.healthmarketscience.jackcess.expr.Value;
 import com.healthmarketscience.jackcess.impl.NumberFormatter;
 import static com.healthmarketscience.jackcess.impl.expr.DefaultFunctions.*;
+import static com.healthmarketscience.jackcess.impl.expr.FunctionSupport.*;
 
 /**
  *
@@ -185,7 +186,7 @@ public class DefaultNumberFunctions
   });
 
 
-  // public static final Function Val = registerFunc(new Func1("Val") {
+  // public static final Function VAL = registerFunc(new Func1("Val") {
   //   @Override
   //   protected Value eval1(EvalContext ctx, Value param1) {
   //     // FIXME, maybe leverage ExpressionTokenizer.maybeParseNumberLiteral (note, leading - or + is valid, exponent form is valid)
diff --git a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultTextFunctions.java b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultTextFunctions.java
index de1159a..18f7c1f 100644
--- a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultTextFunctions.java
+++ b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultTextFunctions.java
@@ -23,6 +23,7 @@ import com.healthmarketscience.jackcess.expr.EvalException;
 import com.healthmarketscience.jackcess.expr.Function;
 import com.healthmarketscience.jackcess.expr.Value;
 import static com.healthmarketscience.jackcess.impl.expr.DefaultFunctions.*;
+import static com.healthmarketscience.jackcess.impl.expr.FunctionSupport.*;
 
 /**
  *
diff --git a/src/main/java/com/healthmarketscience/jackcess/impl/expr/FunctionSupport.java b/src/main/java/com/healthmarketscience/jackcess/impl/expr/FunctionSupport.java
new file mode 100644
index 0000000..bc87f59
--- /dev/null
+++ b/src/main/java/com/healthmarketscience/jackcess/impl/expr/FunctionSupport.java
@@ -0,0 +1,241 @@
+/*
+Copyright (c) 2018 James Ahlborn
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package com.healthmarketscience.jackcess.impl.expr;
+
+import java.util.Arrays;
+
+import com.healthmarketscience.jackcess.expr.EvalContext;
+import com.healthmarketscience.jackcess.expr.EvalException;
+import com.healthmarketscience.jackcess.expr.Function;
+import com.healthmarketscience.jackcess.expr.Value;
+
+/**
+ *
+ * @author James Ahlborn
+ */
+public class FunctionSupport
+{
+  private static final char NON_VAR_SUFFIX = '$';
+
+  private FunctionSupport() {}
+
+  public static abstract class BaseFunction implements Function
+  {
+    private final String _name;
+    private final int _minParams;
+    private final int _maxParams;
+
+    protected BaseFunction(String name, int minParams, int maxParams)
+    {
+      _name = name;
+      _minParams = minParams;
+      _maxParams = maxParams;
+    }
+
+    public String getName() {
+      return _name;
+    }
+
+    public boolean isPure() {
+      // most functions are probably pure, so make this the default
+      return true;
+    }
+
+    protected void validateNumParams(Value[] params) {
+      int num = params.length;
+      if((num < _minParams) || (num > _maxParams)) {
+        String range = ((_minParams == _maxParams) ? "" + _minParams :
+                        _minParams + " to " + _maxParams);
+        throw new EvalException(
+            "Invalid number of parameters " +
+            num + " passed, expected " + range);
+      }
+    }
+
+    protected EvalException invalidFunctionCall(
+        Throwable t, Value[] params)
+    {
+      String paramStr = Arrays.toString(params);
+      String msg = "Invalid function call {" + _name + "(" +
+        paramStr.substring(1, paramStr.length() - 1) + ")}";
+      return new EvalException(msg, t);
+    }
+
+    @Override
+    public String toString() {
+      return getName() + "()";
+    }
+  }
+
+  public static abstract class Func0 extends BaseFunction
+  {
+    protected Func0(String name) {
+      super(name, 0, 0);
+    }
+
+    @Override
+    public boolean isPure() {
+      // 0-arg functions are usually not pure
+      return false;
+    }
+
+    public final Value eval(EvalContext ctx, Value... params) {
+      try {
+        validateNumParams(params);
+        return eval0(ctx);
+      } catch(Exception e) {
+        throw invalidFunctionCall(e, params);
+      }
+    }
+
+    protected abstract Value eval0(EvalContext ctx);
+  }
+
+  public static abstract class Func1 extends BaseFunction
+  {
+    protected Func1(String name) {
+      super(name, 1, 1);
+    }
+
+    public final Value eval(EvalContext ctx, Value... params) {
+      try {
+        validateNumParams(params);
+        return eval1(ctx, params[0]);
+      } catch(Exception e) {
+        throw invalidFunctionCall(e, params);
+      }
+    }
+
+    protected abstract Value eval1(EvalContext ctx, Value param);
+  }
+
+  public static abstract class Func1NullIsNull extends BaseFunction
+  {
+    protected Func1NullIsNull(String name) {
+      super(name, 1, 1);
+    }
+
+    public final Value eval(EvalContext ctx, Value... params) {
+      try {
+        validateNumParams(params);
+        Value param1 = params[0];
+        if(param1.isNull()) {
+          return param1;
+        }
+        return eval1(ctx, param1);
+      } catch(Exception e) {
+        throw invalidFunctionCall(e, params);
+      }
+    }
+
+    protected abstract Value eval1(EvalContext ctx, Value param);
+  }
+
+  public static abstract class Func2 extends BaseFunction
+  {
+    protected Func2(String name) {
+      super(name, 2, 2);
+    }
+
+    public final Value eval(EvalContext ctx, Value... params) {
+      try {
+        validateNumParams(params);
+        return eval2(ctx, params[0], params[1]);
+      } catch(Exception e) {
+        throw invalidFunctionCall(e, params);
+      }
+    }
+
+    protected abstract Value eval2(EvalContext ctx, Value param1, Value param2);
+  }
+
+  public static abstract class Func3 extends BaseFunction
+  {
+    protected Func3(String name) {
+      super(name, 3, 3);
+    }
+
+    public final Value eval(EvalContext ctx, Value... params) {
+      try {
+        validateNumParams(params);
+        return eval3(ctx, params[0], params[1], params[2]);
+      } catch(Exception e) {
+        throw invalidFunctionCall(e, params);
+      }
+    }
+
+    protected abstract Value eval3(EvalContext ctx,
+                                   Value param1, Value param2, Value param3);
+  }
+
+  public static abstract class FuncVar extends BaseFunction
+  {
+    protected FuncVar(String name) {
+      super(name, 0, Integer.MAX_VALUE);
+    }
+
+    protected FuncVar(String name, int minParams, int maxParams) {
+      super(name, minParams, maxParams);
+    }
+
+    public final Value eval(EvalContext ctx, Value... params) {
+      try {
+        validateNumParams(params);
+        return evalVar(ctx, params);
+      } catch(Exception e) {
+        throw invalidFunctionCall(e, params);
+      }
+    }
+
+    protected abstract Value evalVar(EvalContext ctx, Value[] params);
+  }
+
+  public static class StringFuncWrapper implements Function
+  {
+    private final String _name;
+    private final Function _delegate;
+
+    public StringFuncWrapper(Function delegate) {
+      _delegate = delegate;
+      _name = _delegate.getName() + NON_VAR_SUFFIX;
+    }
+
+    public String getName() {
+      return _name;
+    }
+
+    public boolean isPure() {
+      return _delegate.isPure();
+    }
+
+    public Value eval(EvalContext ctx, Value... params) {
+      Value result = _delegate.eval(ctx, params);
+      if(result.isNull()) {
+        // non-variant version does not do null-propagation, so force
+        // exception to be thrown here
+        result.getAsString();
+      }
+      return result;
+    }
+
+    @Override
+    public String toString() {
+      return getName() + "()";
+    }
+  }
+
+}