Added two base functions

src/core/FunctionValue.cs

@@ -12,8 +12,11 @@ namespace csmic
         public ValueType Type { get; set; }
         public object? Value { get; set; }
 
-        public static readonly FunctionValue TRUE = new FunctionValue(ValueType.Numeric, 1);
-        public static readonly FunctionValue FALSE = new FunctionValue(ValueType.Numeric, 0);
+        public static readonly FunctionValue TRUE = new FunctionValue(ValueType.Numeric, 1m);
+        public static readonly FunctionValue FALSE = new FunctionValue(ValueType.Numeric, 0m);
+        public static readonly FunctionValue NONE = new FunctionValue(ValueType.None, null);
+        public static readonly FunctionValue NUMBER = new FunctionValue(ValueType.Numeric, 0m);
+        public static readonly FunctionValue STRING = new FunctionValue(ValueType.String, string.Empty);
 
         public FunctionValue()
         {

src/stdlib/functions/AbsoluteValue.cs

@@ -5,48 +5,23 @@ namespace stdlib.functions
 {
     public class AbsoluteValue : FunctionBase, ICodedFunction
     {
-        public IEnumerable<FunctionArgument> ExpectedArguments
+        public override IEnumerable<FunctionArgument> ExpectedArguments
         {
             get
             {
-                yield return new FunctionArgument("value", new FunctionValue(ValueType.Numeric, 0m));
+                yield return new FunctionArgument("value", FunctionValue.NUMBER);
             }
         }
 
-        public FunctionValue ReturnValue
-        {
-            new FunctionValue(ValueType.Numeric, 0m);
-    }
-        => 
-
         public FunctionValue Execute(params FunctionArgument[] args)
         {
-            base.ArgumentCheck(args);
-
-            try
+            return base.Execute(args, (_args) =>
             {
-                var input = args[0].Value;
-                // Try to interpret both numeric and numeric-like string inputs
-                decimal number;
-                if (input.Type == ValueType.Numeric)
-                {
-                    number = Convert.ToDecimal(input.Value);
-                }
-                else if (input.Type == ValueType.String && input.Value is string s)
-                {
-                    number = Convert.ToDecimal(s);
-                }
-                else
-                {
-                    return new FunctionValue(ValueType.None, null);
-                }
+                var input = _args[0].Value;
+                decimal number = Convert.ToDecimal(input.Value);
 
                 return new FunctionValue(ValueType.Numeric, Math.Abs(number));
-            }
-            catch
-            {
-                return new FunctionValue(ValueType.None, null);
-            }
+            });
         }
     }
 }

src/stdlib/functions/FunctionBase.cs

@@ -7,25 +7,64 @@ namespace stdlib.functions
     {
         public virtual IEnumerable<FunctionArgument> ExpectedArguments { get; }
 
-        internal bool ArgumentCheck(params FunctionArgument[] args)
+        public virtual FunctionValue ReturnValue
         {
+            get
+
+            {
+                return FunctionValue.NUMBER;
+            }
+        }
+
+        public bool ArgumentCheck(params FunctionArgument[] args)
+        {
+            // Top level sanity checks.
             if (args == null || args.Length != this.ExpectedArguments.Count())
             {
                 return false;
             }
 
+            // Check each argument against what is expected.
             var expectedArgumentsArray = this.ExpectedArguments.ToArray();
             for (int i = 0; i < args.Length; i++)
             {
                 var expectedArgument = expectedArgumentsArray[i];
                 var argument = args[i];
-                if(argument.Value == null || argument.Value.Type != expectedArgument.Value.Type)
+                if (argument.Value == null || argument.Value.Value == null || argument.Value.Type != expectedArgument.Value.Type)
+                {
+                    return false;
+                }
+
+                if (argument.Value.Type == ValueType.Numeric && argument.Value.Value is not decimal)
+                {
+                    return false;
+                }
+
+                if (argument.Value.Type == ValueType.String && argument.Value.Value is not string)
                 {
                     return false;
                 }
             }
 
+            // All checks passed.
             return true;
         }
+
+        public FunctionValue Execute(FunctionArgument[] args, Func<FunctionArgument[], FunctionValue> action)
+        {
+            if (!ArgumentCheck(args))
+            {
+                return FunctionValue.NONE;
+            }
+
+            try
+            {
+                return action(args);
+            }
+            catch
+            {
+                return FunctionValue.NONE;
+            }
+        }
     }
 }

src/stdlib/functions/Sign.cs

@@ -0,0 +1,30 @@
+using csmic;
+using ValueType = csmic.ValueType;
+
+namespace stdlib.functions
+{
+    public class Sign : FunctionBase, ICodedFunction
+    {
+        public const decimal POSITIVE = 1;
+        public const decimal NEGATIVE = -1;
+
+        public override IEnumerable<FunctionArgument> ExpectedArguments
+        {
+            get
+            {
+                yield return new FunctionArgument("value", FunctionValue.NUMBER);
+            }
+        }
+
+        public FunctionValue Execute(params FunctionArgument[] args)
+        {
+            return base.Execute(args, (_args) =>
+            {
+                var input = _args[0].Value;
+                decimal number = Convert.ToDecimal(input.Value);
+
+                return new FunctionValue(ValueType.Numeric, number >= 0 ? POSITIVE : NEGATIVE);
+            });
+        }
+    }
+}