Added externally_called declaration

To suppress unused predicate warnings for predicates that are intended
to be called from the repl or from C#

Author: ianhorswill

BotL/Compiler/Compiler.cs

@@ -178,6 +178,15 @@ private static bool ProcessDeclaration(object maybeDeclaration)
                 }
                     break;
 
+                case "externally_called":
+                    {
+                        var spec = arg as Call;
+                        if (spec == null || !spec.IsFunctor(Symbol.Slash, 2))
+                            throw new ArgumentException("Invalid predicate specified in externally_called declaration");
+                        KB.Predicate((Symbol)spec.Arguments[0], (int)spec.Arguments[1]).IsExternallyCalled = true;
+                    }
+                    break;
+
                 default:
                     return false;
             }

BotL/Compiler/Lint.cs

@@ -29,7 +29,7 @@ private static void PrintClauseWarnings(TextWriter output)
         private static void WarnUnreferenced(TextWriter output, Dictionary<Predicate, List<Predicate>> refs)
         {
             foreach (var p in KB.AllRulePredicates)
-                if (p.IsUserDefined && !refs.ContainsKey(p))
+                if (p.IsUserDefined && !refs.ContainsKey(p) && !p.IsExternallyCalled)
                     Warn(output, "unused predicate {0}", p);
         }
 

BotL/Engine/Predicate.cs

@@ -157,6 +157,7 @@ internal IEnumerable<Predicate> ReferencedUserPredicates
 
         public bool IsUserDefined => (IsRulePredicate && !IsLocked) || IsTable;
         public bool IsTable => Table != null;
+        public bool IsExternallyCalled;
 
         #endregion
 

BotL/Parser/ExpressionParser.cs

@@ -52,6 +52,7 @@ static ExpressionParser()
             DefinePrefixOperator("signature", 25);
             DefinePrefixOperator("trace", 25);
             DefinePrefixOperator("notrace", 25);
+            DefinePrefixOperator("externally_called", 25);
 
             DefineBinaryOperator("=", 30);
             DefineBinaryOperator("+=", 30);

BotL/Repl.cs

@@ -117,7 +117,8 @@ public static bool RunCommand(string command)
                     }
                     else if (command.StartsWith("table ") || command.StartsWith("function ")
                              || command.StartsWith("trace ") || command.StartsWith("notrace ") 
-                             || command.StartsWith("global ") || command.StartsWith("require "))
+                             || command.StartsWith("global ") || command.StartsWith("require ")
+                             || command.StartsWith("externally_called "))
                     {
                         // Process a declaration
                         try