Eval parser

NadekoBot/Modules/Searches/Commands/EvalCommand.cs

@@ -0,0 +1,88 @@
+using NadekoBot.Classes;
+using System;
+using Mathos.Parser;
+using System.Threading.Tasks;
+using Discord.Commands;
+using System.Text.RegularExpressions;
+
+namespace NadekoBot.Modules.Searches.Commands
+{
+    class EvalCommand : DiscordCommand
+    {
+        public EvalCommand(DiscordModule module) : base(module)
+        {
+        }
+
+        internal override void Init(CommandGroupBuilder cgb)
+        {
+            cgb.CreateCommand(Module.Prefix + "evaluate")
+                .Alias(Module.Prefix + "eval")
+                .Description("Evaluate a mathematical expression")
+                .Parameter("expression", ParameterType.Unparsed)
+                .Do(EvalFunc());
+        }
+
+
+        private CustomParser parser = new CustomParser();
+        private Func<CommandEventArgs, Task> EvalFunc() => async e =>
+        {
+            string expression = e.GetArg("expression")?.Trim();
+            if (string.IsNullOrWhiteSpace(expression))
+            {
+                await e.Channel.SendMessage("Must give expression");
+                return;
+            }
+            string answer = evaluate(expression);
+            if (answer == null)
+            {
+                await e.Channel.SendMessage($"Expression {expression} failed to evaluate");
+                return;
+            }
+            await e.Channel.SendMessage($"`result: {answer}`");
+        };
+
+        private string evaluate(string expression)
+        {
+            //check for factorial
+            expression = Regex.Replace(expression, @"\d+!", x => x.Value + "0");
+            try
+            {
+                string result = parser.Parse(expression).ToString();
+                return result;
+            }
+            catch (OverflowException e)
+            {
+                return $"Overflow error on {expression}";
+            }
+            catch (FormatException e)
+            {
+                return $"\"{expression}\" was not formatted correctly";
+            }
+        }
+
+        
+
+        class CustomParser : MathParser
+        {
+            public CustomParser() : base()
+            {
+                OperatorList.Add("!");
+                OperatorList.Add("_");
+                OperatorAction.Add("!", (x, y) => factorial(x));
+                OperatorAction.Add("_", (x, y) => 10.130M);
+            }
+
+            static decimal factorial(decimal x)
+            {
+                decimal y = x-1;
+                while (y >0)
+                {
+                    x = x * y--;
+                }
+                return x;
+            }
+        }
+
+
+    }
+}

NadekoBot/Modules/Searches/SearchesModule.cs

@@ -28,6 +28,7 @@ namespace NadekoBot.Modules.Searches
             commands.Add(new ConverterCommand(this));
             commands.Add(new RedditCommand(this));
 			commands.Add(new WowJokeCommand(this));
+            commands.Add(new EvalCommand(this));
             rng = new Random();
         }