Enum parser, variable case sensitive string parser (#126)

* Enum parser

* API Consistency

* Tests

* Move enum tests to StringParserTests

Pidgin.Tests/StringParserTests.cs

@@ -2506,5 +2506,31 @@ public void TestCurrentPos()
                 AssertSuccess(parser.Parse("f"), SourcePosDelta.Zero, false);  // it should backtrack
             }
         }
+
+        internal enum TestEnum
+        {
+            Value1 = 0,
+            Value2,
+            Value3
+        }  
+
+        [Fact]
+        public void EnumParseTest()
+        {
+            const string value1 = "value1";
+            var result = Parser.Enum<TestEnum>().Parse(value1);
+            Assert.False(result.Success);
+
+            result = Parser.CIEnum<TestEnum>().Parse(value1);
+            Assert.Equal(TestEnum.Value1, result.Value);
+
+            const string value2 = "Value2";
+            result = Parser.Enum<TestEnum>().Parse(value2);
+            Assert.Equal(TestEnum.Value2, result.Value);
+
+            result = Parser.CIEnum<TestEnum>().Parse(value2);
+            Assert.Equal(TestEnum.Value2, result.Value);
+
+        }
     }
 }

Pidgin/Parser.Enum.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Pidgin
+{
+    public static partial class Parser
+    {
+        /// <summary>
+        /// Creates a parser that parses and returns one of enum values
+        /// </summary>
+        /// <typeparam name="TEnum">Enum type</typeparam>
+        /// <returns>A parser that parses and returns one of enum values</returns>
+        public static Parser<char, TEnum> Enum<TEnum>()
+            where TEnum : struct, Enum
+        {
+            return OneOf(System.Enum.GetNames<TEnum>()
+                    .Select(String)
+                    .Select(Try))
+                .Select(System.Enum.Parse<TEnum>)
+                .Labelled("enum " + typeof(TEnum).Name);
+        }
+
+        /// <summary>
+        /// Creates a parser that parses and returns one of enum values, in a case insensitive manner.
+        /// </summary>
+        /// <typeparam name="TEnum">Enum type</typeparam>
+        /// <returns>A parser that parses and returns one of enum values</returns>
+        public static Parser<char, TEnum> CIEnum<TEnum>()
+            where TEnum : struct, Enum
+        {
+            return OneOf(System.Enum.GetNames<TEnum>()
+                    .Select(CIString)
+                    .Select(Try))
+                .Select(x=> System.Enum.Parse<TEnum>(x, true))
+                .Labelled("enum " + typeof(TEnum).Name);
+        }
+
+    }
+}