Added OneOf combinator and tests

src/Superpower/Parse.cs

@@ -592,5 +592,53 @@ public static TextParser<T> Return<T>(T value)
                 return Result.Value((rt.Value, ru.Value, rv.Value, rw.Value, rx.Value), input, rx.Remainder);
             };
         }
+        /// <summary>
+        /// Creates a parser which applies one of the specified parsers.
+        /// </summary>
+        /// <typeparam name="TKind">The kind of the tokens being parsed.</typeparam>
+        /// <typeparam name="T">The type of value being parsed.</typeparam>
+        /// <param name="parsers">The parsers to try from left to right.</param>
+        /// <returns>A parser which applies one of the specified parsers.</returns>
+        public static TokenListParser<TKind, T> OneOf<TKind, T>(params TokenListParser<TKind, T>[] parsers)
+        {
+            if (parsers == null) throw new ArgumentNullException(nameof(parsers));
+
+            if (parsers.Length == 0)
+            {
+                return i => TokenListParserResult.Empty<TKind, T>(TokenList<TKind>.Empty);
+            }
+
+            TokenListParser<TKind, T> c = parsers[0];
+            for (int i = 1; i < parsers.Length; i++)
+            {
+                c = c.Or(parsers[i]);
+            }
+
+            return c;
+        }
+
+        /// <summary>
+        /// Creates a parser which applies one of the specified parsers.
+        /// </summary>
+        /// <typeparam name="T">The type of value being parsed.</typeparam>
+        /// <param name="parsers">The parser to try from left to right.</param>
+        /// <returns>A parser which applies one of the specified parsers.</returns>
+        public static TextParser<T> OneOf<T>(params TextParser<T>[] parsers)
+        {
+            if (parsers == null) throw new ArgumentNullException(nameof(parsers));
+
+            if (parsers.Length == 0)
+            {
+                return i => Result.Empty<T>(TextSpan.None);
+            }
+
+            TextParser<T> c = parsers[0];
+            for (int i = 1; i < parsers.Length; i++)
+            {
+                c = c.Or(parsers[i]);
+            }
+
+            return c;
+        }
     }
 }

test/Superpower.Tests/Combinators/OneOfCombinatorTests.cs

@@ -0,0 +1,37 @@
+using Superpower.Model;
+using Superpower.Parsers;
+using Superpower.Tests.Support;
+using System.Linq;
+using Xunit;
+
+namespace Superpower.Tests.Combinators
+{
+    public class OneOfCombinatorTests
+    {
+        [Fact]
+        public void OneOf2Succeeds()
+        {
+            var p = Parse.OneOf(Character.Digit, Character.AnyChar);
+            AssertParser.SucceedsWithAll(Span.MatchedBy(p), "1");
+            AssertParser.SucceedsWithAll(Span.MatchedBy(p), "w");
+        }
+
+        [Fact]
+        public void OneOf2TokenSucceeds()
+        {
+            var p = Parse.OneOf(Token.EqualTo('1'), Token.EqualTo('w'));
+            AssertParser.SucceedsWith(p, "1", '1');
+            AssertParser.SucceedsWith(p, "w", 'w');
+        }
+
+        [Fact]
+        public void OneOfReportsCorrectError()
+        {
+            var names = new[] { "one", "two" };
+            TextParser<TextSpan> p = Parse.OneOf(names.Select(Span.EqualTo).ToArray());
+            AssertParser.SucceedsWith(p.Select(t => t.ToStringValue()), "one", "one");
+            AssertParser.SucceedsWith(p.Select(t => t.ToStringValue()), "two", "two");
+            AssertParser.FailsWithMessage(p.Select(t => t.ToStringValue()), "four", "Syntax error (line 1, column 1): unexpected `f`, expected `one` or `two`.");
+        }
+    }
+}