first version (Qiita Advent Calendar 2017)

src/ParserCombinator.Tests/CharParserTest.cs

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+using System;
+using Xunit;
+using Xunit.Abstractions;
+using static Xunit.Assert;
+using static Xunit.AssertEx;
+
+using static ParserCombinator.CharParsers;
+
+namespace ParserCombinator.Tests
+{
+    public class CharParserTest
+    {
+        [Fact]
+        public void AnyTest()
+        {
+            // Any はつねに成功
+            var result = Any(Source.Create("a"));    // { IsSuccess: true, Result: 'a' }
+            result.IsSuccess.IsTrue();
+            result.Result.Is('a');
+        }
+
+        [Fact]
+        public void DigitTest()
+        {
+            // 数字だったら成功
+            var success = Digit(Source.Create("12a"));    // { IsSuccess: true, Result: '1' }
+            success.IsSuccess.IsTrue();
+            success.Result.Is('1');
+
+            // 数字でなければ失敗
+            var failed = Digit(Source.Create("a12"));     // { IsSuccess: false, Result: Exception }
+            failed.IsSuccess.IsFalse();
+            Throws(typeof(Exception), AccessToFailedResult(failed));
+        }
+
+        [Fact]
+        public void LiteralTest()
+        {
+            var parser = Literal('a');
+            var success = parser(Source.Create("abc"));    // { IsSuccess: true, Result: 'a' }
+            success.IsSuccess.IsTrue();
+            success.Result.Is('a');
+            var failed = parser(Source.Create("ccc"));     // { IsSuccess: false, Result: Exception }
+            failed.IsSuccess.IsFalse();
+            Throws(typeof(Exception), AccessToFailedResult(failed));
+        }
+
+
+        [Fact]
+        public void IsTest()
+        {
+            var lowerParser = Is(char.IsLower);    // 小文字だけ受け付けるパーサ
+            var success = lowerParser(Source.Create("abc"));    // { IsSuccess: true, Result: 'a' }
+            var failed = lowerParser(Source.Create("ABC"));     // { IsSuccess: false, Result: Exception }
+
+            success.IsSuccess.IsTrue();
+            success.Result.Is('a');
+
+            failed.IsSuccess.IsFalse();
+            Throws(typeof(Exception), AccessToFailedResult(failed));
+        }
+
+        private static Action AccessToFailedResult<T>(ParseResult<T> result) => () =>
+        {
+            var tmp = result.Result;
+        };
+    }
+}

src/ParserCombinator.Tests/ParserCombinator.Tests.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.0</TargetFramework>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.3.0-preview-20170628-02" />
+    <PackageReference Include="xunit" Version="2.2.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.2.0" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\ParserCombinator\ParserCombinator.csproj" />
+  </ItemGroup>
+</Project>

src/ParserCombinator.Tests/PostalCodeParser.cs

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+using System;
+using System.Linq;
+using Xunit;
+using static Xunit.Assert;
+using static ParserCombinator.ParseResultHelper;
+using static ParserCombinator.CharParsers;
+
+namespace ParserCombinator.Tests
+{
+    public class PostalCodeParserTests
+    {
+        [Fact]
+        public void SimplePostalCodeParserTest()
+        {
+            // xxx-yyyy の xxx 部分
+            Parser<int> leftPart = Digit.Repeat(3).Map(chars => int.Parse(new string(chars.ToArray())));
+
+            // xxx-yyyy の yyyy 部分
+            Parser<int> rightPart = Digit.Repeat(4).Map(chars => int.Parse(new string(chars.ToArray())));
+
+            // xxx-yyyy の形式の郵便番号のパーサ
+            Parser<PostalCode> postalCodeParser = leftPart
+                .Left(Literal('-'))
+                .Sequence(rightPart, (left, right) => new PostalCode(left, right));
+
+            ParseResult<PostalCode> result = postalCodeParser(Source.Create("123-4567"));
+            PostalCode postalCode = result.Result;
+
+            result.IsSuccess.IsTrue();
+            postalCode.IsStructuralEqual(new PostalCode(123, 4567));
+        }
+
+        [Fact]
+        public void PostalCodeParserTest()
+        {
+// xxx-yyyy の xxx 部分
+Parser<int> leftPart = Digit.Repeat(3).Map(chars => int.Parse(new string(chars.ToArray())));
+
+// xxx-yyyy の yyyy 部分
+Parser<int> rightPart = Digit.Repeat(4).Map(chars => int.Parse(new string(chars.ToArray())));
+
+// 普通の xxx-yyyy
+Parser<PostalCode> normal = leftPart.Left(Literal('-')).Sequence(rightPart, (l, r) => new PostalCode(l, r));
+
+// xxxyyyy
+Parser<PostalCode> withoutSeparator = leftPart.Sequence(rightPart, (l, r) => new PostalCode(l, r));
+
+Parser<PostalCode> postalCode = normal.Or(withoutSeparator);
+
+// 〒 が付加されてもよい
+Parser<PostalCode> postalCodeParser = Literal('〒').Right(postalCode).Or(postalCode);
+
+            var expected = new PostalCode(123, 4567);
+            postalCodeParser(Source.Create("123-4567")).Result.IsStructuralEqual(expected);
+            postalCodeParser(Source.Create("1234567")).Result.IsStructuralEqual(expected);
+            postalCodeParser(Source.Create("〒123-4567")).Result.IsStructuralEqual(expected);
+            postalCodeParser(Source.Create("〒1234567")).Result.IsStructuralEqual(expected);
+        }
+    }
+
+    public class PostalCode
+    {
+        public int LeftPart { get; }
+
+        public int RightPart { get; }
+
+        public PostalCode(int left, int right)
+        {
+            this.LeftPart = left;
+            this.RightPart = right;
+        }
+
+        public override string ToString() => $"{LeftPart}-{RightPart}";
+    }
+}

src/ParserCombinator.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio 2013
+VisualStudioVersion = 12.0.0.0
+MinimumVisualStudioVersion = 10.0.0.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ParserCombinator", "ParserCombinator/ParserCombinator.csproj", "{BD5A64D0-B4CE-4130-A43B-26519E0B9665}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ParserCombinator.Tests", "ParserCombinator.Tests\ParserCombinator.Tests.csproj", "{1593751F-40C6-44DA-8D0C-B3588A0DBFEE}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{BD5A64D0-B4CE-4130-A43B-26519E0B9665}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{BD5A64D0-B4CE-4130-A43B-26519E0B9665}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{BD5A64D0-B4CE-4130-A43B-26519E0B9665}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{BD5A64D0-B4CE-4130-A43B-26519E0B9665}.Release|Any CPU.Build.0 = Release|Any CPU
+		{1593751F-40C6-44DA-8D0C-B3588A0DBFEE}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{1593751F-40C6-44DA-8D0C-B3588A0DBFEE}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{1593751F-40C6-44DA-8D0C-B3588A0DBFEE}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{1593751F-40C6-44DA-8D0C-B3588A0DBFEE}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+EndGlobal

src/ParserCombinator/CharParsers.cs

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+using System;
+
+namespace ParserCombinator
+{
+    using static ParseResultHelper;
+
+    public static class CharParsers
+    {
+        public static Parser<char> Any { get; } = (Source s) =>
+        {
+            var (c, next) = s.Read();
+            return Success(next, c);
+        };
+
+        public static Parser<char> Digit { get; } = (Source s) =>
+        {
+            var (c, next) = s.Read();
+            return char.IsDigit(c) ? Success(next, c) : Failed<char>(next, "Is not a digit.");
+        };
+
+        public static Parser<char> Literal(char literal) => (Source s) =>
+        {
+            var (c, next) = s.Read();
+            return c == literal ? Success(next, c) : Failed<char>(next, $"{c} is not equals {literal}");
+        };
+
+        public static Parser<char> Is(Func<char, bool> predicate) => (Source s) =>
+        {
+            var (c, next) = s.Read();
+            return predicate(c) ? Success(next, c) : Failed<char>(next, $"predicate({c}) returns false.");
+        };
+    }
+}

src/ParserCombinator/Combinators.cs

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+using System;
+using System.Collections.Immutable;
+using System.Net.Mime;
+using static ParserCombinator.ParseResultHelper;
+
+namespace ParserCombinator
+{
+    public static class Combinators
+    {
+public static Parser<ImmutableList<T>> Many<T>(this Parser<T> parser)
+{
+    ParseResult<ImmutableList<T>> Impl(Source s, ImmutableList<T> results)
+    {
+        var result = parser(s);
+
+        return result.IsSuccess
+            ? Impl(result.Source, results.Add(result.Result))
+            : Success(s, results);
+    }
+
+    return (Source s) => Impl(s, ImmutableList<T>.Empty);
+}
+
+        public static Parser<ImmutableList<T>> Repeat<T>(this Parser<T> parser, int count)
+        {
+            ParseResult<ImmutableList<T>> Impl(Source s, int c, ImmutableList<T> results)
+            {
+                if (c == 0)
+                {
+                    // 0 回を指定されたら終わり
+                    return Success(s, results);
+                }
+
+                var result = parser(s);
+
+                return result.IsSuccess
+                    ? Impl(result.Source, c - 1, results.Add(result.Result))
+                    : Failed<ImmutableList<T>>(result.Source, result.Reason);
+            }
+
+            return (Source s) => Impl(s, count, ImmutableList<T>.Empty);
+        }
+
+        public static Parser<ImmutableList<T>> Sequence<T>(this Parser<T> first, Parser<T> second) =>
+            first.Sequence(second, (f, s) => ImmutableList<T>.Empty.Add(f).Add(s));
+
+        public static Parser<ImmutableList<T>> Sequence<T>(this Parser<ImmutableList<T>> first, Parser<T> second) =>
+            first.Sequence(second, (f, s) => f.Add(s));
+
+        public static Parser<TResult> Sequence<TFirst, TSecond, TResult>(this Parser<TFirst> first, Parser<TSecond> second, Func<TFirst, TSecond, TResult> resultSelector) =>
+            (Source s) =>
+            {
+                var firstResult = first(s);
+                if (firstResult.IsSuccess)
+                {
+                    var secondResult = second(firstResult.Source);
+        
+                    return secondResult.IsSuccess
+                        ? Success(secondResult.Source, resultSelector(firstResult.Result, secondResult.Result))
+                        : Failed<TResult>(secondResult.Source, secondResult.Reason);
+                }
+                else
+                {
+                    return Failed<TResult>(firstResult.Source, firstResult.Reason);
+                }
+            };
+
+        public static Parser<T> Or<T>(this Parser<T> left, Parser<T> right) => (Source s) =>
+        {
+            var leftResult = left(s);
+
+            return leftResult.IsSuccess
+                ? leftResult
+                : right(s);
+        };
+
+        public static Parser<TLeft> Left<TLeft, TRight>(this Parser<TLeft> left, Parser<TRight> right) =>
+            left.Sequence(right, (l, r) => l);
+
+        public static Parser<TRight> Right<TLeft, TRight>(this Parser<TLeft> left, Parser<TRight> right) =>
+            left.Sequence(right, (l, r) => r);
+
+        public static Parser<TResult> Map<TParser, TResult>(this Parser<TParser> parser, Func<TParser, TResult> mapper) =>
+            (Source s) =>
+            {
+                var result = parser(s);
+                return result.IsSuccess
+                    ? Success(result.Source, mapper(result.Result))
+                    : Failed<TResult>(result.Source, result.Reason);
+            };
+    }
+}

src/ParserCombinator/ParseResult.cs

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+using System;
+
+namespace ParserCombinator
+{
+    public struct ParseResult<T>
+    {
+        /// <summary>実行後の Source</summary>
+        public Source Source { get; }
+
+        /// <summary>成功したかどうか</summary>
+        public bool IsSuccess { get; }
+
+        /// <summary>パース結果</summary>
+        public T Result =>
+            this.IsSuccess ? _result : throw new Exception($"Parse error: {Reason}");
+
+        private readonly T _result;
+
+        // 失敗した理由
+        public string Reason { get; }
+
+        internal ParseResult(Source source, bool isSuccess, T result, string reason)
+        {
+            this.Source = source;
+            this.IsSuccess = isSuccess;
+            _result = result;
+            this.Reason = reason;
+        }
+    }
+}

src/ParserCombinator/ParseResultHelper.cs

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+namespace ParserCombinator
+{
+    public static class ParseResultHelper
+    {
+        public static ParseResult<T> Success<T>(Source source, T result)
+            => new ParseResult<T>(source, true, result, default);
+
+        public static ParseResult<T> Failed<T>(Source source, string reason)
+            => new ParseResult<T>(source, false, default, reason);
+    }
+}

src/ParserCombinator/Parser.cs

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+namespace ParserCombinator
+{
+    public delegate ParseResult<T> Parser<T>(Source source);
+}

src/ParserCombinator/ParserCombinator.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <LangVersion>latest</LangVersion>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="System.Collections.Immutable" Version="1.4.0" />
+  </ItemGroup>
+</Project>