extended recover tests

README.md

@@ -69,9 +69,9 @@ Result<T> Bar()
 ```csharp
 Result<int> result = GetResult();
 
-var value = result
-    .Append("new")
-    .Map((i, s) => $"{s} result {i}")
+string value = result
+    .Append("new") // -> Result<(int, string)>
+    .Map((i, s) => $"{s} result {i}") // -> Result<string>
     .Match(
         onSuccess: x => x,
         onFailure: err => err.ToString()
@@ -81,6 +81,17 @@ var value = result
 Result<int> GetResult() => Result.Success(1);
 ```
 
+#### Recover from failure
+
+```csharp
+Result<string> failed = new NotImplementedException();
+
+Result<string> result = failed.TryRecover(err => err.Type == "System.NotImplementedException"
+    ? "recovered"
+    : err);
+// result with value: "recovered"
+```
+
 ### Try
 
 ```csharp
@@ -99,9 +110,9 @@ int SomeFunction() => 1;
 ### Ensure
 
 ```csharp
-var value = GetValue();
-Result<int> result = Ensure.That(value)
-    .NotNull()
+int? value = GetValue();
+Result<int> result = Ensure.That(value) // -> Ensure<int?>
+    .NotNull() // -> Ensure<int>
     .Satisfies(i => i < 100)
     .Result();
 

Railway.SourceGenerator/EnsureExtensionsExecutor.cs

@@ -41,22 +41,46 @@ public sealed class EnsureExtensionsExecutor : IGeneratorExecutor
 
         var sb = new StringBuilder();
 
-        sb.AppendLine($"#region Satisfies");
+        sb.AppendLine("#region Satisfies");
         errorGenerationDefinitions.ForEach(def => GenerateSatisfiesExtensions(sb, def.ErrorParameterDecl, def.ErrorValueExpr));
         sb.AppendLine("#endregion");
 
-        sb.AppendLine($"#region NotNull");
+        sb.AppendLine("#region NotNull");
         errorGenerationDefinitions.ForEach(def => GenerateNotNullExtensions(sb, def.ErrorParameterDecl, def.ErrorValueExpr));
         sb.AppendLine("#endregion");
 
-        sb.AppendLine($"#region NotEmpty");
+        sb.AppendLine("#region NotEmpty");
         errorGenerationDefinitions.ForEach(def => GenerateNotEmptyExtensions(sb, def.ErrorParameterDecl, def.ErrorValueExpr));
         sb.AppendLine("#endregion");
 
+        sb.AppendLine("#region NotWhitespace");
+        errorGenerationDefinitions.ForEach(def => GenerateNotWhitespaceExtensions(sb, def.ErrorParameterDecl, def.ErrorValueExpr));
+        sb.AppendLine("#endregion");
 
         return sb.ToString();
     }
 
+    private void GenerateNotWhitespaceExtensions(StringBuilder sb, string errorParameterDecl, string errorValueExpr)
+    {
+        string defaultErrorExpr = "?? Error.New(DefaultErrorType, $\"Value {{{ensure.ValueExpression}}} is empty or consists exclusively of white-space characters.\")";
+
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(EnsureExtensionsExecutor)}}", "1.0.0.0")]
+        public static Ensure<string> NotWhitespace(this in Ensure<string> ensure, {{errorParameterDecl}})
+        {
+            return ensure.State switch
+            {
+                ResultState.Success => string.IsNullOrWhiteSpace(ensure.Value)
+                    ? new({{errorValueExpr}} {{defaultErrorExpr}}, ensure.ValueExpression)
+                    : new(ensure.Value!, ensure.ValueExpression),
+                ResultState.Error => new(ensure.Error!, ensure.ValueExpression),
+                _ => throw new EnsureNotInitializedException(nameof(ensure))
+            };
+        }
+        """);
+    }
+
     private void GenerateNotEmptyExtensions(StringBuilder sb, string errorParameterDecl, string errorValueExpr)
     {
         string defaultErrorExpr = "?? Error.New(DefaultErrorType, $\"Value {{{ensure.ValueExpression}}} is empty.\")";

Railway.SourceGenerator/ExtensionsMethodGenerator.cs

@@ -17,6 +17,7 @@ public class ExtensionsMethodGenerator : IIncrementalGenerator
         new ResultMapExecutor(),
         new ResultBindExecutor(),
         new ResultTapExecutor(),
+        new ResultTryRecoverExecutor(),
         new ResultAppendExecutor(),
         new TryExtensionsExecutor(),
         new EnsureExtensionsExecutor(),

Railway.SourceGenerator/ResultTryRecoverExecutor.cs

@@ -0,0 +1,86 @@
+using System.Collections.Immutable;
+using System.Linq;
+using System.Text;
+using Microsoft.CodeAnalysis;
+
+namespace Just.Railway.SourceGen;
+
+internal sealed class ResultTryRecoverExecutor : ResultExtensionsExecutor
+{
+    protected override string ExtensionType => "TryRecover";
+    protected override void GenerateMethodsForArgCount(StringBuilder sb, int argCount)
+    {
+        if (argCount > 1) return;
+        
+        var templateArgNames = Enumerable.Repeat("T", argCount)
+            .ToImmutableArray();
+
+        string methodTemplateDecl = GenerateTemplateDecl(templateArgNames);
+        string resultTypeDef = GenerateResultTypeDef(templateArgNames);
+
+        sb.AppendLine($"#region {resultTypeDef}");
+
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(ResultTryRecoverExecutor)}}", "1.0.0.0")]
+        public static {{resultTypeDef}} TryRecover{{methodTemplateDecl}}(this in {{resultTypeDef}} result, Func<Error, {{resultTypeDef}}> recover)
+        {
+            return result.State switch
+            {
+                ResultState.Success => ({{resultTypeDef}})result.Value,
+                ResultState.Error => recover(result.Error!),
+                _ => throw new ResultNotInitializedException(nameof(result))
+            };
+        }
+        """);
+
+        GenerateAsyncMethods("Task", sb, templateArgNames, resultTypeDef, methodTemplateDecl);
+        GenerateAsyncMethods("ValueTask", sb, templateArgNames, resultTypeDef, methodTemplateDecl);
+
+        sb.AppendLine("#endregion");
+    }
+    private static void GenerateAsyncMethods(string taskType, StringBuilder sb, ImmutableArray<string> templateArgNames, string resultTypeDef, string methodTemplateDecl)
+    {
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(ResultTryRecoverExecutor)}}", "1.0.0.0")]
+        public static async {{taskType}}<{{resultTypeDef}}> TryRecover{{methodTemplateDecl}}(this {{taskType}}<{{resultTypeDef}}> resultTask, Func<Error, {{resultTypeDef}}> recover)
+        {
+            var result = await resultTask.ConfigureAwait(false);
+            return result.State switch
+            {
+                ResultState.Success => ({{resultTypeDef}})result.Value,
+                ResultState.Error => recover(result.Error!),
+                _ => throw new ResultNotInitializedException(nameof(resultTask))
+            };
+        }
+        """);
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(ResultTryRecoverExecutor)}}", "1.0.0.0")]
+        public static async {{taskType}}<{{resultTypeDef}}> TryRecover{{methodTemplateDecl}}(this {{resultTypeDef}} result, Func<Error, {{taskType}}<{{resultTypeDef}}>> recover)
+        {
+            return result.State switch
+            {
+                ResultState.Success => ({{resultTypeDef}})result.Value,
+                ResultState.Error => await recover(result.Error!).ConfigureAwait(false),
+                _ => throw new ResultNotInitializedException(nameof(result))
+            };
+        }
+        """);
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(ResultTryRecoverExecutor)}}", "1.0.0.0")]
+        public static async {{taskType}}<{{resultTypeDef}}> TryRecover{{methodTemplateDecl}}(this {{taskType}}<{{resultTypeDef}}> resultTask, Func<Error, {{taskType}}<{{resultTypeDef}}>> recover)
+        {
+            var result = await resultTask.ConfigureAwait(false);
+            return result.State switch
+            {
+                ResultState.Success => ({{resultTypeDef}})result.Value,
+                ResultState.Error => await recover(result.Error!).ConfigureAwait(false),
+                _ => throw new ResultNotInitializedException(nameof(resultTask))
+            };
+        }
+        """);
+    }
+}

Railway/Ensure.cs

@@ -34,18 +34,6 @@ public static partial class Ensure
             _ => throw new EnsureNotInitializedException(nameof(ensureTask))
         };
     }
-
-    [Pure] public static Ensure<string> NotWhitespace(this in Ensure<string> ensure, Error error = default!)
-    {
-        return ensure.State switch
-        {
-            ResultState.Success => string.IsNullOrWhiteSpace(ensure.Value)
-                ? new(error ?? Error.New(DefaultErrorType, $"Value {{{ensure.ValueExpression}}} is empty or consists exclusively of white-space characters."), ensure.ValueExpression)
-                : new(ensure.Value, ensure.ValueExpression),
-            ResultState.Error => new(ensure.Error!, ensure.ValueExpression),
-            _ => throw new EnsureNotInitializedException(nameof(ensure))
-        };
-    }
 }
 
 public readonly struct Ensure<T>
@@ -60,6 +48,7 @@ public readonly struct Ensure<T>
         Value = value;
         ValueExpression = valueExpression;
         State = ResultState.Success;
+        Error = default;
     }
 
     internal Ensure(Error error, string valueExpression)
@@ -72,7 +61,12 @@ public readonly struct Ensure<T>
 }
 
 [Serializable]
-public class EnsureNotInitializedException(string variableName = "this") : InvalidOperationException("Ensure was not properly initialized.")
+public class EnsureNotInitializedException : InvalidOperationException
 {
-    public string VariableName { get; } = variableName;
+    public EnsureNotInitializedException(string variableName = "this")
+        : base("Ensure was not properly initialized.")
+    {
+        VariableName = variableName;
+    }
+    public string VariableName { get; }
 }

Railway/Error.cs

@@ -52,7 +52,7 @@ public abstract class Error : IEquatable<Error>, IComparable<Error>
     [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static Error Many(Error error1, Error error2) => (error1, error2) switch
     {
-        (null, null) => new ManyErrors([]),
+        (null, null) => new ManyErrors(new List<Error>()),
         (Error err, null) => err,
         (Error err, { IsEmpty: true }) => err,
         (null, Error err) => err,
@@ -178,14 +178,17 @@ public sealed class ExceptionalError : Error
 {
     internal readonly Exception? Exception;
 
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    internal static string ToErrorType(Type exceptionType) => exceptionType.FullName ?? exceptionType.Name;
+
     internal ExceptionalError(Exception exception)
-        : this(exception.GetType().FullName ?? exception.GetType().Name, exception.Message)
+        : this(ToErrorType(exception.GetType()), exception.Message)
     {
         Exception = exception;
         ExtensionData = ExtractExtensionData(exception);
     }
     internal ExceptionalError(string message, Exception exception)
-        : this(exception.GetType().FullName ?? exception.GetType().Name, message)
+        : this(ToErrorType(exception.GetType()), message)
     {
         Exception = exception;
         ExtensionData = ExtractExtensionData(exception);
@@ -231,7 +234,7 @@ public sealed class ExceptionalError : Error
             var valueString = value.ToString();
             if (string.IsNullOrEmpty(keyString) || string.IsNullOrEmpty(valueString)) continue;
 
-            values ??= [];
+            values ??= new List<KeyValuePair<string, string>>(4);
             values.Add(new(keyString, valueString));
         }
         return values?.ToImmutableDictionary() ?? ImmutableDictionary<string, string>.Empty;
@@ -377,7 +380,11 @@ public sealed class ManyErrors : Error, IEnumerable<Error>, IReadOnlyList<Error>
 }
 
 [Serializable]
-public sealed class ErrorException(string type, string message) : Exception(message)
+public sealed class ErrorException : Exception
 {
-    public string Type { get; } = type ?? nameof(ErrorException);
+    public ErrorException(string type, string message) : base(message)
+    {
+        Type = type ?? nameof(ErrorException);
+    }
+    public string Type { get; }
 }

Railway/ErrorJsonConverter.cs

@@ -35,7 +35,7 @@ public sealed class ErrorJsonConverter : JsonConverter<Error>
 
     internal static ManyErrors ReadMany(ref Utf8JsonReader reader)
     {
-        List<Error> errors = [];
+        List<Error> errors = new(4);
         while (reader.Read())
         {
             if (reader.TokenType == JsonTokenType.StartObject)
@@ -83,7 +83,7 @@ public sealed class ErrorJsonConverter : JsonConverter<Error>
                     }
                     else if (!string.IsNullOrEmpty(propname))
                     {
-                        extensionData ??= [];
+                        extensionData ??= new(4);
                         extensionData.Add(new(propname, propvalue));
                     }
 

Railway/Railway.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFrameworks>net6.0;net7.0;net8.0</TargetFrameworks>
+    <LangVersion>10.0</LangVersion>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <AssemblyName>Just.Railway</AssemblyName>
@@ -13,7 +14,6 @@
     <Copyright>Copyright (c) 2023 JustFixMe</Copyright>
     <PackageLicenseFile>LICENSE</PackageLicenseFile>
     <PackageReadmeFile>README.md</PackageReadmeFile>
-
     <RepositoryUrl>https://github.com/JustFixMe/Just.Railway/</RepositoryUrl>
     
     <EmitCompilerGeneratedFiles Condition="'$(Configuration)'=='Debug'">true</EmitCompilerGeneratedFiles>

Railway/ReflectionHelper.cs

@@ -10,58 +10,58 @@ internal static class ReflectionHelper
 
     [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static int Compare<T>(T? left, T? right) => TypeReflectionCache<T>.CompareFunc(left, right);
-}
 
-file static class TypeReflectionCache<T>
-{
-    public static readonly Func<T?, T?, bool> IsEqualFunc;
-    public static readonly Func<T?, T?, int> CompareFunc;
-
-    static TypeReflectionCache()
+    private static class TypeReflectionCache<T>
     {
-        var type = typeof(T);
-        var isNullableStruct = type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>);
-        var underlyingType = isNullableStruct ? type.GenericTypeArguments.First() : type;
-        var thisType = typeof(TypeReflectionCache<T>);
+        public static readonly Func<T?, T?, bool> IsEqualFunc;
+        public static readonly Func<T?, T?, int> CompareFunc;
 
-        var equatableType = typeof(IEquatable<>).MakeGenericType(underlyingType);
-        if (equatableType.IsAssignableFrom(underlyingType))
+        static TypeReflectionCache()
         {
-            var isEqualFunc = thisType.GetMethod(isNullableStruct ? nameof(IsEqualNullable) : nameof(IsEqual), BindingFlags.Static | BindingFlags.Public)
-                !.MakeGenericMethod(underlyingType);
+            var type = typeof(T);
+            var isNullableStruct = type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>);
+            var underlyingType = isNullableStruct ? type.GenericTypeArguments.First() : type;
+            var thisType = typeof(TypeReflectionCache<T>);
 
-            IsEqualFunc = (Func<T?, T?, bool>)Delegate.CreateDelegate(typeof(Func<T?, T?, bool>), isEqualFunc);
-        }
-        else
-        {
-            IsEqualFunc = static (left, right) => left is null ? right is null : left.Equals(right);
+            var equatableType = typeof(IEquatable<>).MakeGenericType(underlyingType);
+            if (equatableType.IsAssignableFrom(underlyingType))
+            {
+                var isEqualFunc = thisType.GetMethod(isNullableStruct ? nameof(IsEqualNullable) : nameof(IsEqual), BindingFlags.Static | BindingFlags.Public)
+                    !.MakeGenericMethod(underlyingType);
+
+                IsEqualFunc = (Func<T?, T?, bool>)Delegate.CreateDelegate(typeof(Func<T?, T?, bool>), isEqualFunc);
+            }
+            else
+            {
+                IsEqualFunc = static (left, right) => left is null ? right is null : left.Equals(right);
+            }
+
+            var comparableType = typeof(IComparable<>).MakeGenericType(underlyingType);
+            if (comparableType.IsAssignableFrom(underlyingType))
+            {
+                var compareFunc = thisType.GetMethod(isNullableStruct ? nameof(CompareNullable) : nameof(Compare), BindingFlags.Static | BindingFlags.Public)
+                    !.MakeGenericMethod(underlyingType);
+
+                CompareFunc = (Func<T?, T?, int>)Delegate.CreateDelegate(typeof(Func<T?, T?, int>), compareFunc);
+            }
+            else
+            {
+                CompareFunc = static (left, right) => left is null
+                    ? right is null ? 0 : -1
+                    : right is null ? 1 : left.GetHashCode().CompareTo(right.GetHashCode());
+            }
         }
 
-        var comparableType = typeof(IComparable<>).MakeGenericType(underlyingType);
-        if (comparableType.IsAssignableFrom(underlyingType))
-        {
-            var compareFunc = thisType.GetMethod(isNullableStruct ? nameof(CompareNullable) : nameof(Compare), BindingFlags.Static | BindingFlags.Public)
-                !.MakeGenericMethod(underlyingType);
+    #pragma warning disable CS8604 // Possible null reference argument.
+        [Pure] public static bool IsEqual<R>(R? left, R? right) where R : notnull, IEquatable<R>, T => left is null ? right is null : left.Equals(right);
+        [Pure] public static bool IsEqualNullable<R>(R? left, R? right) where R : struct, IEquatable<R> => left is null ? right is null : right is not null && left.Value.Equals(right.Value);
 
-            CompareFunc = (Func<T?, T?, int>)Delegate.CreateDelegate(typeof(Func<T?, T?, int>), compareFunc);
-        }
-        else
-        {
-            CompareFunc = static (left, right) => left is null
-                ? right is null ? 0 : -1
-                : right is null ? 1 : left.GetHashCode().CompareTo(right.GetHashCode());
-        }
+        [Pure] public static int Compare<R>(R? left, R? right) where R : notnull, IComparable<R>, T => left is null
+            ? right is null ? 0 : -1
+            : right is null ? 1 : left.CompareTo(right);
+        [Pure] public static int CompareNullable<R>(R? left, R? right) where R : struct, IComparable<R> => left is null
+            ? right is null ? 0 : -1
+            : right is null ? 1 : left.Value.CompareTo(right.Value);
+    #pragma warning restore CS8604 // Possible null reference argument.
     }
-
-#pragma warning disable CS8604 // Possible null reference argument.
-    [Pure] public static bool IsEqual<R>(R? left, R? right) where R : notnull, IEquatable<R>, T => left is null ? right is null : left.Equals(right);
-    [Pure] public static bool IsEqualNullable<R>(R? left, R? right) where R : struct, IEquatable<R> => left is null ? right is null : right is not null && left.Value.Equals(right.Value);
-
-    [Pure] public static int Compare<R>(R? left, R? right) where R : notnull, IComparable<R>, T => left is null
-        ? right is null ? 0 : -1
-        : right is null ? 1 : left.CompareTo(right);
-    [Pure] public static int CompareNullable<R>(R? left, R? right) where R : struct, IComparable<R> => left is null
-        ? right is null ? 0 : -1
-        : right is null ? 1 : left.Value.CompareTo(right.Value);
-#pragma warning restore CS8604 // Possible null reference argument.
 }

Railway/Result.cs

@@ -8,6 +8,7 @@ internal enum ResultState : byte
 
 public readonly partial struct Result : IEquatable<Result>
 {
+    internal SuccessUnit Value => new();
     internal readonly Error? Error;
     internal readonly ResultState State;
 
@@ -51,12 +52,17 @@ public readonly partial struct Result : IEquatable<Result>
     [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static implicit operator Result(Error error) => new(error ?? throw new ArgumentNullException(nameof(error)));
     [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static implicit operator Result(Exception exception) => new(
+        new ExceptionalError(exception ?? throw new ArgumentNullException(nameof(exception))));
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static implicit operator Result<SuccessUnit>(Result result) => result.State switch
     {
         ResultState.Success => new(new SuccessUnit()),
         ResultState.Error => new(result.Error!),
         _ => throw new ResultNotInitializedException(nameof(result))
     };
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static explicit operator Result(SuccessUnit _) => new(null);
 
     [Pure] public bool IsSuccess => Error is null;
     [Pure] public bool IsFailure => Error is not null;
@@ -136,16 +142,23 @@ public readonly struct Result<T> : IEquatable<Result<T>>
     {
         Value = value;
         State = ResultState.Success;
+        Error = default;
     }
 
-    [Pure] public static explicit operator Result(Result<T> result) => result.State switch
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static explicit operator Result(Result<T> result) => result.State switch
     {
         ResultState.Success => new(null),
         ResultState.Error => new(result.Error!),
         _ => throw new ResultNotInitializedException(nameof(result))
     };
-    [Pure] public static implicit operator Result<T>(Error error) => new(error);
-    [Pure] public static implicit operator Result<T>(T value) => new(value);
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static implicit operator Result<T>(Error error) => new(error);
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static implicit operator Result<T>(Exception exception) => new(
+        new ExceptionalError(exception ?? throw new ArgumentNullException(nameof(exception))));
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static implicit operator Result<T>(T value) => new(value);
     [Pure] public bool IsSuccess => State == ResultState.Success;
     [Pure] public bool IsFailure => State == ResultState.Error;
 
@@ -263,7 +276,12 @@ public readonly struct SuccessUnit : IEquatable<SuccessUnit>
 }
 
 [Serializable]
-public class ResultNotInitializedException(string variableName = "this") : InvalidOperationException("Result was not properly initialized.")
+public class ResultNotInitializedException : InvalidOperationException
 {
-    public string VariableName { get; } = variableName;
+    public ResultNotInitializedException(string variableName = "this")
+        : base("Result was not properly initialized.")
+    {
+        VariableName = variableName;
+    }
+    public string VariableName { get; }
 }

Railway/ResultExtensions.cs

@@ -89,7 +89,7 @@ public static partial class ResultExtensions
             {
                 case ResultState.Error:
                     hasErrors = true;
-                    errors ??= [];
+                    errors ??= new(4);
                     errors.Add(result.Error!);
                     break;
 
@@ -123,13 +123,13 @@ public static partial class ResultExtensions
             {
                 case ResultState.Error:
                     hasErrors = true;
-                    errors ??= [];
+                    errors ??= new(4);
                     errors.Add(result.Error!);
                     break;
 
                 case ResultState.Success:
                     if (hasErrors) goto afterLoop;
-                    values ??= [];
+                    values ??= new(4);
                     values.Add(result.Value);
                     break;
                     

Raliway.Tests/Results/GeneralUsage.cs

@@ -128,4 +128,45 @@ public class GeneralUsage
         // Then
         Assert.Equal("satisfied", result);
     }
+
+    [Fact]
+    public void RecoverResultFromFailureState()
+    {
+        // Given
+        Result<string> failed = new NotImplementedException();
+        // When
+        var result = failed.TryRecover(err => 
+        {
+            Assert.IsType<NotImplementedException>(err.ToException());
+
+            if (err.Type == "System.NotImplementedException")
+                return "recovered";
+
+            Assert.Fail();
+            return "";
+        });
+        // Then
+        Assert.True(result.IsSuccess);
+        Assert.Equal("recovered", result.Value);
+    }
+
+    [Fact]
+    public void WhenCanNotRecoverResultFromFailureState()
+    {
+        // Given
+        var error = Error.New("test");
+        Result<string> failed = new NotImplementedException();
+        // When
+        var result = failed.TryRecover(err =>
+        {
+            if (err.Type == "System.NotImplementedException")
+                return error;
+            
+            Assert.Fail();
+            return "";
+        });
+        // Then
+        Assert.True(result.IsFailure);
+        Assert.Equal(error, result.Error);
+    }
 }