add fp3 sample
This commit is contained in:
Oli Sturm
@@ -0,0 +1,32 @@
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using CsharpFp3.Domain;
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using CsharpFp3.Infrastructure;
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using CsharpFp3.Library;
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namespace CsharpFp3.Application;
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using CreateResultType = Result<Func<Guid, decimal, Result<Account, AccountError>>, AppError>;
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public abstract record AppError
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{
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public sealed record RepositoryCreationFailed(string Message) : AppError;
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public sealed record InnerAccountError(AccountError InnerError) : AppError;
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}
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public static class AccountApplication
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{
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public static CreateResultType CreateWithdrawMoney(Repository repo) =>
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CreateResultType.Ok(
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(accountId, amount) =>
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repo.LoadAccount(accountId)
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.Log("App load", "Account loaded")
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.Log("App exec wdrwl", $"[App] Executing withdrawal of {amount:0.00}...")
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.Bind(account => AccountDomain.Withdraw(account, new Money(amount)))
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.Log(
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"App wdrwl done",
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a => $"Withdrawal applied. New balance: {a.Balance.Amount:0.00}"
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)
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.Bind(repo.SaveAccount)
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.Log("App acc svd", "[App] Account persisted.")
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);
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}
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@@ -0,0 +1,44 @@
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using CsharpFp3.Library;
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namespace CsharpFp3.Domain;
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public sealed record Account(Guid Id, Money Balance);
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public abstract record AccountError
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{
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public sealed record OpeningBalanceMustBeNonNegative : AccountError;
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public sealed record AmountMustBePositive : AccountError;
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public sealed record InsufficientBalance(Money Balance, Money Amount) : AccountError;
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public sealed record AccountNotFound(Guid AccountId) : AccountError;
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}
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public static class AccountDomain
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{
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public static Result<Account, AccountError> Open(Guid id, Money openingBalance) =>
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openingBalance.Amount < 0m
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? Result<Account, AccountError>.Fail(new AccountError.OpeningBalanceMustBeNonNegative())
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: Result<Account, AccountError>.Ok(new Account(id, openingBalance));
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public static Result<Account, AccountError> Withdraw(Account account, Money amount) =>
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(account.Balance.Amount, amount.Amount) switch
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{
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(_, <= 0m) => Result<Account, AccountError>.Fail(
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new AccountError.AmountMustBePositive()
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),
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var (balance, transaction) when balance < transaction => Result<
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Account,
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AccountError
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>.Fail(new AccountError.InsufficientBalance(account.Balance, amount)),
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var (balance, transaction) => Result<Account, AccountError>.Ok(
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account with
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{
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Balance = new Money(balance - transaction),
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}
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),
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};
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}
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@@ -0,0 +1,3 @@
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namespace CsharpFp3.Domain;
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public sealed record Money(decimal Amount);
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@@ -0,0 +1,44 @@
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using CsharpFp3.Domain;
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using CsharpFp3.Library;
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using static CsharpFp3.Library.Logging;
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namespace CsharpFp3.Infrastructure;
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public sealed record Repository(
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Func<Guid, Result<Account, AccountError>> LoadAccount,
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Func<Account, Result<Account, AccountError>> SaveAccount
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);
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public static class InMemoryAccountRepository
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{
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public static Repository Create()
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{
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Dictionary<Guid, Account> store = new();
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Result<Account, AccountError> GetById(Guid id) =>
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store.TryGetValue(id, out var account)
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? LogReturn(
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$"[Repo] Loaded account {id}",
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Result<Account, AccountError>.Ok(account)
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)
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: LogReturn(
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$"[Repo] Account {id} not found",
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Result<Account, AccountError>.Fail(new AccountError.AccountNotFound(id))
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);
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Result<Account, AccountError> Save(Account account)
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{
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store[account.Id] = account;
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// no failure modes here
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return LogReturn(
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$"[Repo] Saved account {account.Id} with balance {account.Balance.Amount:0.00}",
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Result<Account, AccountError>.Ok(account)
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);
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}
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// What if something goes wrong?
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// throw new Exception("Something went wrong");
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return new Repository(GetById, Save);
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}
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}
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@@ -0,0 +1,21 @@
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namespace CsharpFp3.Library;
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public static class Logging
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{
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public static T LogReturn<T>(string message, T r)
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{
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Console.WriteLine(message);
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return r;
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}
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public static Action<T> Output<T>(string src, string message) =>
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x =>
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{
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Console.WriteLine($"[{src}] {message} | {x}");
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};
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public static void OutputError<T>(string src, T error)
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{
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Console.Error.WriteLine($"\e[1;31m[{src} ERROR]\e[0m {error}");
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}
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}
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@@ -0,0 +1,126 @@
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namespace CsharpFp3.Library;
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public readonly record struct Result<T, E>
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{
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private readonly T _value;
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private readonly E _error;
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public bool IsSuccess { get; }
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public bool IsFailure => !IsSuccess;
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public T Value =>
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IsSuccess
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? _value
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: throw new InvalidOperationException("No value present for failed result.");
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public E Error =>
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IsFailure
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? _error
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: throw new InvalidOperationException("No error present for successful result.");
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private Result(T value)
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{
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_value = value;
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_error = default!;
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IsSuccess = true;
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}
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private Result(E error)
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{
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_value = default!;
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_error = error;
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IsSuccess = false;
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}
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public static Result<T, E> Ok(T value) => new(value);
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public static Result<T, E> Fail(E error) => new(error);
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public TResult Match<TResult>(Func<T, TResult> onSuccess, Func<E, TResult> onFailure) =>
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IsSuccess ? onSuccess(_value) : onFailure(_error);
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public void Switch(Action<T> onSuccess, Action<E> onFailure)
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{
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if (IsSuccess)
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onSuccess(_value);
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else
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onFailure(_error);
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}
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public static Result<T, E> Catch(Func<T> f, Func<Exception, E> exceptionMapper)
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{
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try
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{
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var result = f();
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return Result<T, E>.Ok(result);
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}
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catch (Exception e)
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{
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return Result<T, E>.Fail(exceptionMapper(e));
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}
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}
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}
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public static class ResultExtensions
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{
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public static Result<TOut, E> Bind<TIn, TOut, E>(
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this Result<TIn, E> result,
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Func<TIn, Result<TOut, E>> binder
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) => result.IsSuccess ? binder(result.Value) : Result<TOut, E>.Fail(result.Error);
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public static Result<TOut, E> Map<TIn, TOut, E>(
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this Result<TIn, E> result,
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Func<TIn, TOut> mapper
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) =>
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result.IsSuccess
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? Result<TOut, E>.Ok(mapper(result.Value))
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: Result<TOut, E>.Fail(result.Error);
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public static Result<T, E> Tap<T, E>(this Result<T, E> result, Action<T> action)
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{
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if (result.IsSuccess)
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action(result.Value);
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return result;
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}
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public static Result<T, E> TapError<T, E>(this Result<T, E> result, Action<E> action)
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{
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if (result.IsFailure)
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action(result.Error);
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return result;
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}
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public static Result<T, EOut> MapError<T, EIn, EOut>(
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this Result<T, EIn> result,
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Func<EIn, EOut> map
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) =>
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result.IsSuccess
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? Result<T, EOut>.Ok(result.Value)
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: Result<T, EOut>.Fail(map(result.Error));
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public static Result<T, E> Log<T, E>(this Result<T, E> result, string src, string msg) =>
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Tap(result, Logging.Output<T>(src, msg)).TapError(m => Logging.OutputError(src, m));
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public static Result<T, E> Log<T, E>(
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this Result<T, E> result,
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string src,
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Func<T, string> renderText
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) =>
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Tap(result, x => Logging.Output<T>(src, renderText(x))(x))
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.TapError(m => Logging.OutputError(src, m));
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public static Result<TOut, E> Select<TIn, TOut, E>(
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this Result<TIn, E> result,
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Func<TIn, TOut> mapper
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) => result.Map(mapper);
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public static Result<TOut, E> SelectMany<TIn, TIntermediate, TOut, E>(
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this Result<TIn, E> result,
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Func<TIn, Result<TIntermediate, E>> binder,
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Func<TIn, TIntermediate, TOut> projector
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) => result.Bind(x => binder(x).Map(y => projector(x, y)));
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}
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@@ -0,0 +1,41 @@
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using CsharpFp3.Application;
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using CsharpFp3.Domain;
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using CsharpFp3.Infrastructure;
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using CsharpFp3.Library;
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Console.WriteLine("[csharp-fp3] Starting withdraw money demo...");
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var accountId = Guid.NewGuid();
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// try changing this to 250m to see an error being handled
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var withdrawalAmount = 100m;
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Result<Repository, AppError>
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.Catch(
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InMemoryAccountRepository.Create,
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ex => new AppError.RepositoryCreationFailed(ex.Message)
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)
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.Bind(repo =>
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AccountApplication
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.CreateWithdrawMoney(repo)
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.Bind(withdrawMoney =>
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AccountDomain
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.Open(accountId, new Money(200m))
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.Log(
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"csharp-fp3 seed",
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account =>
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$"Seeding account {account.Id} with opening balance {account.Balance}"
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)
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.Bind(repo.SaveAccount)
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.Log(
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"csharp-fp3 exec",
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$"Executing withdrawal {withdrawalAmount:0.00} from account {accountId}"
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)
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.Bind<Account, Account, AccountError>(account =>
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withdrawMoney(account.Id, withdrawalAmount)
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)
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.Log("csharp-fp3 new balance", account => $"New balance is {account.Balance}")
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.MapError(ae => (AppError)new AppError.InnerAccountError(ae))
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)
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)
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.Log("csharp-fp3 done", "Demo completed.");
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@@ -0,0 +1,9 @@
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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net10.0</TargetFramework>
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<RootNamespace>CsharpFp3</RootNamespace>
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<ImplicitUsings>enable</ImplicitUsings>
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<Nullable>enable</Nullable>
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</PropertyGroup>
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</Project>
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