Building Objects

When building complex objects where each field depends on successful computation, the do/bind pattern provides an elegant solution. It lets you accumulate successful results into a growing object.

What is `do`?

do creates a starting point—a Success with an empty object:

import { import ResultResult } from '@praha/byethrow';

const const start: Result.Result<{}, never>start = import ResultResult.function do(): Result.Result<{}, never>
export do
Alias for succeed({}). Commonly used as a neutral base value in functional chains or monadic pipelines.
@function@exampleimport { Result } from '@praha/byethrow';

const result = Result.do();
// Result.Result<{}, never>
@categoryCreatorsdo();
// { type: 'Success', value: {} }

What is `bind`?

bind adds a new field to the accumulated object. It:

Receives the current accumulated object
Runs a computation that returns a Result
If successful, merges the result into the object under the given key
If failed, short-circuits and returns the failure

import { import ResultResult } from '@praha/byethrow';

const const result: Result.Result<{
    name: "Alice";
    age: 30;
}, never>
result = import ResultResult.const pipe: <Result.Result<{}, never>, Result.Result<{
    name: "Alice";
}, never>, Result.Result<{
    name: "Alice";
    age: 30;
}, never>>(a: Result.Result<{}, never>, ab: (a: Result.Result<{}, never>) => Result.Result<{
    name: "Alice";
}, never>, bc: (b: Result.Result<{
    name: "Alice";
}, never>) => Result.Result<{
    name: "Alice";
    age: 30;
}, never>) => Result.Result<{
    name: "Alice";
    age: 30;
}, never> (+25 overloads)
pipe(
  import ResultResult.function do(): Result.Result<{}, never>
export do
Alias for succeed({}). Commonly used as a neutral base value in functional chains or monadic pipelines.
@function@exampleimport { Result } from '@praha/byethrow';

const result = Result.do();
// Result.Result<{}, never>
@categoryCreatorsdo(),
  import ResultResult.const bind: <"name", Result.Result<{}, never>, Result.Result<"Alice", never>>(name: "name", fn: (a: {}) => Result.Result<"Alice", never>) => (result: Result.Result<{}, never>) => Result.Result<{
    name: "Alice";
}, never> (+1 overload)
bind('name', () => import ResultResult.const succeed: <"Alice">(value: "Alice") => Result.Result<"Alice", never> (+1 overload)succeed('Alice')),
  import ResultResult.const bind: <"age", Result.Result<{
    name: "Alice";
}, never>, Result.Result<30, never>>(name: "age", fn: (a: {
    name: "Alice";
}) => Result.Result<30, never>) => (result: Result.Result<{
    name: "Alice";
}, never>) => Result.Result<{
    name: "Alice";
    age: 30;
}, never> (+1 overload)
bind('age', () => import ResultResult.const succeed: <30>(value: 30) => Result.Result<30, never> (+1 overload)succeed(30)),
);
// { type: 'Success', value: { name: 'Alice', age: 30 } }

Using Previous Values

The power of bind is that each step can access previous values:

import { import ResultResult } from '@praha/byethrow';

const const result: Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
    profile: {
        bio: string;
    };
}, "UserNotFound" | "ProfileNotFound">
result = import ResultResult.const pipe: <Result.Result<{}, never>, Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
}, "UserNotFound">, Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
    profile: {
        bio: string;
    };
}, "UserNotFound" | "ProfileNotFound">>(a: Result.Result<{}, never>, ab: (a: Result.Result<{}, never>) => Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
}, "UserNotFound">, bc: (b: Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
}, "UserNotFound">) => Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
    profile: {
        bio: string;
    };
}, "UserNotFound" | "ProfileNotFound">) => Result.ResultAsync<...> (+25 overloads)
pipe(
  import ResultResult.function do(): Result.Result<{}, never>
export do
Alias for succeed({}). Commonly used as a neutral base value in functional chains or monadic pipelines.
@function@exampleimport { Result } from '@praha/byethrow';

const result = Result.do();
// Result.Result<{}, never>
@categoryCreatorsdo(),
  import ResultResult.const bind: <"user", Result.Result<{}, never>, Result.ResultAsync<{
    id: string;
    profileId: string;
}, "UserNotFound">>(name: "user", fn: (a: {}) => Result.ResultAsync<{
    id: string;
    profileId: string;
}, "UserNotFound">) => (result: Result.Result<{}, never>) => Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
}, "UserNotFound"> (+1 overload)
bind('user', () => const fetchUser: (userId: string) => Result.ResultAsync<{
    id: string;
    profileId: string;
}, "UserNotFound">
fetchUser('user-123')),
  import ResultResult.const bind: <"profile", Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
}, "UserNotFound">, Result.ResultAsync<{
    bio: string;
}, "ProfileNotFound">>(name: "profile", fn: (a: {
    user: {
        id: string;
        profileId: string;
    };
}) => Result.ResultAsync<{
    bio: string;
}, "ProfileNotFound">) => (result: Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
}, "UserNotFound">) => Result.ResultAsync<{
    user: {
        id: string;
        profileId: string;
    };
    profile: {
        bio: string;
    };
}, "UserNotFound" | "ProfileNotFound"> (+1 overload)
bind('profile', ({ user: {
    id: string;
    profileId: string;
}
user }) => const fetchProfile: (profileId: string) => Result.ResultAsync<{
    bio: string;
}, "ProfileNotFound">
fetchProfile(user: {
    id: string;
    profileId: string;
}
user.profileId: stringprofileId)), // Uses user!
);

Failure Short-Circuits

If any bind fails, subsequent binds are skipped:

import { import ResultResult } from '@praha/byethrow';

const const result: Result.Result<{
    a: 1;
    b: never;
    c: 3;
    d: 4;
}, "Error!">
result = import ResultResult.const pipe: <Result.Result<{}, never>, Result.Result<{
    a: 1;
}, never>, Result.Result<{
    a: 1;
    b: never;
}, "Error!">, Result.Result<{
    a: 1;
    b: never;
    c: 3;
}, "Error!">, Result.Result<{
    a: 1;
    b: never;
    c: 3;
    d: 4;
}, "Error!">>(a: Result.Result<{}, never>, ab: (a: Result.Result<{}, never>) => Result.Result<{
    a: 1;
}, never>, bc: (b: Result.Result<{
    a: 1;
}, never>) => Result.Result<{
    a: 1;
    b: never;
}, "Error!">, cd: (c: Result.Result<{
    a: 1;
    b: never;
}, "Error!">) => Result.Result<{
    a: 1;
    b: never;
    c: 3;
}, "Error!">, de: (d: Result.Result<...>) => Result.Result<...>) => Result.Result<...> (+25 overloads)
pipe(
  import ResultResult.function do(): Result.Result<{}, never>
export do
Alias for succeed({}). Commonly used as a neutral base value in functional chains or monadic pipelines.
@function@exampleimport { Result } from '@praha/byethrow';

const result = Result.do();
// Result.Result<{}, never>
@categoryCreatorsdo(),
  import ResultResult.const bind: <"a", Result.Result<{}, never>, Result.Result<1, never>>(name: "a", fn: (a: {}) => Result.Result<1, never>) => (result: Result.Result<{}, never>) => Result.Result<{
    a: 1;
}, never> (+1 overload)
bind('a', () => import ResultResult.const succeed: <1>(value: 1) => Result.Result<1, never> (+1 overload)succeed(1)),
  import ResultResult.const bind: <"b", Result.Result<{
    a: 1;
}, never>, Result.Result<never, "Error!">>(name: "b", fn: (a: {
    a: 1;
}) => Result.Result<never, "Error!">) => (result: Result.Result<{
    a: 1;
}, never>) => Result.Result<{
    a: 1;
    b: never;
}, "Error!"> (+1 overload)
bind('b', () => import ResultResult.const fail: <"Error!">(error: "Error!") => Result.Result<never, "Error!"> (+1 overload)fail('Error!')),  // Fails here
  import ResultResult.const bind: <"c", Result.Result<{
    a: 1;
    b: never;
}, "Error!">, Result.Result<3, never>>(name: "c", fn: (a: {
    a: 1;
    b: never;
}) => Result.Result<3, never>) => (result: Result.Result<{
    a: 1;
    b: never;
}, "Error!">) => Result.Result<{
    a: 1;
    b: never;
    c: 3;
}, "Error!"> (+1 overload)
bind('c', () => import ResultResult.const succeed: <3>(value: 3) => Result.Result<3, never> (+1 overload)succeed(3)),      // Skipped
  import ResultResult.const bind: <"d", Result.Result<{
    a: 1;
    b: never;
    c: 3;
}, "Error!">, Result.Result<4, never>>(name: "d", fn: (a: {
    a: 1;
    b: never;
    c: 3;
}) => Result.Result<4, never>) => (result: Result.Result<{
    a: 1;
    b: never;
    c: 3;
}, "Error!">) => Result.Result<{
    a: 1;
    b: never;
    c: 3;
    d: 4;
}, "Error!"> (+1 overload)
bind('d', () => import ResultResult.const succeed: <4>(value: 4) => Result.Result<4, never> (+1 overload)succeed(4)),      // Skipped
);
// { type: 'Failure', error: 'Error!' }

When you need to fetch multiple related resources and combine them:

import { import ResultResult } from '@praha/byethrow';

type type OrderDetails = {
    orderId: string;
    customerName: string;
    products: {
        id: string;
        name: string;
        price: number;
    }[];
    totalPrice: number;
}
OrderDetails = {
  orderId: stringorderId: string;
  customerName: stringcustomerName: string;
  products: {
    id: string;
    name: string;
    price: number;
}[]
products: { id: stringid: string; name: stringname: string; price: numberprice: number }[];
  totalPrice: numbertotalPrice: number;
};

const const getOrderDetails: (orderId: string) => Result.ResultAsync<OrderDetails, "OrderNotFound" | "UserNotFound" | "ProductNotFound">getOrderDetails = (orderId: stringorderId: string): import ResultResult.type ResultAsync<T, E> = Promise<Result.Result<T, E>>An asynchronous variant of
Result
, wrapped in a Promise.
@typeParamT  - The type of the Success value.@typeParamE  - The type of the Failure value.@exampleimport { Result } from '@praha/byethrow';

const fetchData = async (): Result.ResultAsync<string, Error> => {
  try {
    const data = await fetch('...');
    return { type: 'Success', value: await data.text() };
  } catch (err) {
    return { type: 'Failure', error: err as Error };
  }
};
@categoryCore  TypesResultAsync<type OrderDetails = {
    orderId: string;
    customerName: string;
    products: {
        id: string;
        name: string;
        price: number;
    }[];
    totalPrice: number;
}
OrderDetails, 'OrderNotFound' | 'UserNotFound' | 'ProductNotFound'> => {
  return import ResultResult.const pipe: <Result.Result<{}, never>, Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
}, "OrderNotFound">, Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
    user: {
        id: string;
        name: string;
    };
}, "OrderNotFound" | "UserNotFound">, Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
    user: {
        id: string;
        name: string;
    };
    products: {
        id: string;
        name: string;
        price: number;
    }[];
}, "OrderNotFound" | "UserNotFound" | "ProductNotFound">, Result.ResultAsync<{
    readonly orderId: string;
    readonly customerName: string;
    readonly products: {
        id: string;
        name: string;
        price: number;
    }[];
    readonly totalPrice: number;
}, "OrderNotFound" | ... 1 more ... | "ProductNotFound">>(a: Result.Result<...>, ab: (a: Result.Result<...>) => Result.ResultAsync<...>, bc: (b: Result.ResultAsync<...>) => Result.ResultAsync<...>, cd: (c: Result.ResultAsync<...>) => Result.ResultAsync<...>, de: (d: Result.ResultAsync<...>) => Result.ResultAsync<...>) => Result.ResultAsync<...> (+25 overloads)
pipe(
    import ResultResult.function do(): Result.Result<{}, never>
export do
Alias for succeed({}). Commonly used as a neutral base value in functional chains or monadic pipelines.
@function@exampleimport { Result } from '@praha/byethrow';

const result = Result.do();
// Result.Result<{}, never>
@categoryCreatorsdo(),
    import ResultResult.const bind: <"order", Result.Result<{}, never>, Result.ResultAsync<{
    id: string;
    userId: string;
    productIds: string[];
}, "OrderNotFound">>(name: "order", fn: (a: {}) => Result.ResultAsync<{
    id: string;
    userId: string;
    productIds: string[];
}, "OrderNotFound">) => (result: Result.Result<{}, never>) => Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
}, "OrderNotFound"> (+1 overload)
bind('order', () => const fetchOrder: (orderId: string) => Result.ResultAsync<{
    id: string;
    userId: string;
    productIds: string[];
}, "OrderNotFound">
fetchOrder(orderId: stringorderId)),
    import ResultResult.const bind: <"user", Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
}, "OrderNotFound">, Result.ResultAsync<{
    id: string;
    name: string;
}, "UserNotFound">>(name: "user", fn: (a: {
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
}) => Result.ResultAsync<{
    id: string;
    name: string;
}, "UserNotFound">) => (result: Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
}, "OrderNotFound">) => Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
    user: {
        id: string;
        name: string;
    };
}, "OrderNotFound" | "UserNotFound"> (+1 overload)
bind('user', ({ order: {
    id: string;
    userId: string;
    productIds: string[];
}
order }) => const fetchUser: (userId: string) => Result.ResultAsync<{
    id: string;
    name: string;
}, "UserNotFound">
fetchUser(order: {
    id: string;
    userId: string;
    productIds: string[];
}
order.userId: stringuserId)),
    import ResultResult.const bind: <"products", Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
    user: {
        id: string;
        name: string;
    };
}, "OrderNotFound" | "UserNotFound">, Result.ResultAsync<{
    id: string;
    name: string;
    price: number;
}[], "ProductNotFound">>(name: "products", fn: (a: {
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
    user: {
        id: string;
        name: string;
    };
}) => Result.ResultAsync<{
    id: string;
    name: string;
    price: number;
}[], "ProductNotFound">) => (result: Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
    user: {
        id: string;
        name: string;
    };
}, "OrderNotFound" | "UserNotFound">) => Result.ResultAsync<...> (+1 overload)
bind('products', ({ order: {
    id: string;
    userId: string;
    productIds: string[];
}
order }) => const fetchProducts: (productIds: string[]) => Result.ResultAsync<{
    id: string;
    name: string;
    price: number;
}[], "ProductNotFound">
fetchProducts(order: {
    id: string;
    userId: string;
    productIds: string[];
}
order.productIds: string[]productIds)),
    import ResultResult.const map: <Result.ResultAsync<{
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
    user: {
        id: string;
        name: string;
    };
    products: {
        id: string;
        name: string;
        price: number;
    }[];
}, "OrderNotFound" | "UserNotFound" | "ProductNotFound">, {
    readonly orderId: string;
    readonly customerName: string;
    readonly products: {
        id: string;
        name: string;
        price: number;
    }[];
    readonly totalPrice: number;
}>(fn: (a: {
    order: {
        id: string;
        userId: string;
        productIds: string[];
    };
    user: {
        id: string;
        name: string;
    };
    products: {
        id: string;
        name: string;
        price: number;
    }[];
}) => {
    readonly orderId: string;
    readonly customerName: string;
    readonly products: {
        id: string;
        name: string;
        price: number;
    }[];
    readonly totalPrice: number;
}) => (result: Result.ResultAsync<...>) => Result.ResultAsync<...> (+1 overload)
map(({ order: {
    id: string;
    userId: string;
    productIds: string[];
}
order, user: {
    id: string;
    name: string;
}
user, products: {
    id: string;
    name: string;
    price: number;
}[]
products }) => ({
      orderId: stringorderId: order: {
    id: string;
    userId: string;
    productIds: string[];
}
order.id: stringid,
      customerName: stringcustomerName: user: {
    id: string;
    name: string;
}
user.name: stringname,
      products: {
    id: string;
    name: string;
    price: number;
}[]
products,
      totalPrice: numbertotalPrice: products: {
    id: string;
    name: string;
    price: number;
}[]
products.Array<{ id: string; name: string; price: number; }>.reduce<number>(callbackfn: (previousValue: number, currentValue: {
    id: string;
    name: string;
    price: number;
}, currentIndex: number, array: {
    id: string;
    name: string;
    price: number;
}[]) => number, initialValue: number): number (+2 overloads)
Calls the specified callback function for all the elements in an array. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.
@paramcallbackfn  A function that accepts up to four arguments. The reduce method calls the callbackfn function one time for each element in the array.@paraminitialValue  If initialValue is specified, it is used as the initial value to start the accumulation. The first call to the callbackfn function provides this value as an argument instead of an array value.reduce((sum: numbersum, p: {
    id: string;
    name: string;
    price: number;
}
p) => sum: numbersum + p: {
    id: string;
    name: string;
    price: number;
}
p.price: numberprice, 0),
    })),
  );
};
// Uses order data to fetch user and products, then combines everything

References

Function	Purpose
do()	Start with `Success<{}>`
bind(name, fn)	Add field to accumulated object

#Building Objects

#What is do?

#What is bind?

#Using Previous Values

#Failure Short-Circuits

#Example: Fetching Related Data