Importing Result

@praha/byethrow provides two distinct import methods to balance efficient development with optimal bundle size. Both approaches fully support tree-shaking, ensuring that unused features are automatically excluded from your final bundle.

Two Import Methods

Explicit Namespace Approach (`Result`)

For verbose and explicit code that prioritizes clarity, use the Result namespace:

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

const const validateUser: (id: string) => Result.Failure<Error> | Result.Success<string>validateUser = (id: stringid: string) => {
  if (!id: stringid.String.startsWith(searchString: string, position?: number): booleanReturns true if the sequence of elements of searchString converted to a String is the
same as the corresponding elements of this object (converted to a String) starting at
position. Otherwise returns false.startsWith('u')) {
    return import ResultResult.const fail: <Error>(error: Error) => Result.Result<never, Error> (+1 overload)fail(new var Error: ErrorConstructor
new (message?: string, options?: ErrorOptions) => Error (+1 overload)
Error('Invalid ID format'));
  }
  return import ResultResult.const succeed: <string>(value: string) => Result.Result<string, never> (+1 overload)succeed(id: stringid);
};

const const result: Result.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error>
result = import ResultResult.const pipe: <Result.Result<"u123", never>, Result.Result<string, Error>, Result.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error>>(a: Result.Result<"u123", never>, ab: (a: Result.Result<"u123", never>) => Result.Result<string, Error>, bc: (b: Result.Result<string, Error>) => Result.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error>) => Result.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error> (+25 overloads)
pipe(
  import ResultResult.const succeed: <"u123">(value: "u123") => Result.Result<"u123", never> (+1 overload)succeed('u123'),
  import ResultResult.const andThen: <Result.Result<"u123", never>, Result.Failure<Error> | Result.Success<string>>(fn: (a: "u123") => Result.Failure<Error> | Result.Success<string>) => (result: Result.Result<"u123", never>) => Result.Result<string, Error> (+1 overload)andThen(const validateUser: (id: string) => Result.Failure<Error> | Result.Success<string>validateUser),
  import ResultResult.const map: <Result.Result<string, Error>, {
    readonly id: string;
    readonly name: "John Doe";
}>(fn: (a: string) => {
    readonly id: string;
    readonly name: "John Doe";
}) => (result: Result.Result<string, Error>) => Result.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error> (+1 overload)
map(id: stringid => ({ id: stringid, name: "John Doe"name: 'John Doe' }))
);

if (import ResultResult.const isSuccess: <{
    readonly id: string;
    readonly name: "John Doe";
}>(result: Result.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, unknown>) => result is Result.Success<{
    readonly id: string;
    readonly name: "John Doe";
}>
Type guard to check if a
Result
is a
Success
.
@function@typeParamT  - The type of the success value.@paramresult  - The Result to check.@returnstrue if the result is a Success, otherwise false.@exampleimport { Result } from '@praha/byethrow';

const result: Result.Result<number, string> = { type: 'Success', value: 10 };
if (Result.isSuccess(result)) {
  console.log(result.value); // Safe access to value
}
@categoryType  GuardsisSuccess(const result: Result.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error>
result)) {
  var console: ConsoleThe console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:

A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.

Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr

Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@seesourceconsole.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout

See util.format() for more information.
@sincev0 .1.100log(const result: Result.Success<{
    readonly id: string;
    readonly name: "John Doe";
}>
result.value: {
    readonly id: string;
    readonly name: "John Doe";
}
value);
}

Shorthand Alias (`R`)

For concise code that favors brevity, use the R alias:

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

const const validateUser: (id: string) => R.Failure<Error> | R.Success<string>validateUser = (id: stringid: string) => {
  if (!id: stringid.String.startsWith(searchString: string, position?: number): booleanReturns true if the sequence of elements of searchString converted to a String is the
same as the corresponding elements of this object (converted to a String) starting at
position. Otherwise returns false.startsWith('u')) {
    return import RR.const fail: <Error>(error: Error) => R.Result<never, Error> (+1 overload)fail(new var Error: ErrorConstructor
new (message?: string, options?: ErrorOptions) => Error (+1 overload)
Error('Invalid ID format'));
  }
  return import RR.const succeed: <string>(value: string) => R.Result<string, never> (+1 overload)succeed(id: stringid);
};

const const result: R.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error>
result = import RR.const pipe: <R.Result<"u123", never>, R.Result<string, Error>, R.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error>>(a: R.Result<"u123", never>, ab: (a: R.Result<"u123", never>) => R.Result<string, Error>, bc: (b: R.Result<string, Error>) => R.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error>) => R.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error> (+25 overloads)
pipe(
  import RR.const succeed: <"u123">(value: "u123") => R.Result<"u123", never> (+1 overload)succeed('u123'),
  import RR.const andThen: <R.Result<"u123", never>, R.Failure<Error> | R.Success<string>>(fn: (a: "u123") => R.Failure<Error> | R.Success<string>) => (result: R.Result<"u123", never>) => R.Result<string, Error> (+1 overload)andThen(const validateUser: (id: string) => R.Failure<Error> | R.Success<string>validateUser),
  import RR.const map: <R.Result<string, Error>, {
    readonly id: string;
    readonly name: "John Doe";
}>(fn: (a: string) => {
    readonly id: string;
    readonly name: "John Doe";
}) => (result: R.Result<string, Error>) => R.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error> (+1 overload)
map(id: stringid => ({ id: stringid, name: "John Doe"name: 'John Doe' }))
);

if (import RR.const isSuccess: <{
    readonly id: string;
    readonly name: "John Doe";
}>(result: R.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, unknown>) => result is R.Success<{
    readonly id: string;
    readonly name: "John Doe";
}>
Type guard to check if a
Result
is a
Success
.
@function@typeParamT  - The type of the success value.@paramresult  - The Result to check.@returnstrue if the result is a Success, otherwise false.@exampleimport { Result } from '@praha/byethrow';

const result: Result.Result<number, string> = { type: 'Success', value: 10 };
if (Result.isSuccess(result)) {
  console.log(result.value); // Safe access to value
}
@categoryType  GuardsisSuccess(const result: R.Result<{
    readonly id: string;
    readonly name: "John Doe";
}, Error>
result)) {
  var console: ConsoleThe console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:

A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.

Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr

Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@seesourceconsole.Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout

See util.format() for more information.
@sincev0 .1.100log(const result: R.Success<{
    readonly id: string;
    readonly name: "John Doe";
}>
result.value: {
    readonly id: string;
    readonly name: "John Doe";
}
value);
}

Tree-Shaking Support

@praha/byethrow achieves complete tree-shaking support:

// Example: Usage in a small application
import { import RR } from '@praha/byethrow';

// Only these features are actually used
const const parseNumber: (input: string) => R.Result<number, Error>parseNumber = import RR.try<(input: string) => number, Error>(options: {
    try: (input: string) => number;
    catch: (error: unknown) => Error;
}): (input: string) => R.Result<number, Error> (+7 overloads)
export try
Wraps a function execution (sync or async) or a Promise in a
Result
or
ResultAsync
type,
capturing errors and returning them in a structured way.
You can use either a custom catch handler or rely on the safe: true option
to assume the function cannot throw.
@function@typeParamT  - The function type to execute (sync or async) or a Promise type.@typeParamE  - The error type to return if catch is used.@exampleSync  try-catch
import { Result } from '@praha/byethrow';

const fn = Result.try({
try: (x: number) => {
if (x < 0) throw new Error('Negative!');
return x * 2;
},
catch: (error) => new Error('Oops!', { cause: error }),
});

const result = fn(5); // Result.Result<number, Error>
@exampleSync  try-catch with immediate execution
import { Result } from '@praha/byethrow';

const result = Result.try({
immediate: true,
try: () => {
const x = Math.random() * 10 - 5;
if (x < 0) throw new Error('Negative!');
return x * 2;
},
catch: (error) => new Error('Oops!', { cause: error }),
});

// result is Result<number, Error>
@exampleSync  safe
import { Result } from '@praha/byethrow';

const fn = Result.try({
safe: true,
try: (x: number) => x + 1,
});

const result = fn(1); // Result.Result<number, never>
@exampleSync  safe with immediate execution
import { Result } from '@praha/byethrow';

const result = Result.try({
safe: true,
immediate: true,
try: () => Math.random() + 1,
});

// result is Result<number, never>
@exampleAsync  try-catch
import { Result } from '@praha/byethrow';

const fn = Result.try({
try: async (id: string) => await fetch(`/api/data/${id}`),
catch: (error) => new Error('Oops!', { cause: error }),
});

const result = await fn('abc'); // Result.ResultAsync<Response, Error>
@exampleAsync  try-catch with immediate execution
import { Result } from '@praha/byethrow';

const result = Result.try({
immediate: true,
try: () => fetch('/api/data'),
catch: (error) => new Error('Fetch failed', { cause: error }),
});

// result is ResultAsync<Response, Error>
@exampleAsync  safe
import { Result } from '@praha/byethrow';

const fn = Result.try({
safe: true,
try: async () => await Promise.resolve('ok'),
});

const result = await fn(); // Result.ResultAsync<string, never>
@exampleAsync  safe with immediate execution
import { Result } from '@praha/byethrow';

const result = Result.try({
safe: true,
immediate: true,
try: () => Promise.resolve('ok'),
});

// result is ResultAsync<string, never>
@categoryCreatorstry({
  try: (input: string) => numbertry: (input: stringinput: string) => function parseInt(string: string, radix?: number): numberConverts a string to an integer.
@paramstring  A string to convert into a number.@paramradix  A value between 2 and 36 that specifies the base of the number in string.
If this argument is not supplied, strings with a prefix of '0x' are considered hexadecimal.
All other strings are considered decimal.parseInt(input: stringinput, 10),
  catch: (error: unknown) => Errorcatch: () => new var Error: ErrorConstructor
new (message?: string, options?: ErrorOptions) => Error (+1 overload)
Error('Invalid number')
});

// In this case, only the minimal code required for parseNumber
// is included in the bundle, while other features (combine, pipe, etc.) are excluded

Best Practices

Choosing Between Import Methods

Use Result if you prefer explicit and descriptive naming that clearly indicates the purpose of each operation
Use R if you prefer fewer keystrokes and more concise code for faster development

Important: Avoid Mixing Import Methods

We strongly recommend against mixing Result and R within the same codebase. Choose one approach and stick with it consistently throughout your project to maintain code readability and consistency.

// @filename: mixed-imports.ts
// ❌ Don't mix approaches - this creates inconsistent code
import { import ResultResult, import RR } from '@praha/byethrow';

const const validateId: (id: string) => Result.Result<string, never>validateId = (id: stringid: string) => {
  return import ResultResult.const succeed: <string>(value: string) => Result.Result<string, never> (+1 overload)succeed(id: stringid); // Using Result
};

const const processData: Result.Result<string, never>processData = import RR.const pipe: <Result.Result<"data", never>, Result.Result<string, never>>(a: Result.Result<"data", never>, ab: (a: Result.Result<"data", never>) => Result.Result<string, never>) => Result.Result<string, never> (+25 overloads)pipe(  // Using R
  import RR.const succeed: <"data">(value: "data") => Result.Result<"data", never> (+1 overload)succeed('data'),
  import RR.const andThen: <Result.Result<"data", never>, Result.Result<string, never>>(fn: (a: "data") => Result.Result<string, never>) => (result: Result.Result<"data", never>) => Result.Result<string, never> (+1 overload)andThen(const validateId: (id: string) => Result.Result<string, never>validateId)
);

// @filename: consistent-imports.ts
// ✅ Choose one approach and use it consistently
import { import ResultResult } from '@praha/byethrow';

const const validateId: (id: string) => Result.Result<string, never>validateId = (id: stringid: string) => {
  return import ResultResult.const succeed: <string>(value: string) => Result.Result<string, never> (+1 overload)succeed(id: stringid);
};

const const processData: Result.Result<string, never>processData = import ResultResult.const pipe: <Result.Result<"data", never>, Result.Result<string, never>>(a: Result.Result<"data", never>, ab: (a: Result.Result<"data", never>) => Result.Result<string, never>) => Result.Result<string, never> (+25 overloads)pipe(
  import ResultResult.const succeed: <"data">(value: "data") => Result.Result<"data", never> (+1 overload)succeed('data'),
  import ResultResult.const andThen: <Result.Result<"data", never>, Result.Result<string, never>>(fn: (a: "data") => Result.Result<string, never>) => (result: Result.Result<"data", never>) => Result.Result<string, never> (+1 overload)andThen(const validateId: (id: string) => Result.Result<string, never>validateId)
);

Regardless of which method you choose, bundlers will automatically optimize your code, ensuring only the necessary features are included in your final bundle.

#Importing Result

#Two Import Methods

#Explicit Namespace Approach (Result)

#Shorthand Alias (R)

#Tree-Shaking Support

#Best Practices

#Choosing Between Import Methods

#Important: Avoid Mixing Import Methods

#Importing Result

#Two Import Methods

#Explicit Namespace Approach (Result)

#Shorthand Alias (R)

#Tree-Shaking Support

#Best Practices

#Choosing Between Import Methods

#Important: Avoid Mixing Import Methods

Importing Result

Two Import Methods

Explicit Namespace Approach (`Result`)

Shorthand Alias (`R`)

Tree-Shaking Support

Best Practices

Choosing Between Import Methods

Important: Avoid Mixing Import Methods

Importing Result

Two Import Methods

Explicit Namespace Approach (`Result`)

Shorthand Alias (`R`)

Tree-Shaking Support

Best Practices

Choosing Between Import Methods

Important: Avoid Mixing Import Methods