IO methods as valid Task monads perfect to write great point-free software in JavaScript that is compatible with most modern browsers and Deno.

• Buffer
• Directory
• File
• File System Collection
• Request
• Resource
• Response
• URL
• Browser safe
• File System
• Utilities
• TypeScript

Usage

This example uses the Ramda library - for simplification - but you should be able to use any library that implements the Fantasy-land specifications.

import { __, ap, chain, compose, lift, map, match, path, prop, useWith } from "https://deno.land/x/ramda@v0.27.2/mod.ts";
import Task from "https://deno.land/x/functional@v1.3.3/library/Task.js";
import { safeExtract } from "https://deno.land/x/functional@v1.3.3/library/utilities.js";
import Request from "https://deno.land/x/functional_io@v1.1.0/library/Request.js";
import { factorizeFile } from "https://deno.land/x/functional_io@v1.1.0/library/File.js";
import { fetch } from "https://deno.land/x/functional_io@v1.1.0/library/browser_safe.js";
import { writeFile } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const fetchBacon = compose(
  chain(writeFile({})),
  ap(
    useWith(
      lift(factorizeFile(__, __, 0)),
      [
        compose(
          Task.of,
          name => `${Deno.cwd()}/${name}.html`,
          prop(1),
          match(/\?type=([A-Za-z\-]+)/),
          path([ "headers", "url" ])
        ),
        map(prop("raw"))
      ]
    ),
    fetch
  )
);

const container = fetchBacon(
  Request.get("https://baconipsum.com/api/?type=all-meat&paras=3&start-with-lorem=1&format=html")
);

// Calling `fetchBacon` results in an instance of `Task` keeping the function pure.
assert(Task.is(container));

const file = safeExtract("Failed to write file.", await container.run());

assert(File.is(file));

Using the bundle

As a convenience, when using Functional IO in the browser, you can use the unminified bundled copy (18KB gzipped).

import { Task, safeExtract } from "https://deno.land/x/functional@v1.3.3/functional.js";
import { Request, Response, fetch } from "https://deno.land/x/functional_io@v1.1.0/functional-io.js";

const container = fetch(
  Request.get("https://baconipsum.com/api/?type=all-meat&paras=3&start-with-lorem=1&format=html")
);

assert(Task.is(container));

const response = safeExtract("Failed to fetch resource.", await container.run());

assert(Response.is(response));

---

Buffer

The Buffer is the most basic type; it only has one attribute which is a typed array named "raw". Any type that share the raw attribute is composable with Buffer (and each other) and interoperable.

The Buffer type implements the following algebras:

• Group
• Comonad
• Monad

Example

import Buffer from "https://deno.land/x/functional_io@v1.1.0/library/Buffer.js";

const buffer = Buffer.fromString("hoge").concat(Buffer.fromString("fuga"));

assert(Buffer.is(buffer));

---

Directory

The Directory type represents a directory on the file system. It is the only type with the same shape as URL. It has only one attributes: the path of the directory. A Directory is interoperable with a URL or a File. It also has interoperability with a File through the FileSystemCollection type.

The Directory type implements the following algebras:

• Ord
• Comonad
• Monad

Example

assert(Directory(`${Deno.cwd()}/hoge`).lte(Directory(`${Deno.cwd()}/piyo`)));

---

File

The File type extends the Resource type. It represents a file with a path. It has three attributes: the first is the path of the file, the second is a typed array named "raw" and the last is the Resource ID (rid). A File is composable and interoperable with a Resource or a Buffer -- It also has some interoperability with a Location through the FileSystemCollection.

The File type implements the following algebras:

• Group
• Bifunctor
• Comonad
• Monad

Example

const file = File(`${Deno.cwd()}/hoge`, new Uint8Array([ 65, 66, 67, 68, 69 ]), 3)
  .concat(File(`${Deno.cwd()}/piyo`, new Uint8Array([ 70, 71, 72, 73, 74 ]), 3));

assert(File.is(file));

---

File System Collection

The FileSystemCollection is represents a collection of Location, namely of Directory and File. This of it as an Array for those types.

The FileSystemCollection type implements the following algebras:

• Group
• Comonad
• Monad
• Traversable

Example

const containerA = Maybe.Just(42).map(x => x + 2);
const containerB = Maybe.Nothing.map(x => x + 2);

assert(Maybe.Just.is(containerA));
assert(containerA.extract() === 44);
assert(Maybe.Nothing.is(containerB));

---

File Group algebra law "Left identity" and "Right identity" is not respected because the rid can't be modified without using bimap.

---

Request

The Request represent a HTTP request. It has two attributes: the first is an object for the response "header" and the second is a typed array named "raw". The Request type is mostly interoperable with Resource, File and Response.

The Resource type implements the following algebras:

• Group
• Bifunctor
• Monad

Example

const request = Request({}, new Uint8Array([ 65, 66, 67, 68, 69 ]))
  .concat(Resource(new Uint8Array([ 70, 71, 72, 73, 74 ]), 3));

assert(Request.is(request));

Utilities

The Request namespace comes with 4 methods for convenience to create an instance of Request with a common verb. The methods are curried when necessary. Object → Unint8Array → Response

const container = compose(
  lift(Request.post({ ["Content-Type"]: "application/json" })),
  readFile
)(File.fromPath(`${Deno.cwd()}/hoge`));

assert((await container.run()).extract().headers.method === "POST");

Method name	Has 2 arguments
delete	DELETE
get	GET
post	POST
put	PUT

✢ The capitalized version of the methods were added because delete is a TypeScript reserved word.

---

Request Semigroup algebra law "Left identity" is not respected because the headers can't be modified without using bimap.

Request Monoid algebra law "Left identity" is not respected because the headers can't be modified without using bimap.

Request Group algebra law "Left identity" and "Right identity" is not respected because the headers can't be modified without using bimap.

Request Modnad algebra law "Right identity" is not respected because the headers can't be modified without using bimap.

Request Applicative algebra law "Interchange" is not respected because the headers can't be modified without using bimap.

---

Resource

The Resource type extends the Buffer type. It represents a system resource with a handle, eg: STDOUT, STDIN or a file. It has two attributes: the first is a typed array named "raw" and the second is the Resource ID (rid). Any type that share the Resource attributes is composable and interoperable.

The Resource type implements the following algebras:

• Group
• Bifunctor
• Comonad
• Monad

Example

const resource = Resource(new Uint8Array([ 65, 66, 67, 68, 69 ]), 3)
  .concat(Resource(new Uint8Array([ 70, 71, 72, 73, 74 ]), 3));

assert(Resource.is(resource));

---

Resource Monoid algebra law "Left identity" is not respected because the rid can't be modified without using bimap.

Resource Group algebra law "Left identity" and "Right identity" is not respected because the rid can't be modified without using bimap.

Resource Modnad algebra law "Right identity" is not respected because the rid can't be modified without using bimap.

Resource Applicative algebra law "Interchange" is not respected because the rid can't be modified without using bimap.

---

Response

The Response represent a HTTP response. It has two attributes: the first is an object for the response "header" and the second is a typed array named "raw". The Response type is mostly interoperable with Resource, File and Request.

The Resource type implements the following algebras:

• Alternative
• Group
• Bifunctor
• Monad

Example

const response = Response.Success({}, new Uint8Array([ 65, 66, 67, 68, 69 ]))
  .concat(Resource(new Uint8Array([ 70, 71, 72, 73, 74 ]), 3));

assert(Response.is(response));

Utilities

The Response namespace comes with 38 methods for convenience to create an instance of Response with a common status. The methods are curried: Object → Uint8Array → Response

const container = compose(
  lift(Response.OK({ ["Content-Type"]: "application/json" })),
  readFile
)(File.fromPath(`${Deno.cwd()}/hoge`));

assert((await container.run()).extract().headers.status === 200);

Method name	Status
OK	200
Created	201
Accepted	202
NoContent	204
MultipleChoice	300
MovePermanently	301
Found	302
NotModified	304
TemporaryRedirect	307
PermanentRedirect	308
BadRequest	400
Unauthorized	401
Forbidden	403
NotFound	404
MethodNotAllowed	405
NotAcceptable	406
RequestTimeout	408
Conflict	409
Gone	410
ImATeapot	418
InternalServerError	500
NotImplemented	501
BadGateway	502
ServiceUnavailable	503
GatewayTimeout	504
PermissionDenied	550

---

Response Semigroup algebra law "Left identity" is not respected because the headers can't be modified without using bimap.

Response Monoid algebra law "Left identity" is not respected because the headers can't be modified without using bimap.

Response Group algebra law "Left identity" and "Right identity" is not respected because the headers can't be modified without using bimap.

Response Modnad algebra law "Right identity" is not respected because the headers can't be modified without using bimap.

Response Applicative algebra law "Interchange" is not respected because the headers can't be modified without using bimap.

---

URL

The URL type represents an URL; either of a location on the file system or on a remote server. It has only one attributes: the path of the URL. A URL is interoperable with a File or a Directory. It also has interoperability with a File or a Directory through the FileSystemCollection type.

The URL type implements the following algebras:

• Ord
• Comonad
• Monad

Example

assert(URL(`${Deno.cwd()}/hoge`).lte(URL(`${Deno.cwd()}/piyo`)));

---

Browser safe

pureFetch

Request → Task e Response

Fetches a resource on a local/remote server.

import { fetch } from "https://deno.land/x/functional_io@v1.1.0/library/browser-safe.js";

const containerA = fetch(Request.GET("http://localhost:8000"));

assert(Task.is(containerA));

const containerB = await container.run().extract();

assert(Response.Success.is(containerB));

---

File System

⚠️ Note Deno.cwd is used in the following example; if you use Deno.cwd to compose your paths, your functions are no longer pure.

chdir 📕

Directory → Task e Directory

Change the current working directory to the specified path.

import { chdir } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = chdir(Directory(".."));

assert(Task.is(container));

chmod 📕

Number → File → Task e File

Changes the permission of a specific file/directory of specified path. Ignores the process's umask.

import { chmod } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = chmod(0o000, File.fromPath(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

chown 📕

Number → Number → File → Task e File

Change owner of a regular file or directory. This functionality is not available on Windows.

import { chown } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = chown(null, null, File.fromPath(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

close 📕

Resource → Task e Resource

Close the given resource which has been previously opened, such as via opening or creating a file. Closing a file when you are finished with it is important to avoid leaking resources.

import { close } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = close(File(`${Deno.cwd()}/hoge`, new Uint8Array([]), 3));

assert(Task.is(container));

copy 📕

Object → Buffer a → Buffer b → Task e Buffer b

Copies from a source to a destination until either EOF (null) is read from the source, or an error occurs.

import { copy } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = copy({}, Buffer(new Uint8Array([ 65, 66, 67, 68, 69 ])), Buffer(new Uint8Array([])));

assert(Task.is(container));

copyFile 📕

File a → File b → Task e File b

Copies the contents and permissions of one file to another specified file, by default creating a new file if needed, else overwriting. Fails if target path is a directory or is unwritable.

import { copyFile } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = copyFile(File.fromPath(`${Deno.cwd()}/hoge`), File.fromPath(`${Deno.cwd()}/piyo`));

assert(Task.is(container));

create 📕

File → Task e File

Creates a file if none exists or truncates an existing file.

import { create } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = create(File.fromPath(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

cwd 📕

Return a Directory representation of the current working directory. () → Task e Directory

import { cwd } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = cwd();

assert(Task.is(container));

ensureDir 📕

Directory → Task e Directory

Ensures that the directory exists. If the directory structure does not exist, it is created. Like mkdir -p.

import { ensureDir } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = emptyDir(Directory(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

exists 📕

`URL → Task e|null URL

Test whether the given path exists by checking with the file system. If the file or directory doesn't exist, it will resolve to Either.Left(null).

import { exists } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = exists(Directory(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

mkdir 📕

Object → Directory → Task e Directory

Creates a new directory with the specified path.

import { mkdir } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = mkdir({}, Directory(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

move 📕

Object → String → URL → Task e URL

Moves a file or directory.

import { move } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = move({}, `${Deno.cwd()}/piyo`, Directory(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

open 📕

Object → File → Task e File

Open a file and resolve to an instance of File. The file does not need to previously exist if using the create or createNew open options. It is the callers responsibility to close the file when finished with it.

import { open } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = open({ read: true, write: true }, File.fromPath(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

read 📕

Resource Task e Resource

Read from a Resource given it has a non-zero raw buffer.

import { read } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = read(File(`${Deno.cwd()}/hoge`, new Uint8Array(5), 3));

assert(Task.is(container));

readLine

Resource → Task e Resource

Read from a Resource to the CLRF.

import { readLine } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = readLine(File(`${Deno.cwd()}/hoge`, new Uint8Array([]), 3));

assert(Task.is(container));

readNBytes

Number → Resource → Task e Resource

Read N bytes from a Resource.

import { readNBytes } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = readNBytes(5, File(`${Deno.cwd()}/hoge`, new Uint8Array([]), 3));

assert(Task.is(container));

readOneByte

Resource → Task e Resource

Read 1 byte from a Resource.

import { readOneByte } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = readOneByte(File(`${Deno.cwd()}/hoge`, new Uint8Array([]), 3));

assert(Task.is(container));

readAll 📕

Resource → Task e Resource

Read from a Resource.

import { readAll } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = readAll(File(`${Deno.cwd()}/hoge`, new Uint8Array([]), 3));

assert(Task.is(container));

readFile 📕

File → Task e File

Read from a File.

import { readFile } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = readFile(File(`${Deno.cwd()}/hoge`, new Uint8Array([]), 3));

assert(Task.is(container));

remove 📕

Object → URL → Task e URL

Removes the named file or directory.

import { remove } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = remove({ recursive: true }, Directory.fromPath(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

rename 📕

String → URL → Task e URL

Renames a file or directory.

import { rename } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = rename(`${Deno.cwd()}/piyo`, Directory(`${Deno.cwd()}/hoge`));

assert(Task.is(container));

write 📕

Resource → Task e Resource

Write to a Resource given it has a non-zero raw buffer.

import { write } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = write(File(`${Deno.cwd()}/hoge`, new Uint8Array([ 65, 66, 67, 68, 69 ]), 3));

assert(Task.is(container));

writeAll 📕

Buffer → Task e Resource

Write all to a Resource from a Buffer.

import { writeAll } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = writeAll(
  Buffer(new Uint8Array([ 65, 66, 67, 68, 69 ])),
  File(`${Deno.cwd()}/hoge`, new Uint8Array([]), 3)
);

assert(Task.is(container));

writeFile 📕

Object → File → Task e File

Write a File to the file system.

import { writeFile } from "https://deno.land/x/functional_io@v1.1.0/library/fs.js";

const container = writeFile({}, File(`${Deno.cwd()}/hoge`, new Uint8Array([]), 3));

assert(Task.is(container));

---

Utilities

findCLRFIndex

Uint8Array → Number

This function takes a Uint8Array and, returns the index of the last character of the first CLRF sequence encountered.

import { findCLRFIndex } from "https://deno.land/x/functional_io@v1.1.0/library/utilities.js";

assertEquals(findCLRFIndex(new Uint8Array([ 104, 111, 103, 101, 13, 10 ])), 6);

discardFirstLine

Uint8Array → Uint8Array

This function takes a Uint8Array and, returns the typed array minus the first line separated by CLRF.

import { discardFirstLine } from "https://deno.land/x/functional_io@v1.1.0/library/utilities.js";

assertEquals(
  discardFirstLine(new Uint8Array([ 104, 111, 103, 101, 13, 10, 104, 111, 103, 101, 13, 10 ])),
  new Uint8Array([ 104, 111, 103, 101, 13, 10 ])
);

discardNCharacter

Number → Uint8Array → Uint8Array

This function takes a Number, a Uint8Array and, returns the typed array minus the specified amount of character starting from the left side.

import { discardNCharacter } from "https://deno.land/x/functional_io@v1.1.0/library/utilities.js";

assertEquals(
  discardNCharacter(1, new Uint8Array([ 104, 111, 103, 101, 13, 10 ])),
  new Uint8Array([ 111, 103, 101, 13, 10 ])
);

getFirstLine

Uint8Array → Uint8Array

This function takes a Uint8Array and, returns the first line separated by a CLRF inclusively.

import { getFirstLine } from "https://deno.land/x/functional_io@v1.1.0/library/utilities.js";

assertEquals(
  getFirstLine(new Uint8Array([ 104, 111, 103, 101, 13, 10, 104, 111, 103, 101, 13, 10 ])),
  new Uint8Array([ 104, 111, 103, 101, 13, 10 ])
);

joinCLRF

Uint8Array[] → Uint8Array

This function takes a list of Uint8Array and, returns a Uint8Array of the list joined with CLRF sequence; the function is analogous to Array#join.

import { joinCLRF } from "https://deno.land/x/functional_io@v1.1.0/library/utilities.js";

assertEquals(
  joinCLRF(
    [
      new Uint8Array([ 104, 111, 103, 101 ]),
      new Uint8Array([ 104, 111, 103, 101 ])
    ]
  ),
  new Uint8Array([ 104, 111, 103, 101, 13, 10, 104, 111, 103, 101, 13, 10 ])
);

splitCLRF

Uint8Array → Uint8Array[]

This function takes a Uint8Array and, returns a list of Uint8Array of subarray split at the CLRF sequence; the function is analogous to String#split.

import { splitCLRF } from "https://deno.land/x/functional_io@v1.1.0/library/utilities.js";

assertEquals(
  splitCLRF(new Uint8Array([ 104, 111, 103, 101, 13, 10, 104, 111, 103, 101, 13, 10 ])),
  [
    new Uint8Array([ 104, 111, 103, 101, 13, 10 ]),
    new Uint8Array([ 104, 111, 103, 101, 13, 10 ])
  ]
);

trimCRLF

Uint8Array → Uint8Array

This function takes a Uint8Array and, returns a typed array minus CRLF at the beginning and at the end; the function is analogous to String#trim.

import { trimCRLF } from "https://deno.land/x/functional_io@v1.1.0/library/utilities.js";

assertEquals(
  trimCRLF(new Uint8Array([ 104, 111, 103, 101, 13, 10 ])),
  new Uint8Array([ 104, 111, 103, 101 ])
);

factorizeUint8Array

`Number|Array|Uint8Array → Uint8Array

This function factorize a Uint8Array given an argument.

---

TypeScript

You can import any types.

import {
  Buffer,
  Directory,
  File,
  Request,
  Resource,
  Response,
  URL
} from "https://deno.land/x/functional_io@v1.1.0/mod.ts";

Or, you can import individual sub-module with the appropriate TypeScript hint in Deno.

// @deno-types="https://deno.land/x/functional_io@v1.1.0/library/Request.d.ts"
import Request from "https://deno.land/x/functional_io@v1.1.0/library/Request.js";

---

Contributing

We appreciate your help! Please, read the guidelines.

License

Copyright © 2020 - Sebastien Filion

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.