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https://github.com/zio/zio-direct
Direct-Style Programming for ZIO
https://github.com/zio/zio-direct
async-await effect-system functional-programming meta-programming scala
Last synced: about 1 month ago
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Direct-Style Programming for ZIO
- Host: GitHub
- URL: https://github.com/zio/zio-direct
- Owner: zio
- Created: 2022-10-24T14:27:00.000Z (about 2 years ago)
- Default Branch: main
- Last Pushed: 2023-06-02T07:44:28.000Z (over 1 year ago)
- Last Synced: 2024-04-23T05:29:28.352Z (8 months ago)
- Topics: async-await, effect-system, functional-programming, meta-programming, scala
- Language: Scala
- Homepage: https://zio.dev/zio-direct
- Size: 6.13 MB
- Stars: 149
- Watchers: 11
- Forks: 13
- Open Issues: 13
-
Metadata Files:
- Readme: README.md
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README
[//]: # (This file was autogenerated using `zio-sbt-website` plugin via `sbt generateReadme` command.)
[//]: # (So please do not edit it manually. Instead, change "docs/index.md" file or sbt setting keys)
[//]: # (e.g. "readmeDocumentation" and "readmeSupport".)
# ZIO Direct Style
ZIO Direct Style is a library that allows using directly-style i.e. imperative programming with ZIO effects which is based on the Monadless paradigm.
[](https://github.com/zio/zio/wiki/Project-Stages)  [](https://oss.sonatype.org/content/repositories/releases/dev/zio/zio-direct_3/) [](https://oss.sonatype.org/content/repositories/snapshots/dev/zio/zio-direct_3/) [](https://javadoc.io/doc/dev.zio/zio-direct-docs_3) [](https://github.com/zio/zio-direct)
## Installation
To use zio-direct, add the following to your `build.sbt` file.
```scala
libraryDependencies += "dev.zio" %% "zio-direct" % "1.0.0-RC7"
```
You can also use zio-direct with ZStream and ZPure by importing the following modules.
> Currently this is only supported in Scala 3.
```scala
// ZStream
libraryDependencies += "dev.zio" %% "zio-direct-streams" % "1.0.0-RC7"
// ZPure
libraryDependencies += "dev.zio" %% "zio-direct-pure" % "1.0.0-RC7"
```
See the [Other Supported Monads](docs/other-supported-monads.md) section for more details.
## IDE Support
The preferred IDE to use with ZIO-Direct is Visual Studio Code + Metals. This is because Metals correctly reads the returns from `defer` calls directly from the Scala compiler which is not the case of IntelliJ. To remedy this issue, a Library Extension is provided for ZIO-Direct. See the [IntelliJ Support](docs/intellij-support.md) section for more details.
## Introduction
Talk at Functional Scala 2022:
* Video - https://www.youtube.com/watch?v=DgqfLfzq5eo
* Slides - https://www.slideshare.net/deusaquilus/ziodirect-functional-scala-2022
ZIO-Direct allows direct style programming with ZIO. This library provides a *syntactic sugar* that is more powerful than for-comprehensions as well as more natural to use. Simply add the `.run` suffix to any ZIO effect in order to retrieve its value.
ZIO-Direct works by using macros to rewrite sequential code into flatMap-chains based on the [Monadless](https://github.com/monadless/monadless) paradigm. The values resulting in `.run` calls from the ZIO effects are not actually awaited. Instead, they are rolled-up into a chain of flatMaps.
For example, in imperative programming operations typically are done in a simple set of steps.
```scala
object FileOps:
def read(file: File): String
def write(file: File, content: String): Unit
val textA = read(fileA)
val textB = read(fileB)
write(fileC, textA + textB)
```
Using functional programming, the equivalent of this functionality is a set of nested flatMap-chains.
```scala
object FileOps
def read(file: File): ZIO[Any, Throwable, String]
def write(file: File, content: String): ZIO[Any, Throwable, Unit]
read(fileA).flatMap { textA =>
read(fileB).flatMap { textB =>
write(fileC, textA + textB)
}
}
```
In order to avoid this complexity scala provides a for-comprehension syntactic sugar.
```scala
for {
textA <- read(fileA)
textB <- read(fileB)
_ <- write(fileC, textA + textB)
} yield ()
```
Unfortunately this syntactic sugar is limited in many cases, for example, inserting a conditional value inside is impossible.
```scala
for {
textA <- read(fileA)
// Not a possible syntax
if (fileA.contains("some string")) {
textB <- read(fileB)
_ <- write(fileC, textA + textB)
}
} yield ()
```
ZIO-Direct offers an equivalent syntactic sugar that is more ergonomic and allows many constructs that for-comprehensions do not.
```scala
defer {
val textA = read(fileA).run
if (fileA.contains("some string")) {
val textB = read(fileB).run
write(fileC, textA + textB).run
}
}
```
# ZIO-Tailored
ZIO-Direct is specifically tailored to ZIO capabilities as it supports Environment and Error composition in ZIO effects similar to the for-comprehension.
```scala
val out: ZIO[CustomerConfig & DistributorConfig, CustomerGetException | DistrubutorGetException, (Customer, Distributor)] =
defer {
// Get a customer-configuration object from the environment and extract its .url field
val custUrl: String = ZIO.service[CustomerConfig].run.url
// Get a distributor-configuration from the environment and extract its .url field
val distUrl: String = ZIO.service[DistributorConfig].run.url
(
// Use the two configurations to make an HTTP-call
parseCustomer(httpGetCustomer(custUrl).run),
parseDistrubutor(httpGetDistributor(distUrl).run)
)
}
```
## Branching and Looping Support
Unlike the for-comprehension, ZIO-Direct supports branching and looping in the use of flatMaps composition.
Let's have a look at a another non-trivial example.
```scala
class Database:
def nextRow(): ZIO[Any, Throwable, Row]
def hasNextRow(): ZIO[Any, Throwable, Boolean]
def lockNextRow(): ZIO[Any, Throwable, Boolean]
object Database:
def open: ZIO[Any, Throwable, Database]
defer {
// Open a database connection
val db = Database.open().run
// See if there is is a next-row
while (db.hasNextRow().run) {
// try to lock, if aquired continue
if (db.lockNextRow().run)
val nextRow = db.nextRow().run
doSomethingWith(nextRow)
else
waitT()
}
}
```
> NOTE: The above database-api is imaginary.
The above code needs to be translated into something like this:
```scala
Database.open.flatMap { db =>
def whileFun(): ZIO[Any, Throwable, Unit] =
db.hasNextRow().flatMap { hasNextRow =>
if (hasNextRow)(
db.lockNextRow().flatMap { lockNextRow =>
if (!lockNextRow)
db.nextRow().map(nextRow => doSomethingWith(nextRow))
else
ZIO.succeed(waitT())
}
).flatMap(_ => whileFun())
else
ZIO.unit
}
whileFun()
}
```
Note that normally this is the exact code that would have to be written to capture such functionality For-comprehensions do not provide a way to do looping and branching so in such cases
a combination of flatMaps and recursion is necessary to avoid calling effects unnecessarily.
## Great for Refs and FiberRefs!
ZIO-direct makes it much easier to use ZIO mutable Ref and FiberRef variables. Since retrieveing and updating Ref and FiberRef variables requries a flatMap/for-comprehension call, it is typically very difficult to use them with branching/looping constructs. ZIO-direct makes these cases much easier.
```scala
class DatabaseApi {
val connRef = FiberRef.make[Option[Connection]](None)
def openConnection(): Connection = lowLevelDatabaseApi.openConnection()
def transaction(action: Action) =
defer {
val conn = connRef.get.run
if (conn == None) {
connRef.set(Some(openConnection())).run
}
val conn1 = connRef.get.run
conn.execute(action).run
}
}
```
Instead of having to write the following code:
```scala
class DatabaseApi {
val connRef = FiberRef.make[Option[Connection]](None)
def openConnection(): Connection = lowLevelDatabaseApi.openConnection()
def transaction(action: Action) =
connRef.get.flatMap { conn =>
(if (conn == None) {
connRef.set(Some(openConnection()))
} else {
ZIO.unit
}).flatMap(_ => connRef.get.flatMap { conn1 =>
conn1.execute(action)
})
}
// Note that for-comprehensions do not help very much in this use-case
def transaction0(action: Action) =
for {
conn <- connRef.get
_ <- if (conn == None) {
connRef.set(Some(openConnection()))
} else {
ZIO.unit
}
conn1 <- connRef.get
_ <- conn1.execute(action)
}
}
```
## Documentation
Learn more on the [ZIO Direct Style homepage](https://zio.dev/zio-direct)!
## Contributing
For the general guidelines, see ZIO [contributor's guide](https://zio.dev/about/contributing).
## Code of Conduct
See the [Code of Conduct](https://zio.dev/about/code-of-conduct)
## Support
Come chat with us on [![Badge-Discord]][Link-Discord].
[Badge-Discord]: https://img.shields.io/discord/629491597070827530?logo=discord "chat on discord"
[Link-Discord]: https://discord.gg/2ccFBr4 "Discord"
## License
[License](LICENSE)