One important feature of an Effect application is that layers are shared by default. This means that if the same layer is used twice, and if we provide the layer globally, the layer will only be allocated a single time. For every layer in our dependency graph, there is only one instance of it that is shared between all the layers that depend on it.
Example
For example, assume we have the three services A, B, and C. The implementation of both B and C is dependent on the A service:
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Feeds the output services of this builder into the input of the specified
builder, resulting in a new builder with the inputs of this builder as
well as any leftover inputs, and the outputs of the specified builder.
Feeds the output services of this builder into the input of the specified
builder, resulting in a new builder with the inputs of this builder as
well as any leftover inputs, and the outputs of the specified builder.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Feeds the output services of this builder into the input of the specified
builder, resulting in a new builder with the inputs of this builder as
well as any leftover inputs, and the outputs of the specified builder.
Feeds the output services of this builder into the input of the specified
builder, resulting in a new builder with the inputs of this builder as
well as any leftover inputs, and the outputs of the specified builder.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
If we don’t provide a layer globally but instead provide them locally, that layer doesn’t support memoization by default.
Example
In the following example, we provided the ALive layer two times locally, and Effect doesn’t memoize the construction of the ALive layer.
So, it will be initialized two times:
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
We can memoize a layer manually using the Layer.memoize function.
It will return a scoped effect that, if evaluated, will return the lazily computed result of this layer.
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Scopes all resources used in this workflow to the lifetime of the workflow,
ensuring that their finalizers are run as soon as this workflow completes
execution, whether by success, failure, or interruption.
Use andThen when you need to run multiple actions in sequence, with the
second action depending on the result of the first. This is useful for
combining effects or handling computations that must happen in order.
Details
The second action can be:
A constant value (similar to
as
)
A function returning a value (similar to
map
)
A Promise
A function returning a Promise
An Effect
A function returning an Effect (similar to
flatMap
)
Note:andThen works well with both Option and Either types,
treating them as effects.
@example
// Title: Applying a Discount Based on Fetched Amount
import { pipe, Effect } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
