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Effect Documentation

Effect 3.18 (Release)

Tim Smart
Tim Smart
Founding Engineer

Effect 3.18 has been released! This release includes a number of new features and improvements. Here’s a summary of what’s new:

Graph module

An experimental Graph module has been added, with comprehensive graph data structure support.

The Graph module provides:

  • Directed and undirected graph support
  • Immutable and mutable graph variants
  • Type-safe node and edge operations
  • Graph algorithms: DFS, BFS, shortest paths, cycle detection, etc.
import { Graph } from "effect"


// Create a graph with mutations
const graph = Graph.directed<string, number>((mutable) => {
  const nodeA = Graph.addNode(mutable, "Node A")
  const nodeB = Graph.addNode(mutable, "Node B")
  Graph.addEdge(mutable, nodeA, nodeB, 5)
})


console.log(`Nodes: ${Graph.nodeCount(graph)}, Edges: ${Graph.edgeCount(graph)}`)

Context.ReadonlyTag

The ReadonlyTag type is the covariant side of a Context.Tag, that can be used to constrain tags that match a certain service shape.

import type { Context } from "effect"
import { Effect } from "effect"


export class MyRequirement extends Effect.Service<MyRequirement>()(
  "MyRequirement",
  { succeed: () => 42 }
) {}


export class MyUseCase extends Effect.Service<MyUseCase>()("MyUseCase", {
  dependencies: [MyRequirement.Default],
  effect: Effect.gen(function* () {
    const requirement = yield* MyRequirement
    return Effect.fn("MyUseCase.execute")(function* () {
      return requirement()
    })
  })
}) {}


export function effectHandler<I, Args extends Array<any>, A, E, R>(
  service: Context.ReadonlyTag<I, (...args: Args) => Effect.Effect<A, E, R>>
) {
  return Effect.fn("effectHandler")(function* (...args: Args) {
    const execute = yield* service
    yield* execute(...args)
  })
}


export const program = effectHandler(MyUseCase)

Other changes

  • resize method has been added to Effect.Semaphore, allowing dynamic adjustment of a semaphore’s permits.

There were several other smaller changes made. Take a look through the CHANGELOG to see them all: CHANGELOG.

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