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feat(tests): add type-tests and strict error handling examples
Addresses blocking review requirements: 1. Use Match.exhaustive instead of Match.orElse in examples - Forces handling ALL schema-defined HTTP error statuses - No escape hatch that could mask unhandled cases 2. Add type-tests proving literal union preservation - expectTypeOf tests verify status is literal (200, 404, 500) not number - Proves HttpError status is union from schema (404 | 500), not number 3. Add @ts-expect-error negative tests - Proves success status cannot be error status (e.g., 200 !== 404) - Proves error status cannot be success status 4. Add strict-error-handling.ts example with E=never - Demonstrates Effect<void, never, HttpClient> after catchTags - All _tag variants handled: HttpError, TransportError, UnexpectedStatus, UnexpectedContentType, ParseError, DecodeError - Match.exhaustive in all HttpError handlers This commit proves: - Type correlation (status -> body) is preserved - Literal union types don't degrade to 'number' - E=never is achievable with proper error handling Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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‎packages/app/examples/strict-error-handling.ts‎

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// CHANGE: Strict example demonstrating forced E=never error handling
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// WHY: Prove that after catchTags with Match.exhaustive, the error channel becomes 'never'
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// QUOTE(ТЗ): "Приёмка по смыслу: после catchTags(...) тип ошибки становится never"
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// REF: PR#3 blocking review from skulidropek
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// SOURCE: n/a
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// PURITY: SHELL
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// EFFECT: Effect<void, never, HttpClient> - all errors handled
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import * as FetchHttpClient from "@effect/platform/FetchHttpClient"
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import type * as HttpClient from "@effect/platform/HttpClient"
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import { Console, Effect, Exit, Match } from "effect"
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import { createClient, type ClientOptions } from "../src/shell/api-client/create-client.js"
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import { dispatchercreatePet, dispatchergetPet, dispatcherlistPets } from "../src/generated/dispatch.js"
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import type { Paths } from "../tests/fixtures/petstore.openapi.js"
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/**
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* Client configuration
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*/
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const clientOptions: ClientOptions = {
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baseUrl: "https://petstore.example.com",
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credentials: "include"
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}
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const apiClient = createClient<Paths>(clientOptions)
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// =============================================================================
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// STRICT EXAMPLE 1: getPet - handles 404, 500 + all boundary errors
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// =============================================================================
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/**
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* CRITICAL: This program has E=never - all errors are explicitly handled!
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*
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* The reviewer requires:
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* 1. Only Match.exhaustive (no Match.orElse)
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* 2. All _tag variants handled via catchTags
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* 3. After catchTags, type becomes Effect<void, never, HttpClient>
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*
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* Schema: getPet has responses 200 (success), 404 (error), 500 (error)
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* Error channel: HttpError<404 | 500> | BoundaryError
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*
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* @invariant After catchTags, E = never
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* @effect Effect<void, never, HttpClient>
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*/
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export const getPetStrictProgram: Effect.Effect<void, never, HttpClient.HttpClient> = Effect.gen(function*() {
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yield* Console.log("=== getPet: Strict Error Handling ===")
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// Execute request - yields only on 200
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const result = yield* apiClient.GET(
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"/pets/{petId}",
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dispatchergetPet,
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{ params: { petId: "123" } }
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)
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// Success! TypeScript knows status is 200
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yield* Console.log(`Got pet: ${result.body.name}`)
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}).pipe(
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// Handle HttpError with EXHAUSTIVE matching (no orElse!)
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Effect.catchTag("HttpError", (error) =>
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Match.value(error.status).pipe(
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Match.when(404, () => Console.log(`Not found: ${JSON.stringify(error.body)}`)),
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Match.when(500, () => Console.log(`Server error: ${JSON.stringify(error.body)}`)),
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// CRITICAL: Match.exhaustive - forces handling ALL schema statuses
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// If a new status (e.g., 401) is added to schema, this will fail typecheck
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Match.exhaustive
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)),
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// Handle ALL boundary errors
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Effect.catchTag("TransportError", (e) => Console.log(`Transport error: ${e.error.message}`)),
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Effect.catchTag("UnexpectedStatus", (e) => Console.log(`Unexpected status: ${e.status}`)),
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Effect.catchTag("UnexpectedContentType", (e) => Console.log(`Unexpected content-type: ${e.actual}`)),
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Effect.catchTag("ParseError", (e) => Console.log(`Parse error: ${e.error.message}`)),
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Effect.catchTag("DecodeError", (e) => Console.log(`Decode error: ${e.error.message}`))
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)
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// =============================================================================
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// STRICT EXAMPLE 2: createPet - handles 400, 500 + all boundary errors
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// =============================================================================
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/**
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* createPet strict handler
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*
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* Schema: createPet has responses 201 (success), 400 (error), 500 (error)
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* Error channel: HttpError<400 | 500> | BoundaryError
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*
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* @invariant After catchTags, E = never
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* @effect Effect<void, never, HttpClient>
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*/
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export const createPetStrictProgram: Effect.Effect<void, never, HttpClient.HttpClient> = Effect.gen(function*() {
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yield* Console.log("=== createPet: Strict Error Handling ===")
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const result = yield* apiClient.POST(
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"/pets",
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dispatchercreatePet,
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{
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body: JSON.stringify({ name: "Fluffy", tag: "cat" }),
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headers: { "Content-Type": "application/json" }
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}
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)
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// Success! TypeScript knows status is 201
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yield* Console.log(`Created pet: ${result.body.id}`)
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}).pipe(
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// Handle HttpError with EXHAUSTIVE matching
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Effect.catchTag("HttpError", (error) =>
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Match.value(error.status).pipe(
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Match.when(400, () => Console.log(`Validation error: ${JSON.stringify(error.body)}`)),
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Match.when(500, () => Console.log(`Server error: ${JSON.stringify(error.body)}`)),
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// Match.exhaustive forces handling 400 AND 500
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Match.exhaustive
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)),
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// Handle ALL boundary errors
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Effect.catchTag("TransportError", (e) => Console.log(`Transport error: ${e.error.message}`)),
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Effect.catchTag("UnexpectedStatus", (e) => Console.log(`Unexpected status: ${e.status}`)),
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Effect.catchTag("UnexpectedContentType", (e) => Console.log(`Unexpected content-type: ${e.actual}`)),
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Effect.catchTag("ParseError", (e) => Console.log(`Parse error: ${e.error.message}`)),
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Effect.catchTag("DecodeError", (e) => Console.log(`Decode error: ${e.error.message}`))
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)
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// =============================================================================
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// STRICT EXAMPLE 3: listPets - handles 500 + all boundary errors
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// =============================================================================
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/**
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* listPets strict handler
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*
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* Schema: listPets has responses 200 (success), 500 (error)
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* Error channel: HttpError<500> | BoundaryError
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*
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* @invariant After catchTags, E = never
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* @effect Effect<void, never, HttpClient>
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*/
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export const listPetsStrictProgram: Effect.Effect<void, never, HttpClient.HttpClient> = Effect.gen(function*() {
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yield* Console.log("=== listPets: Strict Error Handling ===")
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const result = yield* apiClient.GET(
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"/pets",
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dispatcherlistPets,
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{ query: { limit: 10 } }
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)
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// Success! TypeScript knows status is 200
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yield* Console.log(`Got ${result.body.length} pets`)
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}).pipe(
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// Handle HttpError with EXHAUSTIVE matching
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Effect.catchTag("HttpError", (error) =>
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Match.value(error.status).pipe(
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Match.when(500, () => Console.log(`Server error: ${JSON.stringify(error.body)}`)),
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// Match.exhaustive - only 500 needs handling for listPets
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Match.exhaustive
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)),
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// Handle ALL boundary errors
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Effect.catchTag("TransportError", (e) => Console.log(`Transport error: ${e.error.message}`)),
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Effect.catchTag("UnexpectedStatus", (e) => Console.log(`Unexpected status: ${e.status}`)),
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Effect.catchTag("UnexpectedContentType", (e) => Console.log(`Unexpected content-type: ${e.actual}`)),
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Effect.catchTag("ParseError", (e) => Console.log(`Parse error: ${e.error.message}`)),
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Effect.catchTag("DecodeError", (e) => Console.log(`Decode error: ${e.error.message}`))
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)
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// =============================================================================
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// MAIN: Run all strict programs
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// =============================================================================
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/**
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* Main program combines all strict examples
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* Type annotation proves E=never: Effect<void, never, HttpClient>
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*/
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const mainProgram: Effect.Effect<void, never, HttpClient.HttpClient> = Effect.gen(function*() {
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yield* Console.log("========================================")
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yield* Console.log(" Strict Error Handling Examples")
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yield* Console.log(" (All have E=never)")
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yield* Console.log("========================================\n")
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// All these programs have E=never - errors fully handled
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yield* getPetStrictProgram
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yield* Console.log("")
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yield* createPetStrictProgram
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yield* Console.log("")
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yield* listPetsStrictProgram
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yield* Console.log("\n========================================")
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yield* Console.log(" All errors handled - E=never verified!")
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yield* Console.log("========================================")
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})
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/**
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* Execute the program
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*
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* CRITICAL: Since mainProgram has E=never, Effect.runPromiseExit
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* will never fail with a typed error - only defects are possible.
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*/
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const program = mainProgram.pipe(
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Effect.provide(FetchHttpClient.layer)
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)
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const main = async () => {
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const exit = await Effect.runPromiseExit(program)
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if (Exit.isFailure(exit)) {
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// This can only be a defect (unexpected exception), not a typed error
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console.error("Unexpected defect:", exit.cause)
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}
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}
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main()

‎packages/app/examples/test-create-client.ts‎

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Original file line numberDiff line numberDiff line change
@@ -72,6 +72,7 @@ const listAllPetsExample = Effect.gen(function*() {
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* Example program: Get specific pet
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*
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* Demonstrates handling multiple HTTP error statuses (404, 500).
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* Uses Match.exhaustive to force handling ALL schema-defined statuses.
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*
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* @pure false - performs HTTP request
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*/
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yield* Console.log(`Success: Got pet "${result.body.name}"`)
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yield* Console.log(` Tag: ${result.body.tag ?? "none"}`)
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}).pipe(
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// Handle HTTP errors using Match for exhaustive pattern matching
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// Handle HTTP errors using Match.exhaustive - forces handling ALL schema statuses
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// CRITICAL: Match.exhaustive, not Match.orElse!
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Effect.catchTag("HttpError", (error) =>
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Match.value(error.status).pipe(
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Match.when(404, () => Console.log(`Not found: ${JSON.stringify(error.body)}`)),
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Match.when(500, () => Console.log(`Server error: ${JSON.stringify(error.body)}`)),
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Match.orElse(() => Console.log(`Unexpected HTTP error: ${error.status}`))
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Match.exhaustive // Forces handling all 404 | 500 - no escape hatch
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)),
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Effect.catchTag("TransportError", (error) =>
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Console.log(`Transport error: ${error.error.message}`))
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* Example program: Create new pet
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*
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* Demonstrates handling validation errors (400).
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* Uses Match.exhaustive to force handling ALL schema-defined statuses.
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*
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* @pure false - performs HTTP request
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*/
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yield* Console.log(` Name: ${result.body.name}`)
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}).pipe(
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// Handle HTTP errors - FORCED by TypeScript!
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// CRITICAL: Match.exhaustive, not Match.orElse!
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Effect.catchTag("HttpError", (error) =>
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Match.value(error.status).pipe(
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Match.when(400, () => Console.log(`Validation error: ${JSON.stringify(error.body)}`)),
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Match.when(500, () => Console.log(`Server error: ${JSON.stringify(error.body)}`)),
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Match.orElse(() => Console.log(`Unexpected HTTP error: ${error.status}`))
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Match.exhaustive // Forces handling all 400 | 500 - no escape hatch
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)),
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Effect.catchTag("TransportError", (error) =>
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Console.log(`Transport error: ${error.error.message}`))

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