Implement suggestion

package.json

@@ -84,6 +84,7 @@
     "@vitejs/plugin-react": "^3.0.1",
     "@vitest/coverage-c8": "^0.27.0",
     "babel-plugin-annotate-pure-calls": "^0.4.0",
+    "change-case": "^4.1.2",
     "concurrently": "^7.6.0",
     "cpx": "^1.5.0",
     "docs-ts": "0.6.10",

src/Config/Provider.ts

@@ -106,6 +106,8 @@ export declare namespace ConfigProvider {
   export interface FromEnvConfig {
     readonly pathDelim: string
     readonly seqDelim: string
+    readonly conversion: (k: string) => string
+    readonly reverseConversion: (k: string) => string
   }
 }
 

src/internal/configProvider.ts

@@ -106,9 +106,19 @@ export const fromFlat = (flat: ConfigProvider.ConfigProvider.Flat): ConfigProvid
 export const fromEnv = (
   config: Partial<ConfigProvider.ConfigProvider.FromEnvConfig> = {}
 ): ConfigProvider.ConfigProvider => {
-  const { pathDelim, seqDelim } = Object.assign({}, { pathDelim: "_", seqDelim: "," }, config)
-  const makePathString = (path: Chunk.Chunk<string>): string => pipe(path, Chunk.join(pathDelim))
-  const unmakePathString = (pathString: string): ReadonlyArray<string> => pathString.split(pathDelim)
+  const { conversion, pathDelim, reverseConversion, seqDelim } = Object.assign(
+    {},
+    {
+      pathDelim: "_",
+      seqDelim: ",",
+      conversion: (k) => k,
+      reverseConversion: (k) => k
+    } as ConfigProvider.ConfigProvider.FromEnvConfig,
+    config
+  )
+  const makePathString = (path: Chunk.Chunk<string>): string => pipe(path, Chunk.map(conversion), Chunk.join(pathDelim))
+  const unmakePathString = (pathString: string): ReadonlyArray<string> =>
+    pathString.split(pathDelim).map(reverseConversion)
 
   const getEnv = () =>
     typeof process !== "undefined" && "env" in process && typeof process.env === "object" ? process.env : {}

test/ConfigProvider.ts

@@ -10,6 +10,10 @@ import * as HashMap from "@fp-ts/data/HashMap"
 import * as HashSet from "@fp-ts/data/HashSet"
 import { assert, describe } from "vitest"
 
+// TODO: Why?
+// @ts-expect-error
+import { camelCase, constantCase } from "change-case"
+
 interface HostPort {
   readonly host: string
   readonly port: number
@@ -324,13 +328,16 @@ describe.concurrent("ConfigProvider", () => {
     }))
 })
 
+const makeEnvProvider = () =>
+  ConfigProvider.fromEnv({ pathDelim: "__", conversion: constantCase, reverseConversion: camelCase, seqDelim: "," })
+
 describe.concurrent("EnvProvider", () => {
   it.effect("capitalisation", () => {
     return Effect.gen(function*($) {
       // current in comments
       process.env["HOST" /* "host" */] = "localhost"
       process.env["PORT" /* "port" */] = "8080"
-      const provider = ConfigProvider.fromEnv()
+      const provider = makeEnvProvider()
       const result = yield* $(provider.load(hostPortConfig))
       assert.deepStrictEqual(result, {
         host: "localhost",
@@ -345,7 +352,7 @@ describe.concurrent("EnvProvider", () => {
       process.env["HOST_PORT__HOST" /* "hostPort_host" */] = "localhost"
       process.env["HOST_PORT__PORT" /* "hostPort_port" */] = "8080"
       process.env["TIMEOUT" /* "timeout" */] = "1000"
-      const provider = ConfigProvider.fromEnv()
+      const provider = makeEnvProvider()
       const result = yield* $(provider.load(serviceConfigConfig))
       assert.deepStrictEqual(result, {
         hostPort: {
@@ -357,7 +364,7 @@ describe.concurrent("EnvProvider", () => {
     })
   })
 
-  it.effect("current - should fail", () => {
+  it.effect("default", () => {
     return Effect.gen(function*($) {
       process.env["hostPort_host"] = "localhost"
       process.env["hostPort_port"] = "8080"