#5 Add unproven function for programmatic injection

src/index.ts

@@ -1,6 +1,28 @@
 import { readFileSync } from "fs"
-import { main } from "./main"
+import { assigner, main, Reader } from "./main"
+
+const {assign: $assign} = Object
+
 export { parse } from "./parse"
+export { argEnv }
+export default argEnv
+
+/**
+ * **NB!** args, package and ENV are already picked
+ * Revert precedence
+ * @param {string[]} paths
+ * @param {*} [env] `= process.env`
+ * @param {*} [target] `= {}`
+ * @param {*} [reader] `= readFileSync`
+ */
+// TODO #4 Like `path.unshift(".env")`
+// TODO Move to a separate module
+function argEnv<T extends Record<string, unknown>>(paths: string[], env = process.env, target = {} as T, reader = readFileSync as Reader) {
+  assigner(env, paths, reader, target)
+  $assign(env, target)
+
+  return target
+}
 
 main(
   process.env,

src/main.ts

@@ -53,6 +53,7 @@ function assigner(
   const {length} = files
 
   for (let i = length; i--; )
+    // NB commutative
     $assign(
       envPatch,
       parse(