Make defaultListPrefix() a generator

README.md

@@ -48,7 +48,7 @@ for await (const dependency of traverse(new URL('file:///directory/file.js'), re
 
 #### `const dependencies = traverse(url[, options], readModule[, listPrefix])`
 
-Traverse the module graph rooted at `url`, which must be a WHATWG `URL` instance. `readModule` is called with a `URL` instance for every module to be read and must either return the module source, if it exists, or `null`. `listPrefix` is called with a `URL` instance of every prefix to be listed and must return a list of `URL` instances that have the specified `URL` as a prefix. If not provided, prefixes won't be traversed. If `readModule` returns a promise or `listPrefix` returns a promise generator, synchronous iteration is not supported.
+Traverse the module graph rooted at `url`, which must be a WHATWG `URL` instance. `readModule` is called with a `URL` instance for every module to be read and must either return the module source, if it exists, or `null`. `listPrefix` is called with a `URL` instance of every prefix to be listed and must yield `URL` instances that have the specified `URL` as a prefix. If not provided, prefixes won't be traversed. If `readModule` returns a promise or `listPrefix` returns a promise generator, synchronous iteration is not supported.
 
 Options include:
 

index.js

@@ -88,9 +88,7 @@ module.exports = exports = function traverse (entry, opts, readModule, listPrefi
   }
 }
 
-function defaultListPrefix () {
-  return []
-}
+function * defaultListPrefix () {}
 
 function addURL (array, url) {
   let lo = 0