ListT is:module

ListT done right, see https://www.haskell.org/haskellwiki/ListT_done_right_alternative There is also the list-t package on hackage (Nikita Volkov) but it again depends on other packages we do not use yet, so we rather implement the few bits we need afresh.

A list monad transformer / a monadic list. Monadic list example: A program which reads numbers from the user and accumulates them.

import Control.Monad.ListT.Funcs (repeatM)
import Data.List.Class (execute, scanl, takeWhile, mapL)
import Prelude hiding (scanl, takeWhile)

main =
execute . mapL print .
scanl (+) 0 .
fmap (fst . head) .
takeWhile (not . null) .
fmap reads $ repeatM getLine

Note: The transformers package also has a ListT type, which oddly enough it is not a list monad transformer. This module was deliberately named differently from transformers's module.

Monadic directory tree.

-- List of files under "." or subfolders with ".markdown" extension,
-- except for those with a name starting with "_" somewhere in their path. (like "_cache/index.markdown")
markdownFiles :: ListT IO FilePath
markdownFiles
= filter ((== ".markdown") . takeExtension) -- only take files with a ".markdown" extension
. lastL                                     -- get the leaves of the tree (files, not directories)
. scanl1 appendPath                         -- transform tree nodes to filenames including path
. prune (not . isPrefixOf "_")              -- ignore directories or files whose name starts with "_"
$ directoryTree "."                         -- directory tree starting at "."

Module name System.Directory.Tree is a better fit but it is taken by "directory-tree", a read-directory-tree-in-bulk module.

Retrieves the list of apps trusted by the admin of the logged in user. See: Admin Directory API Reference for directory.resolvedAppAccessSettings.ListTrustedApps.

Retrieves a list of transactions for a disbursement from your Merchant Center account. See: Content API for Shopping Reference for content.orderreports.listtransactions.