Maybe add the default value and make sure it will be shown in help message.

Parser for path to a file where output will be writen.

Supporting typeclass for namedParser. It specifies how a value should be parsed from command line. Even though the main purpose of this class is to implement helpers below, feel free to use it for other goals.

Create a Parser for a value using HasCLReader instance (hence CL in the name). It uses reader and metavar from that class, the rest should be supplied as arguments.

We expect some common modifiers to be always provided, a list of extra modifies can be provided as well.

A more general version of mkCLOptionParser which takes a list of extra (not as widely used) modifiers.

Akin to mkCLOptionParser, but for arguments rather than options.

Akin to mkCLOptionParserExt, but for arguments rather than options.

Create a Parser for a value using its type-level name.

This expects type-level name to be in camelCase as appropriate for Haskell and transforms the variable inside.

Convert a function producing an Either into a reader.

As an example, one can create a ReadM from an attoparsec Parser easily with

import qualified Data.Attoparsec.Text as A
import qualified Data.Text as T
attoparsecReader :: A.Parser a -> ReadM a
attoparsecReader p = eitherReader (A.parseOnly p . T.pack)

Abort option reader by exiting with an error message.