Multiarg.Examples.Grover

Grover is a simple example program that shows how to write a parser for commands with multiple modes. You build such parsers using Multiarg.Mode. It provides an example for the documentation, and it also provides fodder for the QuickCheck tests. You will want to look at the source code.

Grover has three modes: int, string, and maybe. Each of these modes has three options: -z or --zero, which takes no arguments; -s or --single, which takes one argument; -d or --double, which takes two arguments; and -t or --triple, which takes three arguments. The type of the argument depends on the mode. For int, the argument or arguments must be an integer; for string the arguments can be any string; and for maybe the arguments must be a Maybe Int, such as Nothing or Just 5.

Each mode also accepts any number of positional arguments, which can be any string.

Grover handles simple errors right inside the parser by using the Either type as a return value.

Documentation

data Global

Grover's global options.

Constructors

Help

Verbose Int

The Int would indicate, for example, the desired level of verbosity.

Version

Instances

Eq Global

Ord Global

Show Global

data GroverOpt a

Handles all options and positional arguments for any Grover mode.

Constructors

Zero

Single a

Double a a

Triple a a a

PosArg String

Instances

Functor GroverOpt

Eq a => Eq (GroverOpt a)

Ord a => Ord (GroverOpt a)

Show a => Show (GroverOpt a)

globalOptSpecs :: [OptSpec (Either String Global)]

All of Grover's global options. The OptSpec is parameterized on an Either to allow for error handling. If the user enters a non-integer argument for the --verbose option, a Left with an error message is returned.

modeOptSpecs :: Read a => [OptSpec (Either String (GroverOpt a))]

A list of OptSpec that works for any Mode.

data Result

Holds the results of parsing Grover's modes.

Constructors

Ints [Either String (GroverOpt Int)]

Strings [Either String (GroverOpt String)]

Maybes [Either String (GroverOpt (Maybe Int))]

Instances

Eq Result

Ord Result

Show Result

modes :: [Mode Result]

All Grover modes.

readErr :: Read a => String -> Either String a

Reads a value. If it cannot be read, returns an error message.

parseGrover

Arguments

:: [String]

Command line arguments, presumably from getArgs

-> Either (String, [String]) (ModeResult (Either String Global) Result)

Returns a Left if there are errors, or a Right if there are no errors. (In an actual application, further processing of a Right would be necessary to determine whether all entered arguments were valid.)

Parses all of Grover's options and modes.