System.Console.Wizard

Wizards

newtype Wizard backend a

A Wizard a is a conversation with the user that will result in a data type a, or may fail. A Wizard is made up of one or more "primitives" (see below), composed using the Applicative, Monad and Alternative instances. The Alternative instance is, as you might expect, a maybe-style cascade. If the first wizard fails, the next one is tried.

The Wizard constructor is exported here for use when developing backends, but it is better for end-users to simply pretend that Wizard is an opaque data type. Don't depend on this unless you have no other choice.

Wizards are, internally, just a maybe transformer over a prompt monad for each primitive action.

Constructors

Wizard (MaybeT (RecPrompt (WizardAction backend)) a)

Instances

Monad (Wizard backend)

Functor (Wizard backend)

MonadPlus (Wizard backend)

Applicative (Wizard backend)

Alternative (Wizard backend)

MonadIO (Wizard Haskeline)

MonadIO (Wizard BasicIO)

MonadPrompt (WizardAction s (RecPrompt (WizardAction s))) (Wizard s)

type PromptString = String

Primitives

Primitives are the basic building blocks for wizards. Use these functions to produce wizards that ask for input from the user, or output information.

line :: PromptString -> Wizard b String

Read one line of input from the user.

linePrewritten

Arguments

:: PromptString

-> String

Text to the left of the cursor

-> String

Text to the right of the cursor

-> Wizard b String

Read one line of input, with some default text already present, before and/or after the editing cursor. Backends are not required to display this default text, or position the cursor anywhere, it is merely a suggestion.

password

Arguments

:: PromptString

-> Maybe Char

Mask character, if any.

-> Wizard b String

Read one line of password input, with an optional mask character. The exact masking behavior of the password may vary from backend to backend. The masking character does not have to be honoured.

character :: PromptString -> Wizard b Char

Read a single character only from input.

output :: String -> Wizard b ()

Output a string, if the backend used supports output.

outputLn :: String -> Wizard b ()

Output a string followed by a newline, if the backend used supports such output.

Modifiers

Modifiers change the behaviour of existing wizards.

retry :: Wizard b a -> Wizard b a

Retry produces a wizard that will retry the entire conversation again if it fails. Conceptually, it could thought of as retry x = x <|> retry x, however it also prints a user-friendly error message in the event of failure.

retryMsg :: String -> Wizard b a -> Wizard b a

Same as retry, except the error message can be specified.

defaultTo :: Wizard b a -> a -> Wizard b a

x `defaultTo` y will return y if x fails, e.g parseRead line `defaultTo` 0.

parser :: (a -> Maybe c) -> Wizard b a -> Wizard b c

Like fmap, except the function may be partial (Nothing causes the wizard to fail).

validator :: (a -> Bool) -> Wizard b a -> Wizard b a

validator p w causes a wizard to fail if the output value does not satisfy the predicate p.

Convenience

nonEmpty :: Wizard b [a] -> Wizard b [a]

Simply validator (not . null), makes a wizard fail if it gets an empty string.

inRange :: Ord a => (a, a) -> Wizard b a -> Wizard b a

Makes a wizard fail if it gets an ordered quantity outside of the given range.

parseRead :: Read a => Wizard b String -> Wizard b a

Simply parser readP. Attaches a simple read parser to a Wizard.

Utility

liftMaybe :: Maybe a -> Wizard b a

Translate a maybe value into wizard success/failure.

ensure :: (a -> Bool) -> a -> Maybe a

Ensures that a maybe value satisfies a given predicate.

readP :: Read a => String -> Maybe a

A read-based parser for the parser modifier.