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This is a library of interactive processes combinators, usable to define extensible keymaps.

(Inspired by the Parsec library, written by Koen Claessen)

The processes are:

  • composable: in parallel using <|>, in sequence using monadic bind.
  • extensible: it is always possible to override a behaviour by combination of adjustPriority and <|>. (See also <|| for a convenient combination of the two.)
  • monadic: sequencing is done via monadic bind. (leveraging the whole battery of monadic tools that Haskell provides)

The processes can parse input, and write output that depends on it.

The semantics are quite obvious; only disjunction deserve a bit more explanation:

in p = (a <|> b), what happens if a and b recognize the same input (prefix), but produce conflicting output?

  • if the output is the same (as by the PEq class), then the processes (prefixes) are merged * if a Write is more prioritized than the other, the one with low priority will be discarded * otherwise, the output will be delayed until one of the branches can be discarded. * if there is no way to disambiguate, then no output will be generated anymore. This situation can be detected by using possibleActions however.



data I ev w a Source

Interactive process description


Monad (I event w) 
Functor (I event w) 
PEq w => MonadPlus (I event w) 
Applicative (I ev w) 
Alternative (I ev w) 
PEq w => MonadInteract (I event w) w event 

data P event w Source

Operational representation of a process


forall mid . (Show mid, PEq mid) => Chain (P event mid) (P mid w) 


(Show w, Show ev) => Show (P ev w) 

data InteractState event w Source

Abstraction of the automaton state.


Ambiguous [(Int, w, P event w)] 
Running w (P event w) 


Monoid (InteractState event w) 

class (PEq w, Monad m, Alternative m, Applicative m, MonadPlus m) => MonadInteract m w e | m -> w e whereSource

Abstraction of monadic interactive processes


write :: w -> m ()Source

Outputs a result.

eventBounds :: Ord e => Maybe e -> Maybe e -> m eSource

Consumes and returns the next character. Fails if there is no input left, or outside the given bounds.

adjustPriority :: Int -> m ()Source


MonadInteract m w e => MonadInteract (StateT s m) w e 
PEq w => MonadInteract (I event w) w event 

class PEq a whereSource


equiv :: a -> a -> BoolSource


(<||), (||>) :: MonadInteract f w e => f a -> f a -> f aSource

option :: MonadInteract m w e => a -> m a -> m aSource

option x p will either parse p or return x without consuming any input.

oneOf :: (Ord event, MonadInteract m w event) => [event] -> m eventSource

processOneEvent :: PEq w => P event w -> event -> ([w], P event w)Source

computeState :: PEq w => P event w -> InteractState event wSource

event :: (Ord event, MonadInteract m w event) => event -> m eventSource

Parses and returns the specified character.

events :: (Ord event, MonadInteract m w event) => [event] -> m [event]Source

Parses and returns the specified list of events (lazily).

choice :: MonadInteract m w e => [m a] -> m aSource

Combines all parsers in the specified list.

mkAutomaton :: PEq w => I ev w a -> P ev wSource

idAutomaton :: (Ord a, PEq a) => P a aSource

runWrite :: PEq w => P event w -> [event] -> [w]Source

anyEvent :: (Ord event, MonadInteract m w event) => m eventSource

eventBetween :: (Ord e, MonadInteract m w e) => e -> e -> m eSource

accepted :: Show ev => Int -> P ev w -> [[String]]Source