% Lazy NonDeterministic Lists
% Sebastian Fischer (sebf@informatik.unikiel.de)
This module provides nondeterministic lists.
>
>
> module Data.LazyNondet.List where
>
> import Data.Data
> import Data.LazyNondet
> import Data.LazyNondet.Bool
>
> import Control.Monad.Constraint
>
> instance ConsRep [()] where consRep = toConstr
>
> nil :: Monad m => Nondet m [a]
> nil = cons ([] :: [()])
>
> pNil :: (cs -> Nondet m a) -> Match cs m a
> pNil = match ([] :: [()])
>
> infixr 5 ^:
> (^:) :: Monad m => Nondet m a -> Nondet m [a] -> Nondet m [a]
> (^:) = cons ((:) :: () -> [()] -> [()])
>
> pCons :: (cs -> Nondet m a -> Nondet m [a] -> Nondet m b) -> Match cs m b
> pCons = match ((:) :: () -> [()] -> [()])
>
> fromList :: Monad m => [Nondet m a] -> Nondet m [a]
> fromList = foldr (^:) nil
We can use logic variables of a list type if there are logic variables
for the element type.
> instance Unknown a => Unknown [a]
> where
> unknown = withUnique $ \u1 u2 ->
> oneOf [nil, unknown u1 ^: unknown u2]
Some operations on lists:
> null :: MonadSolve cs m m => Nondet m [a] -> cs -> Nondet m Bool
> null xs = caseOf_ xs [pNil (\_ -> true)] false
>
> head :: MonadSolve cs m m => Nondet m [a] -> cs -> Nondet m a
> head l = caseOf l [pCons (\_ x _ -> x)]
>
> tail :: MonadSolve cs m m => Nondet m [a] -> cs -> Nondet m [a]
> tail l = caseOf l [pCons (\_ _ xs -> xs)]