Safe Haskell | Safe |
---|---|
Language | Haskell2010 |
A vague analog of free monads for invariant monoidals. This can provide a simple basis for things like invertible parsers.
- data Free f a where
- showsFree :: (forall a'. f a' -> ShowS) -> Free f a -> ShowS
- mapFree :: (forall a'. f a' -> m a') -> Free f a -> Free m a
- foldFree :: Monoid b => (forall a'. f a' -> a' -> b) -> Free f a -> a -> b
- produceFree :: Alternative m => (forall a'. f a' -> a' -> b) -> Free f a -> a -> m b
- runFree :: Alternative f => Free f a -> f a
- parseFree :: MonadPlus m => (forall a'. f a' -> b -> m a') -> Free f a -> [b] -> m (a, [b])
- reverseFree :: Free f a -> Free f a
- freeTNF :: Free f a -> Free f a
- freeTDNF :: Free f a -> Free f a
- sortFreeTDNF :: (forall a' b'. f a' -> f b' -> Ordering) -> Free f a -> Free f a
Documentation
Produce a MonoidalAlt
out of any type constructor, simply by converting each monoidal operation into a constructor.
Although a version more analogous to a free monad could be defined for instances of Functor
and restricted to Monoidal
, including the Yoneda transform makes this the more general case.
showsFree :: (forall a'. f a' -> ShowS) -> Free f a -> ShowS Source #
Construct a string representation of a Free
structure, given a way to show any f a
.
mapFree :: (forall a'. f a' -> m a') -> Free f a -> Free m a Source #
Transform the type constructor within a Free
.
produceFree :: Alternative m => (forall a'. f a' -> a' -> b) -> Free f a -> a -> m b Source #
foldFree
over Alternative rather than Monoid.
runFree :: Alternative f => Free f a -> f a Source #
Evaluate a Free
into an underlying Alternative
, by evaluating >|<
with <|>
.
parseFree :: MonadPlus m => (forall a'. f a' -> b -> m a') -> Free f a -> [b] -> m (a, [b]) Source #
Given a way to convert b
elements into any f a
, use a Free
to parse a list of b
elements into a value.
This just uses unconsState
with runFree
, and is the inverse of produceFree
, provided the given conversions are themselves inverses.
reverseFree :: Free f a -> Free f a Source #
freeTDNF :: Free f a -> Free f a Source #
Convert a Free
to Transform Disjunctive Normal Form: reorder the terms so thet at most one Transform
is on the outside, followed by Choose
terms, which are above all Join
terms', with Empty
and Free
as leaves.
Since each Join
above a Choose
creates a duplicate Join
term, the complexity and result size can be exponential (just as with boolean logic DNF).