Package com.jnape.palatable.lambda.monad
Class SafeT<M extends MonadRec<?,M>,A>
- java.lang.Object
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- com.jnape.palatable.lambda.monad.SafeT<M,A>
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- Type Parameters:
M
- theMonadRec
instanceA
- the carrier type
- All Implemented Interfaces:
Applicative<A,SafeT<M,?>>
,Functor<A,SafeT<M,?>>
,Monad<A,SafeT<M,?>>
,MonadBase<M,A,SafeT<?,?>>
,MonadRec<A,SafeT<M,?>>
,MonadT<M,A,SafeT<M,?>,SafeT<?,?>>
public final class SafeT<M extends MonadRec<?,M>,A> extends java.lang.Object implements MonadT<M,A,SafeT<M,?>,SafeT<?,?>>
A stack-safemonad transformer
that can safely interpret deeply nested left- or right-associated binds for anyMonadRec
.Example:
Times.<Fn1<Integer, Integer>>times(100_000, f -> f.fmap(x -> x + 1), id()).apply(0); // stack-overflow Times.<SafeT<Fn1<Integer, ?>, Integer>>times(100_000, f -> f.fmap(x -> x + 1), safeT(id())) .<Fn1<Integer, Integer>>runSafeT() .apply(0); // 100_000
Inspired by Phil Freeman's paper Stack Safety for Free.
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Nested Class Summary
Nested Classes Modifier and Type Class Description private static class
SafeT.Body<M extends MonadRec<?,M>,A>
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description <B> SafeT<M,B>
discardL(Applicative<B,SafeT<M,?>> appB)
Sequence both thisApplicative
andappB
, discarding thisApplicative's
result and returningappB
.<B> SafeT<M,A>
discardR(Applicative<B,SafeT<M,?>> appB)
Sequence both thisApplicative
andappB
, discardingappB's
result and returning thisApplicative
.<B> SafeT<M,B>
flatMap(Fn1<? super A,? extends Monad<B,SafeT<M,?>>> f)
Chain dependent computations that may continue or short-circuit based on previous results.<B> SafeT<M,B>
fmap(Fn1<? super A,? extends B> fn)
Covariantly transmute this functor's parameter using the given mapping function.<B> Lazy<SafeT<M,B>>
lazyZip(Lazy<? extends Applicative<Fn1<? super A,? extends B>,SafeT<M,?>>> lazyAppFn)
Given alazy
instance of this applicative over a mapping function, "zip" the two instances together using whatever application semantics the current applicative supports.<B,N extends MonadRec<?,N>>
SafeT<N,B>lift(MonadRec<B,N> nb)
static Lift<SafeT<?,?>>
liftSafeT()
<B> SafeT<M,B>
pure(B b)
Lift the valueb
into this applicative functor.static <M extends MonadRec<?,M>>
Pure<SafeT<M,?>>pureSafeT(Pure<M> pureM)
<MA extends MonadRec<A,M>>
MArunSafeT()
Recover the full structure of the embeddedMonad
in a stack-safe way.static <M extends MonadRec<?,M>,A>
SafeT<M,A>safeT(MonadRec<A,M> ma)
<B> SafeT<M,B>
trampolineM(Fn1<? super A,? extends MonadRec<RecursiveResult<A,B>,SafeT<M,?>>> bounce)
Given some operation yielding aRecursiveResult
inside thisMonadRec
, internally trampoline the operation until it yields atermination
instruction.<B> SafeT<M,B>
zip(Applicative<Fn1<? super A,? extends B>,SafeT<M,?>> appFn)
Given another instance of this applicative over a mapping function, "zip" the two instances together using whatever application semantics the current applicative supports.
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Constructor Detail
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SafeT
private SafeT(SafeT.Body<M,A> body, Pure<M> pureM)
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Method Detail
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runSafeT
public <MA extends MonadRec<A,M>> MA runSafeT()
Recover the full structure of the embeddedMonad
in a stack-safe way.- Type Parameters:
MA
- the witnessed target type- Returns:
- the embedded
Monad
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fmap
public <B> SafeT<M,B> fmap(Fn1<? super A,? extends B> fn)
Covariantly transmute this functor's parameter using the given mapping function. Generally this method is specialized to return an instance of the class implementing Functor.- Specified by:
fmap
in interfaceApplicative<M extends MonadRec<?,M>,A>
- Specified by:
fmap
in interfaceFunctor<M extends MonadRec<?,M>,A>
- Specified by:
fmap
in interfaceMonad<M extends MonadRec<?,M>,A>
- Specified by:
fmap
in interfaceMonadRec<M extends MonadRec<?,M>,A>
- Specified by:
fmap
in interfaceMonadT<M extends MonadRec<?,M>,A,SafeT<M extends MonadRec<?,M>,?>,SafeT<?,?>>
- Type Parameters:
B
- the new parameter type- Parameters:
fn
- the mapping function- Returns:
- a functor over B (the new parameter type)
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lift
public <B,N extends MonadRec<?,N>> SafeT<N,B> lift(MonadRec<B,N> nb)
- Specified by:
lift
in interfaceMonadBase<M extends MonadRec<?,M>,A,SafeT<?,?>>
- Specified by:
lift
in interfaceMonadT<M extends MonadRec<?,M>,A,SafeT<M extends MonadRec<?,M>,?>,SafeT<?,?>>
- Type Parameters:
B
- theMonadRec
carrier typeN
- the argumentMonadRec
witness- Parameters:
nb
- the argumentMonadRec
- Returns:
- the new
MonadBase
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flatMap
public <B> SafeT<M,B> flatMap(Fn1<? super A,? extends Monad<B,SafeT<M,?>>> f)
Chain dependent computations that may continue or short-circuit based on previous results.- Specified by:
flatMap
in interfaceMonad<M extends MonadRec<?,M>,A>
- Specified by:
flatMap
in interfaceMonadRec<M extends MonadRec<?,M>,A>
- Specified by:
flatMap
in interfaceMonadT<M extends MonadRec<?,M>,A,SafeT<M extends MonadRec<?,M>,?>,SafeT<?,?>>
- Type Parameters:
B
- the resulting monad parameter type- Parameters:
f
- the dependent computation over A- Returns:
- the new monad instance
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zip
public <B> SafeT<M,B> zip(Applicative<Fn1<? super A,? extends B>,SafeT<M,?>> appFn)
Given another instance of this applicative over a mapping function, "zip" the two instances together using whatever application semantics the current applicative supports.- Specified by:
zip
in interfaceApplicative<M extends MonadRec<?,M>,A>
- Specified by:
zip
in interfaceMonad<M extends MonadRec<?,M>,A>
- Specified by:
zip
in interfaceMonadRec<M extends MonadRec<?,M>,A>
- Specified by:
zip
in interfaceMonadT<M extends MonadRec<?,M>,A,SafeT<M extends MonadRec<?,M>,?>,SafeT<?,?>>
- Type Parameters:
B
- the resulting applicative parameter type- Parameters:
appFn
- the other applicative instance- Returns:
- the mapped applicative
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lazyZip
public <B> Lazy<SafeT<M,B>> lazyZip(Lazy<? extends Applicative<Fn1<? super A,? extends B>,SafeT<M,?>>> lazyAppFn)
Given alazy
instance of this applicative over a mapping function, "zip" the two instances together using whatever application semantics the current applicative supports. This is useful for applicatives that support lazy evaluation and early termination.- Specified by:
lazyZip
in interfaceApplicative<M extends MonadRec<?,M>,A>
- Specified by:
lazyZip
in interfaceMonad<M extends MonadRec<?,M>,A>
- Specified by:
lazyZip
in interfaceMonadRec<M extends MonadRec<?,M>,A>
- Specified by:
lazyZip
in interfaceMonadT<M extends MonadRec<?,M>,A,SafeT<M extends MonadRec<?,M>,?>,SafeT<?,?>>
- Type Parameters:
B
- the resulting applicative parameter type- Parameters:
lazyAppFn
- the lazy other applicative instance- Returns:
- the mapped applicative
- See Also:
Maybe
,Either
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discardL
public <B> SafeT<M,B> discardL(Applicative<B,SafeT<M,?>> appB)
Sequence both thisApplicative
andappB
, discarding thisApplicative's
result and returningappB
. This is generally useful for sequentially performing side-effects.- Specified by:
discardL
in interfaceApplicative<M extends MonadRec<?,M>,A>
- Specified by:
discardL
in interfaceMonad<M extends MonadRec<?,M>,A>
- Specified by:
discardL
in interfaceMonadRec<M extends MonadRec<?,M>,A>
- Specified by:
discardL
in interfaceMonadT<M extends MonadRec<?,M>,A,SafeT<M extends MonadRec<?,M>,?>,SafeT<?,?>>
- Type Parameters:
B
- the type of the returned Applicative's parameter- Parameters:
appB
- the other Applicative- Returns:
- appB
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discardR
public <B> SafeT<M,A> discardR(Applicative<B,SafeT<M,?>> appB)
Sequence both thisApplicative
andappB
, discardingappB's
result and returning thisApplicative
. This is generally useful for sequentially performing side-effects.- Specified by:
discardR
in interfaceApplicative<M extends MonadRec<?,M>,A>
- Specified by:
discardR
in interfaceMonad<M extends MonadRec<?,M>,A>
- Specified by:
discardR
in interfaceMonadRec<M extends MonadRec<?,M>,A>
- Specified by:
discardR
in interfaceMonadT<M extends MonadRec<?,M>,A,SafeT<M extends MonadRec<?,M>,?>,SafeT<?,?>>
- Type Parameters:
B
- the type of appB's parameter- Parameters:
appB
- the other Applicative- Returns:
- this Applicative
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pure
public <B> SafeT<M,B> pure(B b)
Lift the valueb
into this applicative functor.- Specified by:
pure
in interfaceApplicative<M extends MonadRec<?,M>,A>
- Specified by:
pure
in interfaceMonad<M extends MonadRec<?,M>,A>
- Specified by:
pure
in interfaceMonadRec<M extends MonadRec<?,M>,A>
- Specified by:
pure
in interfaceMonadT<M extends MonadRec<?,M>,A,SafeT<M extends MonadRec<?,M>,?>,SafeT<?,?>>
- Type Parameters:
B
- the type of the returned applicative's parameter- Parameters:
b
- the value- Returns:
- an instance of this applicative over b
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trampolineM
public <B> SafeT<M,B> trampolineM(Fn1<? super A,? extends MonadRec<RecursiveResult<A,B>,SafeT<M,?>>> bounce)
Given some operation yielding aRecursiveResult
inside thisMonadRec
, internally trampoline the operation until it yields atermination
instruction.Stack-safety depends on implementations guaranteeing that the growth of the call stack is a constant factor independent of the number of invocations of the operation. For various examples of how this can be achieved in stereotypical circumstances, see the referenced types.
- Specified by:
trampolineM
in interfaceMonadRec<M extends MonadRec<?,M>,A>
- Type Parameters:
B
- the ultimate resulting carrier type- Parameters:
bounce
- the function to internally trampoline- Returns:
- the trampolined
MonadRec
- See Also:
for a basic implementation
,for a implementation
,for an implementation leveraging an already stack-safe
,for a implementation
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