fj.data

Class Eval<A>

java.lang.Object

fj.data.Eval<A>

public abstract class Eval<A>
extends java.lang.Object

Eval is an abstraction over different models of evaluation. The data constructors:

• Now - the value is evaluated immediately.
• Later - the value is evaluated only once when it's requested (lazy evaluation).
• Always - the value is evaluated every time when it's requested.

Both Later and Always are lazy computations, while Now is eager.

Constructor Summary

Constructors

Constructor and Description
Eval()

Method Summary

Modifier and Type	Method and Description
static <A> Eval<A>	always(F0<A> a) Constructs a lazy evaluation without caching.
<B> Eval<B>	bind(F<A,Eval<B>> f) Transforms Eval into a Eval using the given function that directly produces Eval.
static <A> Eval<A>	defer(F0<Eval<A>> a) Constructs a lazy evaluation of an expression that produces Eval.
<B> Eval<B>	flatMap(F<A,Eval<B>> f) Alias for bind(F).
static <A> Eval<A>	later(F0<A> a) Constructs a lazy evaluation with caching.
<B> Eval<B>	map(F<A,B> f) Transforms Eval into a Eval using the given function.
static <A> Eval<A>	now(A a) Constructs an eager evaluation by wrapping the given value.
abstract A	value() Evaluates the computation and return its result.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Eval

public Eval()

Method Detail

now

public static <A> Eval<A> now(A a)

Constructs an eager evaluation by wrapping the given value.

Parameters:

a - the evaluated value.

Returns:

an eval with computed value.

later

public static <A> Eval<A> later(F0<A> a)

Constructs a lazy evaluation with caching.

Parameters:

a - the supplier that evaluates a value.

Returns:

a lazy evaluation.

always

public static <A> Eval<A> always(F0<A> a)

Constructs a lazy evaluation without caching.

Parameters:

a - the supplier that evaluates a value.

Returns:

a lazy evaluation.

defer

public static <A> Eval<A> defer(F0<Eval<A>> a)

Constructs a lazy evaluation of an expression that produces Eval. This operation is stack-safe and can be used for recursive computations.

Parameters:

a - the supplier that produces an Eval.

Returns:

a lazily evaluated nested evaluation.

value

public abstract A value()

Evaluates the computation and return its result. Depending on whether the current instance is lazy or eager the computation may or may not happen at this point.

Returns:

a result of this computation.

map

public final <B> Eval<B> map(F<A,B> f)

Transforms Eval into a Eval using the given function. Note: the computation of the given transformation is always lazy, even if it invoked for an eager Now instance. This computation is performed in O(1) stack space.

Parameters:

f - the transformation function.

Returns:

a transformed evaluation.

flatMap

public final <B> Eval<B> flatMap(F<A,Eval<B>> f)

Alias for bind(F).

bind

public final <B> Eval<B> bind(F<A,Eval<B>> f)

Transforms Eval into a Eval using the given function that directly produces Eval. Note: the computation of the given transformation is always lazy, even if it invoked for an eager Now instance. This computation is performed in O(1) stack space.

Parameters:

f - the transformation function.

Returns:

a transformed evaluation.