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Functional Java is an open source library that supports closures for the Java programming language
package fj;
import fj.data.Option;
/**
* Transformations on functions.
*
* @version %build.number%
*/
public final class Function {
private Function() {
throw new UnsupportedOperationException();
}
/**
* Function application with the arguments flipped.
*
* @param a The value to apply the function to.
* @return A function that is partially-applied to the given value.
*/
public static F, B> apply(final A a) {
return f -> f.f(a);
}
/**
* Function composition.
*
* @return A function that composes two functions to produce a new function.
*/
public static F, F, F>> compose() {
return f -> g -> compose(f, g);
}
/**
* Function composition.
*
* @param f A function to compose with another.
* @param g A function to compose with another.
* @return A function that is the composition of the given arguments.
*/
public static F compose(final F f, final F g) {
return a -> f.f(g.f(a));
}
/**
* Function composition.
*
* @param f A function to compose with another.
* @param g A function to compose with another.
* @return A function that is the composition of the given arguments.
*/
public static F> compose2(final F f, final F> g) {
return a -> b -> f.f(g.f(a).f(b));
}
/**
* Function composition flipped.
*
* @return A function that composes two functions to produce a new function.
*/
public static F, F, F>> andThen() {
return g -> f -> andThen(g, f);
}
/**
* Function composition flipped.
*
* @param g A function to compose with another.
* @param f A function to compose with another.
* @return A function that is the composition of the given arguments.
*/
public static F andThen(final F g, final F f) {
return a -> f.f(g.f(a));
}
/**
* The identity transformation.
*
* @return The identity transformation.
*/
public static F identity() {
return a -> a;
}
/**
* Returns a function that given an argument, returns a function that ignores its argument.
*
* @return A function that given an argument, returns a function that ignores its argument.
*/
public static F> constant() {
return Function::constant;
}
/**
* Returns a function that ignores its argument to constantly produce the given value.
*
* @param b The value to return when the returned function is applied.
* @return A function that ignores its argument to constantly produce the given value.
*/
public static F constant(final B b) {
return a -> b;
}
/**
* Simultaneously covaries and contravaries a function.
*
* @param f The function to vary.
* @return A co- and contravariant function that invokes f on its argument.
*/
public static F vary(final F f) {
return f::f;
}
/**
* Simultaneously covaries and contravaries a function.
*
* @return A function that varies and covaries a function.
*/
public static F, F> vary() {
return Function::vary;
}
/**
* Function argument flipping.
*
* @return A function that takes a function and flips its arguments.
*/
public static F>, F>> flip() {
return Function::flip;
}
/**
* Function argument flipping.
*
* @param f The function to flip.
* @return The given function flipped.
*/
public static F> flip(final F> f) {
return b -> a -> f.f(a).f(b);
}
/**
* Function argument flipping.
*
* @param f The function to flip.
* @return The given function flipped.
*/
public static F2 flip(final F2 f) {
return (b, a) -> f.f(a, b);
}
/**
* Function argument flipping.
*
* @return A function that flips the arguments of a given function.
*/
public static F, F2> flip2() {
return Function::flip;
}
/**
* Return a function that inspects the argument of the given function for a null value and if so, does
* not apply the value, instead returning an empty optional value.
*
* @param f The function to check for a null argument.
* @return A function that inspects the argument of the given function for a null value and if so, does
* not apply the value, instead returning an empty optional value.
*/
public static F> nullable(final F f) {
return a -> a == null ? Option.none() : Option.some(f.f(a));
}
/**
* Curry a function of arity-2.
*
* @param f The function to curry.
* @return A curried form of the given function.
*/
public static F> curry(final F2 f) {
return a -> b -> f.f(a, b);
}
/**
* Curry a function of arity-2.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @return A curried form of the given function.
*/
public static F curry(final F2 f, final A a) {
return curry(f).f(a);
}
/**
* Uncurry a function of arity-2.
*
* @return An uncurried function.
*/
public static F>, F2> uncurryF2() {
return Function::uncurryF2;
}
/**
* Uncurry a function of arity-2.
*
* @param f The function to uncurry.
* @return An uncurried function.
*/
public static F2 uncurryF2(final F> f) {
return (a, b) -> f.f(a).f(b);
}
/**
* Curry a function of arity-3.
*
* @param f The function to curry.
* @return A curried form of the given function.
*/
public static F>> curry(final F3 f) {
return a -> b -> c -> f.f(a, b, c);
}
/**
* Curry a function of arity-3.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @return A curried form of the given function.
*/
public static F> curry(final F3 f, final A a) {
return curry(f).f(a);
}
/**
* Curry a function of arity-3.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @return A curried form of the given function.
*/
public static F curry(final F3 f, final A a, final B b) {
return curry(f, a).f(b);
}
/**
* Uncurry a function of arity-3.
*
* @return An uncurried function.
*/
public static F>>, F3> uncurryF3() {
return Function::uncurryF3;
}
/**
* Uncurry a function of arity-3.
*
* @param f The function to uncurry.
* @return An uncurried function.
*/
public static F3 uncurryF3(final F>> f) {
return (a, b, c) -> f.f(a).f(b).f(c);
}
/**
* Curry a function of arity-4.
*
* @param f The function to curry.
* @return A curried form of the given function.
*/
public static F>>> curry(final F4 f) {
return a -> b -> c -> d -> f.f(a, b, c, d);
}
/**
* Curry a function of arity-4.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>> curry(final F4 f, final A a) {
return curry(f).f(a);
}
/**
* Curry a function of arity-4.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @return A curried form of the given function.
*/
public static F> curry(final F4 f, final A a, final B b) {
return curry(f).f(a).f(b);
}
/**
* Curry a function of arity-4.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @return A curried form of the given function.
*/
public static F curry(final F4 f, final A a, final B b, final C c) {
return curry(f).f(a).f(b).f(c);
}
/**
* Uncurry a function of arity-4.
*
* @return An uncurried function.
*/
public static F>>>, F4> uncurryF4() {
return Function::uncurryF4;
}
/**
* Uncurry a function of arity-4.
*
* @param f The function to uncurry.
* @return An uncurried function.
*/
public static F4 uncurryF4(final F>>> f) {
return (a, b, c, d) -> f.f(a).f(b).f(c).f(d);
}
/**
* Curry a function of arity-5.
*
* @param f The function to curry.
* @return A curried form of the given function.
*/
public static F>>>> curry(final F5 f) {
return a -> b -> c -> d -> e -> f.f(a, b, c, d, e);
}
/**
* Curry a function of arity-5.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>>> curry(final F5 f, final A a) {
return curry(f).f(a);
}
/**
* Curry a function of arity-5.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>> curry(final F5 f, final A a, final B b) {
return curry(f).f(a).f(b);
}
/**
* Curry a function of arity-5.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @return A curried form of the given function.
*/
public static F> curry(final F5 f, final A a, final B b,
final C c) {
return curry(f).f(a).f(b).f(c);
}
/**
* Curry a function of arity-5.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @param d An argument to the curried function.
* @return A curried form of the given function.
*/
public static F curry(final F5 f, final A a, final B b, final C c,
final D d) {
return curry(f).f(a).f(b).f(c).f(d);
}
/**
* Uncurry a function of arity-5.
*
* @return An uncurried function.
*/
public static F>>>>, F5> uncurryF5() {
return Function::uncurryF5;
}
/**
* Uncurry a function of arity-6.
*
* @param f The function to uncurry.
* @return An uncurried function.
*/
public static F5 uncurryF5(final F>>>> f) {
return (a, b, c, d, e) -> f.f(a).f(b).f(c).f(d).f(e);
}
/**
* Curry a function of arity-6.
*
* @param f The function to curry.
* @return A curried form of the given function.
*/
public static F>>>>> curry(final F6 f) {
return a -> b -> c -> d -> e -> f$ -> f.f(a, b, c, d, e, f$);
}
/**
* Uncurry a function of arity-6.
*
* @return An uncurried function.
*/
public static F>>>>>, F6> uncurryF6() {
return Function::uncurryF6;
}
/**
* Uncurry a function of arity-6.
*
* @param f The function to uncurry.
* @return An uncurried function.
*/
public static F6 uncurryF6(
final F>>>>> f) {
return (a, b, c, d, e, f$) -> f.f(a).f(b).f(c).f(d).f(e).f(f$);
}
/**
* Curry a function of arity-7.
*
* @param f The function to curry.
* @return A curried form of the given function.
*/
public static F>>>>>> curry(
final F7 f) {
return a -> b -> c -> d -> e -> f$ -> g -> f.f(a, b, c, d, e, f$, g);
}
/**
* Curry a function of arity-7.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>>>>> curry(
final F7 f, final A a) {
return curry(f).f(a);
}
/**
* Curry a function of arity-7.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>>>> curry(final F7 f,
final A a, final B b) {
return curry(f).f(a).f(b);
}
/**
* Curry a function of arity-7.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>>> curry(final F7 f,
final A a, final B b, final C c) {
return curry(f).f(a).f(b).f(c);
}
/**
* Curry a function of arity-7.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @param d An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>> curry(final F7 f, final A a,
final B b, final C c, final D d) {
return curry(f).f(a).f(b).f(c).f(d);
}
/**
* Curry a function of arity-7.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @param d An argument to the curried function.
* @param e An argument to the curried function.
* @return A curried form of the given function.
*/
public static F> curry(final F7 f, final A a,
final B b, final C c, final D d, final E e) {
return curry(f).f(a).f(b).f(c).f(d).f(e);
}
/**
* Curry a function of arity-7.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @param d An argument to the curried function.
* @param e An argument to the curried function.
* @param f$ An argument to the curried function.
* @return A curried form of the given function.
*/
public static F curry(final F7 f, final A a, final B b,
final C c, final D d, final E e, final F$ f$) {
return curry(f).f(a).f(b).f(c).f(d).f(e).f(f$);
}
/**
* Uncurry a function of arity-7.
*
* @return An uncurried function.
*/
public static F>>>>>>, F7> uncurryF7() {
return Function::uncurryF7;
}
/**
* Uncurry a function of arity-7.
*
* @param f The function to uncurry.
* @return An uncurried function.
*/
public static F7 uncurryF7(
final F>>>>>> f) {
return (a, b, c, d, e, f$, g) -> f.f(a).f(b).f(c).f(d).f(e).f(f$).f(g);
}
/**
* Curry a function of arity-8.
*
* @param f The function to curry.
* @return A curried form of the given function.
*/
public static F>>>>>>> curry(
final F8 f) {
return a -> b -> c -> d -> e -> f$ -> g -> h -> f.f(a, b, c, d, e, f$, g, h);
}
/**
* Curry a function of arity-8.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>>>>>> curry(
final F8 f, final A a) {
return curry(f).f(a);
}
/**
* Curry a function of arity-8.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>>>>> curry(
final F8 f, final A a, final B b) {
return curry(f).f(a).f(b);
}
/**
* Curry a function of arity-8.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>>>> curry(
final F8 f, final A a, final B b, final C c) {
return curry(f).f(a).f(b).f(c);
}
/**
* Curry a function of arity-8.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @param d An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>>> curry(final F8 f,
final A a, final B b, final C c,
final D d) {
return curry(f).f(a).f(b).f(c).f(d);
}
/**
* Curry a function of arity-8.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @param d An argument to the curried function.
* @param e An argument to the curried function.
* @return A curried form of the given function.
*/
public static F>> curry(final F8 f,
final A a, final B b, final C c, final D d,
final E e) {
return curry(f).f(a).f(b).f(c).f(d).f(e);
}
/**
* Curry a function of arity-8.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @param d An argument to the curried function.
* @param e An argument to the curried function.
* @param f$ An argument to the curried function.
* @return A curried form of the given function.
*/
public static F> curry(final F8 f, final A a,
final B b, final C c, final D d, final E e,
final F$ f$) {
return curry(f).f(a).f(b).f(c).f(d).f(e).f(f$);
}
/**
* Curry a function of arity-7.
*
* @param f The function to curry.
* @param a An argument to the curried function.
* @param b An argument to the curried function.
* @param c An argument to the curried function.
* @param d An argument to the curried function.
* @param e An argument to the curried function.
* @param f$ An argument to the curried function.
* @param g An argument to the curried function.
* @return A curried form of the given function.
*/
public static F curry(final F8 f, final A a, final B b,
final C c, final D d, final E e, final F$ f$, final G g) {
return curry(f).f(a).f(b).f(c).f(d).f(e).f(f$).f(g);
}
/**
* Uncurry a function of arity-8.
*
* @return An uncurried function.
*/
public static F>>>>>>>, F8> uncurryF8() {
return Function::uncurryF8;
}
/**
* Uncurry a function of arity-8.
*
* @param f The function to uncurry.
* @return An uncurried function.
*/
public static F8 uncurryF8(
final F>>>>>>> f) {
return (a, b, c, d, e, f$, g, h) -> f.f(a).f(b).f(c).f(d).f(e).f(f$).f(g).f(h);
}
/**
* Binds the function in the second argument to the function in the first argument.
*
* @param ma A function whose argument type is the same as the argument type of the return value.
* @param f A function whose argument type is the same as the return type of ma,
* and yields the return value.
* @return A function that chains the given functions together such that the result of applying
* ma to the argument is given to f, yielding a function
* that is applied to the argument again.
*/
public static F bind(final F ma, final F> f) {
return m -> f.f(ma.f(m)).f(m);
}
/**
* Performs function application within a higher-order function (applicative functor pattern).
*
* @param cab The higher-order function to apply a function to.
* @param ca A function to apply within a higher-order function.
* @return A new function after applying the given higher-order function to the given function.
*/
public static F apply(final F> cab, final F ca) {
return apply(uncurryF2(cab), ca);
}
/**
* Performs function application within a higher-order function (applicative functor pattern).
*
* @param cab The higher-order function to apply a function to.
* @param ca A function to apply within a higher-order function.
* @return A new function after applying the given higher-order function to the given function.
*/
public static F apply(final F2 cab, final F ca) {
return c -> cab.f(c, ca.f(c));
}
/**
* Binds the given function f to the values of the given functions, with a final join.
*
* @param ca A function to bind f function to.
* @param cb A function to bind f function to.
* @param f The bound function to be composed with ca and then applied with cb
* @return A new function after performing the composition, then application.
*/
public static F bind(final F ca, final F cb, final F> f) {
return apply(compose(f, ca), cb);
}
/**
* Applies a given function over the arguments of another function of arity-2.
*
* @param a The function whose arguments to apply another function over.
* @param f The function to apply over the arguments of another function.
* @return A function whose arguments are fed through function f, before being passed to function a.
*/
public static F> on(final F> a, final F f) {
return compose(compose(Function.andThen().f(f), a), f);
}
/**
* Promotes a function of arity-2 to a higher-order function.
*
* @param f The function to promote.
* @return A function of arity-2 promoted to compose with two functions.
*/
public static F, F, F>> lift(final F> f) {
return curry((ca, cb) -> bind(ca, cb, f));
}
/**
* Joins two arguments of a function of arity-2 into one argument, yielding a function of arity-1.
*
* @param f A function whose arguments to join.
* @return A function of arity-1 whose argument is substituted for both parameters of f.
*/
public static F join(final F> f) {
return bind(f, Function.identity());
}
/**
* Partial application of the second argument to the supplied function to get a function of type
* A -> C. Same as flip(f).f(b).
*
* @param f The function to partially apply.
* @param b The value to apply to the function.
* @return A new function based on f with its second argument applied.
*/
public static F partialApply2(final F> f, final B b) {
return a -> uncurryF2(f).f(a, b);
}
/**
* Partial application of the third argument to the supplied function to get a function of type
* A -> B -> D.
*
* @param f The function to partially apply.
* @param c The value to apply to the function.
* @return A new function based on f with its third argument applied.
*/
public static F> partialApply3(final F>> f, final C c) {
return a -> b -> uncurryF3(f).f(a, b, c);
}
/**
* Partial application of the fourth argument to the supplied function to get a function of type
* A -> B -> C -> E.
*
* @param f The function to partially apply.
* @param d The value to apply to the function.
* @return A new function based on f with its fourth argument applied.
*/
public static F>> partialApply4(final F>>> f, final D d) {
return a -> b -> c -> uncurryF4(f).f(a, b, c, d);
}
/**
* Partial application of the fifth argument to the supplied function to get a function of type
* A -> B -> C -> D -> F$.
*
* @param f The function to partially apply.
* @param e The value to apply to the function.
* @return A new function based on f with its fifth argument applied.
*/
public static F>>> partialApply5(final F>>>> f,
final E e) {
return a -> b -> c -> d -> uncurryF5(f).f(a, b, c, d, e);
}
/**
* Partial application of the sixth argument to the supplied function to get a function of type
* A -> B -> C -> D -> E -> G.
*
* @param f The function to partially apply.
* @param f$ The value to apply to the function.
* @return A new function based on f with its sixth argument applied.
*/
public static F>>>> partialApply6(
final F>>>>> f, final F$ f$) {
return a -> b -> c -> d -> e -> uncurryF6(f).f(a, b, c, d, e, f$);
}
/**
* Partial application of the seventh argument to the supplied function to get a function of type
* A -> B -> C -> D -> E -> F$ -> H.
*
* @param f The function to partially apply.
* @param g The value to apply to the function.
* @return A new function based on f with its seventh argument applied.
*/
public static F>>>>> partialApply7(
final F>>>>>> f, final G g) {
return a -> b -> c -> d -> e -> f$ -> uncurryF7(f).f(a, b, c, d, e, f$, g);
}
/**
* Partial application of the eigth argument to the supplied function to get a function of type
* A -> B -> C -> D -> E -> F$ -> G -> I.
*
* @param f The function to partially apply.
* @param h The value to apply to the function.
* @return A new function based on f with its eigth argument applied.
*/
public static F>>>>>> partialApply8(
final F>>>>>>> f, final H h) {
return a -> b -> c -> d -> e -> f$ -> g -> uncurryF8(f).f(a, b, c, d, e, f$, g, h);
}
}