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Paul Campbell 2018-07-16 19:07:19 +01:00
parent c7c7c6ebeb
commit 3e4629d873
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@ -1,7 +1,4 @@
* Mon
:PROPERTIES:
:CUSTOM_ID: mon
:END:
** TypeAlias, Maybe and Result for Java.
@ -23,10 +20,8 @@
[[https://app.codacy.com/project/kemitix/mon/dashboard][file:https://img.shields.io/codacy/grade/d57096b0639d496aba9a7e43e7cf5b4c.svg?style=for-the-badge]]
[[http://i.jpeek.org/net.kemitix/mon/index.html][file:http://i.jpeek.org/net.kemitix/mon/badge.svg]]
** Maven
:PROPERTIES:
:CUSTOM_ID: maven
:END:
#+BEGIN_SRC xml
<dependency>
@ -41,9 +36,6 @@
** TypeAlias
:PROPERTIES:
:CUSTOM_ID: typealias
:END:
In Haskell it is possible to create an alias for a Type, and to then use
that alias with the same behaviour as the original, except that the compiler
@ -127,10 +119,8 @@
}
#+END_SRC
** Maybe
:PROPERTIES:
:CUSTOM_ID: maybe
:END:
Allows specifying that a value may or may not be present. Similar to
=Optional=. =Maybe= provides additional methods that =Optional= doesn't:
@ -180,218 +170,232 @@
=nothing= drops straight through the map and triggers the Runnable parameter
in the =match= call.
**** =Maybe= is a Monad:
*** =Maybe= is a Monad:
#+BEGIN_SRC java
package net.kemitix.mon;
#+BEGIN_SRC java
package net.kemitix.mon;
import net.kemitix.mon.maybe.Maybe;
import org.assertj.core.api.WithAssertions;
import org.junit.Test;
import net.kemitix.mon.maybe.Maybe;
import org.assertj.core.api.WithAssertions;
import org.junit.Test;
import java.util.function.Function;
import java.util.function.Function;
public class MaybeMonadTest implements WithAssertions {
public class MaybeMonadTest implements WithAssertions {
private final int v = 1;
private final Function<Integer, Maybe<Integer>> f = i -> m(i * 2);
private final Function<Integer, Maybe<Integer>> g = i -> m(i + 6);
private final int v = 1;
private final Function<Integer, Maybe<Integer>> f = i -> m(i * 2);
private final Function<Integer, Maybe<Integer>> g = i -> m(i + 6);
private static Maybe<Integer> m(int value) {
return Maybe.maybe(value);
}
private static Maybe<Integer> m(int value) {
return Maybe.maybe(value);
}
@Test
public void leftIdentity() {
assertThat(
m(v).flatMap(f)
).isEqualTo(
f.apply(v)
);
}
@Test
public void leftIdentity() {
assertThat(
m(v).flatMap(f)
).isEqualTo(
f.apply(v)
);
}
@Test
public void rightIdentity() {
assertThat(
m(v).flatMap(x -> m(x))
).isEqualTo(
m(v)
);
}
@Test
public void rightIdentity() {
assertThat(
m(v).flatMap(x -> m(x))
).isEqualTo(
m(v)
);
}
@Test
public void associativity() {
assertThat(
m(v).flatMap(f).flatMap(g)
).isEqualTo(
m(v).flatMap(x -> f.apply(x).flatMap(g))
);
}
@Test
public void associativity() {
assertThat(
m(v).flatMap(f).flatMap(g)
).isEqualTo(
m(v).flatMap(x -> f.apply(x).flatMap(g))
);
}
}
#+END_SRC
}
#+END_SRC
**** Static Constructors
***** =static <T> Maybe<T> maybe(T value)=
*** Static Constructors
Create a Maybe for the value that may or may not be present.
**** =static <T> Maybe<T> maybe(T value)=
Where the value is =null=, that is taken as not being present.
Create a Maybe for the value that may or may not be present.
#+BEGIN_SRC java
final Maybe<Integer> just = Maybe.maybe(1);
final Maybe<Integer> nothing = Maybe.maybe(null);
#+END_SRC
Where the value is =null=, that is taken as not being present.
***** =static <T> Maybe<T> just(T value)=
#+BEGIN_SRC java
final Maybe<Integer> just = Maybe.maybe(1);
final Maybe<Integer> nothing = Maybe.maybe(null);
#+END_SRC
Create a Maybe for the value that is present.
The =value= must not be =null= or a =NullPointerException= will be thrown.
If you can't prove that the value won't be =null= you should use
=Maybe.maybe(value)= instead.
**** =static <T> Maybe<T> just(T value)=
#+BEGIN_SRC java
final Maybe<Integer> just = Maybe.just(1);
#+END_SRC
Create a Maybe for the value that is present.
***** =static <T> Maybe<T> nothing()=
The =value= must not be =null= or a =NullPointerException= will be thrown.
If you can't prove that the value won't be =null= you should use
=Maybe.maybe(value)= instead.
Create a Maybe for a lack of a value.
#+BEGIN_SRC java
final Maybe<Integer> just = Maybe.just(1);
#+END_SRC
#+BEGIN_SRC java
final Maybe<Integer> nothing = Maybe.nothing();
#+END_SRC
**** Instance Methods
**** =static <T> Maybe<T> nothing()=
***** =Maybe<T> filter(Predicate<T> predicate)=
Create a Maybe for a lack of a value.
Filter a Maybe by the predicate, replacing with Nothing when it fails.
#+BEGIN_SRC java
final Maybe<Integer> nothing = Maybe.nothing();
#+END_SRC
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue())
.filter(v -> v % 2 == 0);
#+END_SRC
***** =<R> Maybe<R> map(Function<T,R> f)=
*** Instance Methods
Applies the function to the value within the Maybe, returning the result within another Maybe.
**** =Maybe<T> filter(Predicate<T> predicate)=
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue())
.map(v -> v * 100);
#+END_SRC
Filter a Maybe by the predicate, replacing with Nothing when it fails.
***** =<R> Maybe<R> flatMap(Function<T,Maybe<R>> f)=
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue())
.filter(v -> v % 2 == 0);
#+END_SRC
Applies the function to the value within the =Maybe=, resulting in another =Maybe=, then flattens the resulting =Maybe<Maybe<T>>= into =Maybe<T>=.
Monad binder maps the Maybe into another Maybe using the binder method f
**** =<R> Maybe<R> map(Function<T,R> f)=
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue())
.flatMap(v -> Maybe.maybe(getValueFor(v)));
#+END_SRC
Applies the function to the value within the Maybe, returning the result within another Maybe.
***** =void match(Consumer<T> just, Runnable nothing)=
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue())
.map(v -> v * 100);
#+END_SRC
Matches the Maybe, either just or nothing, and performs either the Consumer, for Just, or Runnable for nothing.
#+BEGIN_SRC java
Maybe.maybe(getValue())
.match(
just -> workWithValue(just),
() -> nothingToWorkWith()
);
#+END_SRC
**** =<R> Maybe<R> flatMap(Function<T,Maybe<R>> f)=
***** =T orElse(T otherValue)=
Applies the function to the value within the =Maybe=, resulting in another =Maybe=, then flattens the resulting =Maybe<Maybe<T>>= into =Maybe<T>=.
A value to use when Maybe is Nothing.
Monad binder maps the Maybe into another Maybe using the binder method f
#+BEGIN_SRC java
final Integer value = Maybe.maybe(getValue())
.orElse(1);
#+END_SRC
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue())
.flatMap(v -> Maybe.maybe(getValueFor(v)));
#+END_SRC
***** =T orElseGet(Supplier<T> otherValueSupplier)=
Provide a value to use when Maybe is Nothing.
**** =void match(Consumer<T> just, Runnable nothing)=
#+BEGIN_SRC java
final Integer value = Maybe.maybe(getValue())
.orElseGet(() -> getDefaultValue());
#+END_SRC
Matches the Maybe, either just or nothing, and performs either the Consumer, for Just, or Runnable for nothing.
***** =void orElseThrow(Supplier<Exception> error)=
#+BEGIN_SRC java
Maybe.maybe(getValue())
.match(
just -> workWithValue(just),
() -> nothingToWorkWith()
);
#+END_SRC
Throw the exception if the Maybe is a Nothing.
#+BEGIN_SRC java
final Integer value = Maybe.maybe(getValue())
.orElseThrow(() -> new RuntimeException("error"));
#+END_SRC
**** =T orElse(T otherValue)=
***** =Maybe<T> peek(Consumer<T> consumer)=
A value to use when Maybe is Nothing.
Provide the value within the Maybe, if it exists, to the Consumer, and returns this Maybe. Conceptually equivalent to the idea of =ifPresent(...)=.
#+BEGIN_SRC java
final Integer value = Maybe.maybe(getValue())
.orElse(1);
#+END_SRC
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue())
.peek(v -> v.foo());
#+END_SRC
***** =void ifNothing(Runnable runnable)=
**** =T orElseGet(Supplier<T> otherValueSupplier)=
Run the runnable if the Maybe is a Nothing, otherwise do nothing.
Provide a value to use when Maybe is Nothing.
#+BEGIN_SRC java
Maybe.maybe(getValue())
.ifNothing(() -> doSomething());
#+END_SRC
#+BEGIN_SRC java
final Integer value = Maybe.maybe(getValue())
.orElseGet(() -> getDefaultValue());
#+END_SRC
***** =Stream<T> stream()=
Converts the Maybe into either a single value stream or an empty stream.
**** =void orElseThrow(Supplier<Exception> error)=
#+BEGIN_SRC java
final Stream<Integer> stream = Maybe.maybe(getValue())
.stream();
#+END_SRC
Throw the exception if the Maybe is a Nothing.
***** =boolean isJust()=
#+BEGIN_SRC java
final Integer value = Maybe.maybe(getValue())
.orElseThrow(() -> new RuntimeException("error"));
#+END_SRC
Checks if the Maybe is a Just.
#+BEGIN_SRC java
final boolean isJust = Maybe.maybe(getValue())
.isJust();
#+END_SRC
**** =Maybe<T> peek(Consumer<T> consumer)=
***** =boolean isNothing()=
Provide the value within the Maybe, if it exists, to the Consumer, and returns this Maybe. Conceptually equivalent to the idea of =ifPresent(...)=.
Checks if the Maybe is Nothing.
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue())
.peek(v -> v.foo());
#+END_SRC
#+BEGIN_SRC java
final boolean isNothing = Maybe.maybe(getValue())
.isNothing();
#+END_SRC
***** =Optional<T> toOptional()=
**** =void ifNothing(Runnable runnable)=
Convert the Maybe to an Optional.
Run the runnable if the Maybe is a Nothing, otherwise do nothing.
#+BEGIN_SRC java
Maybe.maybe(getValue())
.ifNothing(() -> doSomething());
#+END_SRC
**** =Stream<T> stream()=
Converts the Maybe into either a single value stream or an empty stream.
#+BEGIN_SRC java
final Stream<Integer> stream = Maybe.maybe(getValue())
.stream();
#+END_SRC
**** =boolean isJust()=
Checks if the Maybe is a Just.
#+BEGIN_SRC java
final boolean isJust = Maybe.maybe(getValue())
.isJust();
#+END_SRC
**** =boolean isNothing()=
Checks if the Maybe is Nothing.
#+BEGIN_SRC java
final boolean isNothing = Maybe.maybe(getValue())
.isNothing();
#+END_SRC
**** =Optional<T> toOptional()=
Convert the Maybe to an Optional.
#+BEGIN_SRC java
final Optional<Integer> optional = Maybe.maybe(getValue())
.toOptional();
#+END_SRC
#+BEGIN_SRC java
final Optional<Integer> optional = Maybe.maybe(getValue())
.toOptional();
#+END_SRC
** Result
:PROPERTIES:
:CUSTOM_ID: result
:END:
Allows handling error conditions without the need to catch exceptions.
@ -443,257 +447,278 @@
Result would have ignored the =flatMap= and skipped to the =match()= when it
would have called the error =Consumer=.
**** =Result= is a Monad
*** =Result= is a Monad
#+BEGIN_SRC java
package net.kemitix.mon;
import net.kemitix.mon.result.Result;
import org.assertj.core.api.WithAssertions;
import org.junit.Test;
import java.util.function.Function;
public class ResultMonadTest implements WithAssertions {
private final int v = 1;
private final Function<Integer, Result<Integer>> f = i -> r(i * 2);
private final Function<Integer, Result<Integer>> g = i -> r(i + 6);
private static Result<Integer> r(int v) {
return Result.ok(v);
}
@Test
public void leftIdentity() {
assertThat(
r(v).flatMap(f)
).isEqualTo(
f.apply(v)
);
}
@Test
public void rightIdentity() {
assertThat(
r(v).flatMap(x -> r(x))
).isEqualTo(
r(v)
);
}
@Test
public void associativity() {
assertThat(
r(v).flatMap(f).flatMap(g)
).isEqualTo(
r(v).flatMap(x -> f.apply(x).flatMap(g))
);
}
}
#+END_SRC
*** Static Constructors
**** =static <T> Result<T> of(Callable<T> callable)=
Create a Result for a output of the Callable.
If the Callable throws and Exception, then the Result will be an error and
will contain that exception.
This will be the main starting point for most Results where the callable
could throw an =Exception=.
#+BEGIN_SRC java
package net.kemitix.mon;
import net.kemitix.mon.result.Result;
import org.assertj.core.api.WithAssertions;
import org.junit.Test;
import java.util.function.Function;
public class ResultMonadTest implements WithAssertions {
private final int v = 1;
private final Function<Integer, Result<Integer>> f = i -> r(i * 2);
private final Function<Integer, Result<Integer>> g = i -> r(i + 6);
private static Result<Integer> r(int v) {
return Result.ok(v);
}
@Test
public void leftIdentity() {
assertThat(
r(v).flatMap(f)
).isEqualTo(
f.apply(v)
);
}
@Test
public void rightIdentity() {
assertThat(
r(v).flatMap(x -> r(x))
).isEqualTo(
r(v)
);
}
@Test
public void associativity() {
assertThat(
r(v).flatMap(f).flatMap(g)
).isEqualTo(
r(v).flatMap(x -> f.apply(x).flatMap(g))
);
}
}
final Result<Integer> okay = Result.of(() -> 1);
final Result<Integer> error = Result.of(() -> {throw new RuntimeException();});
#+END_SRC
**** Static Constructors
***** =static <T> Result<T> of(Callable<T> callable)=
**** =static <T> Result<T> ok(T value)=
Create a Result for a output of the Callable.
Create a Result for a success.
If the Callable throws and Exception, then the Result will be an error and
will contain that exception.
Use this where you have a value that you want to place into the Result context.
This will be the main starting point for most Results where the callable
could throw an =Exception=.
#+BEGIN_SRC java
final Result<Integer> okay = Result.ok(1);
#+END_SRC
#+BEGIN_SRC java
final Result<Integer> okay = Result.of(() -> 1);
final Result<Integer> error = Result.of(() -> {throw new RuntimeException();});
#+END_SRC
***** =static <T> Result<T> ok(T value)=
**** =static <T> Result<T> error(Throwable error)=
Create a Result for a success.
Create a Result for an error.
Use this where you have a value that you want to place into the Result context.
#+BEGIN_SRC java
final Result<Integer> error = Result.error(new RuntimeException());
#+END_SRC
#+BEGIN_SRC java
final Result<Integer> okay = Result.ok(1);
#+END_SRC
***** =static <T> Result<T> error(Throwable error)=
*** Static Methods
Create a Result for an error.
These static methods provide integration with the =Maybe= class.
#+BEGIN_SRC java
final Result<Integer> error = Result.error(new RuntimeException());
#+END_SRC
#+BEGIN_SRC java
#+END_SRC
**** Static Methods
**** =static <T> Maybe<T> toMaybe(Result<T> result)=
These static methods provide integration with the =Maybe= class.
Creates a =Maybe= from the =Result=, where the =Result= is a success, then
the =Maybe= will contain the value. However, if the =Result= is an error
then the =Maybe= will be nothing.
#+BEGIN_SRC java
#+END_SRC
#+BEGIN_SRC java
final Result<Integer> result = Result.of(() -> getValue());
final Maybe<Integer> maybe = Result.toMaybe(result);
#+END_SRC
***** =static <T> Maybe<T> toMaybe(Result<T> result)=
Creates a =Maybe= from the =Result=, where the =Result= is a success, then
the =Maybe= will contain the value. However, if the =Result= is an error
then the =Maybe= will be nothing.
**** =static <T> Result<T> fromMaybe(Maybe<T> maybe, Supplier<Throwable> error)=
#+BEGIN_SRC java
final Result<Integer> result = Result.of(() -> getValue());
final Maybe<Integer> maybe = Result.toMaybe(result);
#+END_SRC
Creates a =Result= from the =Maybe=, where the =Result= will be an error
if the =Maybe= is nothing. Where the =Maybe= is nothing, then the
=Supplier<Throwable>= will provide the error for the =Result=.
***** =static <T> Result<T> fromMaybe(Maybe<T> maybe, Supplier<Throwable> error)=
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue());
final Result<Integer> result = Result.fromMaybe(maybe, () -> new NoSuchFileException("filename"));
#+END_SRC
Creates a =Result= from the =Maybe=, where the =Result= will be an error
if the =Maybe= is nothing. Where the =Maybe= is nothing, then the
=Supplier<Throwable>= will provide the error for the =Result=.
#+BEGIN_SRC java
final Maybe<Integer> maybe = Maybe.maybe(getValue());
final Result<Integer> result = Result.fromMaybe(maybe, () -> new NoSuchFileException("filename"));
#+END_SRC
**** =static <T> Result<Maybe<T>> invert(Maybe<Result<T>> maybeResult)=
***** =static <T> Result<Maybe<T>> invert(Maybe<Result<T>> maybeResult)=
Swaps the =Result= within a =Maybe=, so that =Result= contains a =Maybe=.
Swaps the =Result= within a =Maybe=, so that =Result= contains a =Maybe=.
#+BEGIN_SRC java
final Maybe<Result<Integer>> maybe = Maybe.maybe(Result.of(() -> getValue()));
final Result<Maybe<Integer>> result = Result.invert(maybe);
#+END_SRC
#+BEGIN_SRC java
final Maybe<Result<Integer>> maybe = Maybe.maybe(Result.of(() -> getValue()));
final Result<Maybe<Integer>> result = Result.invert(maybe);
#+END_SRC
***** =static <T,R> Result<Maybe<R>> flatMapMaybe(Result<Maybe<T>> maybeResult, Function<Maybe<T>,Result<Maybe<R>>> f)=
**** =static <T,R> Result<Maybe<R>> flatMapMaybe(Result<Maybe<T>> maybeResult, Function<Maybe<T>,Result<Maybe<R>>> f)=
Applies the function to the contents of a Maybe within the Result.
Applies the function to the contents of a Maybe within the Result.
#+BEGIN_SRC java
final Result<Maybe<Integer>> result = Result.of(() -> Maybe.maybe(getValue()));
final Result<Maybe<Integer>> maybeResult = Result.flatMapMaybe(result, maybe -> Result.of(() -> maybe.map(v -> v * 2)));
#+END_SRC
#+BEGIN_SRC java
final Result<Maybe<Integer>> result = Result.of(() -> Maybe.maybe(getValue()));
final Result<Maybe<Integer>> maybeResult = Result.flatMapMaybe(result, maybe -> Result.of(() -> maybe.map(v -> v * 2)));
#+END_SRC
**** Instance Methods
***** <R> Result<R> map(Function<T,R> f)
*** Instance Methods
Applies the function to the value within the Functor, returning the result
within a Functor.
**** =<R> Result<R> map(Function<T,R> f)=
#+BEGIN_SRC java
final Result<String> result = Result.of(() -> getValue())
.map(v -> String.valueOf(v));
#+END_SRC
Applies the function to the value within the Functor, returning the result
within a Functor.
***** <R> Result<R> flatMap(Function<T,Result<R>> f)
#+BEGIN_SRC java
final Result<String> result = Result.of(() -> getValue())
.map(v -> String.valueOf(v));
#+END_SRC
Returns a new Result consisting of the result of applying the function to
the contents of the Result.
#+BEGIN_SRC java
final Result<String> result = Result.of(() -> getValue())
.flatMap(v -> Result.of(() -> String.valueOf(v)));
#+END_SRC
**** =<R> Result<R> flatMap(Function<T,Result<R>> f)=
***** <R> Result<R> andThen(Function<T,Callable<R>> f)
Returns a new Result consisting of the result of applying the function to
the contents of the Result.
Maps a Success Result to another Result using a Callable that is able to
throw a checked exception.
#+BEGIN_SRC java
final Result<String> result = Result.of(() -> getValue())
.flatMap(v -> Result.of(() -> String.valueOf(v)));
#+END_SRC
#+BEGIN_SRC java
final Result<String> result = Result.of(() -> getValue())
.andThen(v -> () -> {throw new IOException();});
#+END_SRC
***** void match(Consumer<T> onSuccess, Consumer<Throwable> onError)
**** =<R> Result<R> andThen(Function<T,Callable<R>> f)=
Matches the Result, either success or error, and supplies the appropriate
Consumer with the value or error.
Maps a Success Result to another Result using a Callable that is able to
throw a checked exception.
#+BEGIN_SRC java
Result.of(() -> getValue())
.match(
success -> System.out.println(success),
error -> System.err.println("error")
);
#+END_SRC
#+BEGIN_SRC java
final Result<String> result = Result.of(() -> getValue())
.andThen(v -> () -> {throw new IOException();});
#+END_SRC
***** Result<T> recover(Function<Throwable,Result<T>> f)
Provide a way to attempt to recover from an error state.
**** =void match(Consumer<T> onSuccess, Consumer<Throwable> onError)=
#+BEGIN_SRC java
Matches the Result, either success or error, and supplies the appropriate
Consumer with the value or error.
#+BEGIN_SRC java
Result.of(() -> getValue())
.match(
success -> System.out.println(success),
error -> System.err.println("error")
);
#+END_SRC
**** =Result<T> recover(Function<Throwable,Result<T>> f)=
Provide a way to attempt to recover from an error state.
#+BEGIN_SRC java
final Result<Integer> result = Result.of(() -> getValue())
.recover(e -> Result.of(() -> getSafeValue(e)));
#+END_SRC
**** =Result<T> peek(Consumer<T> consumer)=
Provide the value within the Result, if it is a success, to the Consumer,
and returns this Result.
#+BEGIN_SRC java
final Result<Integer> result = Result.of(() -> getValue())
.peek(v -> System.out.println(v));
#+END_SRC
**** =Result<T> thenWith(Function<T,WithResultContinuation<T>> f)=
Perform the continuation with the current Result value then return the
current Result, assuming there was no error in the continuation.
#+BEGIN_SRC java
final Result<Integer> result = Result.of(() -> getValue())
.recover(e -> Result.of(() -> getSafeValue(e)));
#+END_SRC
.thenWith(v -> () -> System.out.println(v))
.thenWith(v -> () -> {throw new IOException();});
#+END_SRC
***** Result<T> peek(Consumer<T> consumer)
Provide the value within the Result, if it is a success, to the Consumer,
and returns this Result.
**** =Result<Maybe<T>> maybe(Predicate<T> predicate)=
#+BEGIN_SRC java
final Result<Integer> result = Result.of(() -> getValue())
.peek(v -> System.out.println(v));
#+END_SRC
Wraps the value within the Result in a Maybe, either a Just if the
predicate is true, or Nothing.
***** Result<T> thenWith(Function<T,WithResultContinuation<T>> f)
#+BEGIN_SRC java
final Result<Maybe<Integer>> result = Result.of(() -> getValue())
.maybe(v -> v % 2 == 0);
#+END_SRC
Perform the continuation with the current Result value then return the
current Result, assuming there was no error in the continuation.
#+BEGIN_SRC java
final Result<Integer> result = Result.of(() -> getValue())
.thenWith(v -> () -> System.out.println(v))
.thenWith(v -> () -> {throw new IOException();});
#+END_SRC
**** =T orElseThrow()=
***** Result<Maybe<T>> maybe(Predicate<T> predicate)
Extracts the successful value from the result, or throws the error
Throwable.
Wraps the value within the Result in a Maybe, either a Just if the
predicate is true, or Nothing.
#+BEGIN_SRC java
final Integer result = Result.of(() -> getValue())
.orElseThrow();
#+END_SRC
#+BEGIN_SRC java
final Result<Maybe<Integer>> result = Result.of(() -> getValue())
.maybe(v -> v % 2 == 0);
#+END_SRC
***** T orElseThrow()
**** =void onError(Consumer<Throwable> errorConsumer)=
Extracts the successful value from the result, or throws the error
Throwable.
A handler for error states.
#+BEGIN_SRC java
final Integer result = Result.of(() -> getValue())
.orElseThrow();
#+END_SRC
#+BEGIN_SRC java
Result.of(() -> getValue())
.onError(e -> handleError(e));
#+END_SRC
***** void onError(Consumer<Throwable> errorConsumer)
A handler for error states.
**** =boolean isOkay()=
#+BEGIN_SRC java
Result.of(() -> getValue())
.onError(e -> handleError(e));
#+END_SRC
Checks if the Result is a success.
***** boolean isOkay()
#+BEGIN_SRC java
final boolean isOkay = Result.of(() -> getValue())
.isOkay();
#+END_SRC
Checks if the Result is a success.
#+BEGIN_SRC java
final boolean isOkay = Result.of(() -> getValue())
.isOkay();
#+END_SRC
**** =boolean isError()=
***** boolean isError()
Checks if the Result is an error.
#+BEGIN_SRC java
final boolean isError = Result.of(() -> getValue())
.isError();
#+END_SRC
Checks if the Result is an error.
#+BEGIN_SRC java
final boolean isError = Result.of(() -> getValue())
.isError();
#+END_SRC