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Commitcc0cda9

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MaybeT implements MonadError
1 parentd3a049c commitcc0cda9

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3 files changed

+36
-2
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3 files changed

+36
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‎CHANGELOG.md

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@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/).
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###Changed
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-`IterateT#unfold` now only computes a single`Pure` for the given input
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-`ReaderT#fmap` and`StateT#fmap` avoid unnecessary calls to`pure`
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-`MaybeT` implements`MonadError`
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###Added
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-`$`, function application represented as a higher-order`Fn2`

‎src/main/java/com/jnape/palatable/lambda/monad/transformer/builtin/MaybeT.java

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@@ -1,6 +1,7 @@
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packagecom.jnape.palatable.lambda.monad.transformer.builtin;
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importcom.jnape.palatable.lambda.adt.Maybe;
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importcom.jnape.palatable.lambda.adt.Unit;
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importcom.jnape.palatable.lambda.functions.Fn1;
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importcom.jnape.palatable.lambda.functions.recursion.RecursiveResult;
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importcom.jnape.palatable.lambda.functions.specialized.Lift;
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importcom.jnape.palatable.lambda.functor.builtin.Compose;
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importcom.jnape.palatable.lambda.functor.builtin.Lazy;
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importcom.jnape.palatable.lambda.monad.Monad;
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importcom.jnape.palatable.lambda.monad.MonadError;
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importcom.jnape.palatable.lambda.monad.MonadRec;
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importcom.jnape.palatable.lambda.monad.transformer.MonadT;
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importjava.util.Objects;
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importstaticcom.jnape.palatable.lambda.adt.Maybe.just;
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importstaticcom.jnape.palatable.lambda.adt.Maybe.nothing;
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importstaticcom.jnape.palatable.lambda.adt.Unit.UNIT;
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importstaticcom.jnape.palatable.lambda.functions.Fn0.fn0;
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importstaticcom.jnape.palatable.lambda.functions.builtin.fn1.Constantly.constantly;
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importstaticcom.jnape.palatable.lambda.functions.recursion.RecursiveResult.terminate;
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@@ -26,7 +30,7 @@
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* @param <A> the carrier type
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*/
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publicfinalclassMaybeT<MextendsMonadRec<?,M>,A>implements
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MonadT<M,A,MaybeT<M, ?>,MaybeT<?, ?>> {
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MonadT<M,A,MaybeT<M, ?>,MaybeT<?, ?>>,MonadError<Unit,A,MaybeT<M, ?>> {
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privatefinalMonadRec<Maybe<A>,M>mma;
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@@ -67,6 +71,24 @@ public MaybeT<M, A> or(MaybeT<M, A> other) {
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a ->mMaybeA.pure(just(a)))));
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}
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/**
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* {@inheritDoc}
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*/
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@Override
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publicMaybeT<M,A>throwError(Unitunit) {
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returnmaybeT(mma.pure(nothing()));
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}
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/**
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* {@inheritDoc}
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*/
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@Override
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publicMaybeT<M,A>catchError(Fn1<?superUnit, ?extendsMonad<A,MaybeT<M, ?>>>recoveryFn) {
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returnmaybeT(mma.flatMap(maybeA ->maybeA.match(
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fn0(() ->recoveryFn.apply(UNIT).<MaybeT<M,A>>coerce().runMaybeT()),
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a ->mma.pure(just(a)))));
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}
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/**
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* {@inheritDoc}
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*/

‎src/test/java/com/jnape/palatable/lambda/monad/transformer/builtin/MaybeTTest.java

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@@ -22,14 +22,18 @@
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importstaticcom.jnape.palatable.lambda.adt.Either.right;
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importstaticcom.jnape.palatable.lambda.adt.Maybe.just;
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importstaticcom.jnape.palatable.lambda.adt.Maybe.nothing;
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importstaticcom.jnape.palatable.lambda.adt.Unit.UNIT;
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importstaticcom.jnape.palatable.lambda.functions.builtin.fn2.GT.gt;
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importstaticcom.jnape.palatable.lambda.functions.builtin.fn2.LT.lt;
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importstaticcom.jnape.palatable.lambda.functor.builtin.Identity.pureIdentity;
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importstaticcom.jnape.palatable.lambda.functor.builtin.Lazy.lazy;
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importstaticcom.jnape.palatable.lambda.io.IO.io;
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importstaticcom.jnape.palatable.lambda.monad.transformer.builtin.MaybeT.*;
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importstaticcom.jnape.palatable.lambda.monad.transformer.builtin.MaybeT.liftMaybeT;
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importstaticcom.jnape.palatable.lambda.monad.transformer.builtin.MaybeT.maybeT;
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importstaticcom.jnape.palatable.lambda.monad.transformer.builtin.MaybeT.pureMaybeT;
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importstaticcom.jnape.palatable.traitor.framework.Subjects.subjects;
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importstaticorg.junit.Assert.assertEquals;
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importstatictestsupport.assertion.MonadErrorAssert.assertLaws;
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@RunWith(Traits.class)
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publicclassMaybeTTest {
@@ -41,6 +45,13 @@ public class MaybeTTest {
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maybeT(left("foo")));
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}
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@Test
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publicvoidmonadError() {
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assertLaws(subjects(maybeT(newIdentity<>(nothing())),maybeT(newIdentity<>(just(1)))),
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UNIT,
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e ->maybeT(newIdentity<>(just(2))));
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}
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@Test
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publicvoidlazyZip() {
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assertEquals(maybeT(right(just(2))),

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