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Add traverse, zip and orEmpty to Option #53

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Add traverse, zip and orEmpty to Option #53

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3 changes: 3 additions & 0 deletions lib/api/lib.api
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Original file line number Diff line number Diff line change
Expand Up @@ -236,8 +236,11 @@ public final class app/cash/quiver/extensions/OptionKt {
public static final fun forEach (Larrow/core/Option;Lkotlin/jvm/functions/Function1;)V
public static final fun ifAbsent (Larrow/core/Option;Lkotlin/jvm/functions/Function0;)V
public static final fun or (Larrow/core/Option;Larrow/core/Option;)Larrow/core/Option;
public static final fun orEmpty (Larrow/core/Option;Lkotlin/jvm/functions/Function1;)Ljava/lang/String;
public static final fun toValidatedNel (Larrow/core/Option;Lkotlin/jvm/functions/Function0;)Larrow/core/Validated;
public static final fun traverseOp (Larrow/core/Option;Lkotlin/jvm/functions/Function1;)Larrow/core/Either;
public static final fun unit (Larrow/core/Option;)Larrow/core/Option;
public static final fun zipOp (Larrow/core/Option;Larrow/core/Option;Lkotlin/jvm/functions/Function2;)Larrow/core/Option;
}

public final class app/cash/quiver/extensions/ResultKt {
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26 changes: 26 additions & 0 deletions lib/src/main/kotlin/app/cash/quiver/extensions/Option.kt
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Expand Up @@ -2,11 +2,15 @@

package app.cash.quiver.extensions

import arrow.core.Either
import arrow.core.None
import arrow.core.Option
import arrow.core.Some
import arrow.core.ValidatedNel
import arrow.core.getOrElse
import arrow.core.nonEmptyListOf
import arrow.core.raise.option
import arrow.core.right

/**
* Takes a function to run if your Option is None. Returns Unit if your Option is Some.
Expand Down Expand Up @@ -41,3 +45,25 @@ infix fun <T> Option<T>.or(other: Option<T>): Option<T> = when (this) {
is Some -> this
is None -> other
}

/**
* Given a function that returns an Either, will turn your Option of A into an Option of B in the context of Either,
* where the Left value will always be the None.
*/
inline fun <E, A, B> Option<A>.traverseOp(fa: (A) -> Either<E, B>): Either<E, Option<B>> = fold(
{ None.right() },
{ fa(it).map(::Some) }
)
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It's unfortunate we have to use traverseOp and zipOp, that really reduces the value of back-porting these.

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@aparkersquare aparkersquare Sep 7, 2023 •
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traverseEither and zipOption would be more consistent with the variants on NonEmptyList (which have recently been back-ported to quiver).

We could then add traverse and zip when arrow finally removes them?

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I feel like using straight traverse and zip is worth the wait. Let's lean on Arrow to fully remove them.

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Agreed. I'll open a new PR with just orEmpty then if you're happy with it


/**
* Given an optional value A and B, will return you an optional C
*/
inline fun <A, B, C> Option<A>.zipOp(b: Option<B>, f: (A, B) -> C): Option<C> = option {
f(bind(), b.bind())
}

/**
* Will return an empty string if the Option supplied is None
*/
fun <T> Option<T>.orEmpty(f: (T) -> String): String = this.map(f).getOrElse { "" }

23 changes: 23 additions & 0 deletions lib/src/test/kotlin/app/cash/quiver/extensions/OptionTest.kt
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Original file line number Diff line number Diff line change
@@ -1,7 +1,10 @@
package app.cash.quiver.extensions

import arrow.core.None
import arrow.core.right
import arrow.core.some
import io.kotest.assertions.arrow.core.shouldBeRight
import io.kotest.assertions.arrow.core.shouldBeSome
import io.kotest.core.spec.style.StringSpec
import io.kotest.matchers.shouldBe
import io.kotest.property.Arb
Expand Down Expand Up @@ -29,4 +32,24 @@ class OptionTest : StringSpec({
None.or(other) shouldBe other
}
}

"traverse returns an either of option" {
"apple".some().traverseOp {
it.length.right()
} shouldBeRight (5.some())
}

"zip returns an optional combination of optional values" {
5.some().zipOp("apple".some()) { a: Int, b: String ->
b.length * a
} shouldBeSome 25
}
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Suggested change
}
}

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@aparkersquare aparkersquare Sep 7, 2023 •
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I think the indent on line 46 is actually correct (2).

But the following two tests have incorrect indent (4).


"orEmpty returns an empty string if used on a None" {
None.orEmpty { "I am an useless string " } shouldBe ""
}

"orEmpty returns the string supplied if value is Some" {
"apple".some().orEmpty { "I wanna eat $it" } shouldBe "I wanna eat apple"
}
})
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