Add Either.liftPredicate

.changeset/two-bananas-mix.md

@@ -0,0 +1,5 @@
+---
+"effect": minor
+---
+
+Add Either.liftPredicate

packages/effect/dtslint/Either.ts

@@ -110,6 +110,80 @@ string$string.pipe(Either.andThen(string$number))
 // $ExpectType Either<number, string>
 string$string.pipe(Either.andThen(() => string$number))
 
+// -------------------------------------------------------------------------------------
+// liftPredicate
+// -------------------------------------------------------------------------------------
+
+declare const primitiveNumber: number
+declare const primitiveNumberOrString: string | number
+declare const predicateNumbersOrStrings: Predicate.Predicate<number | string>
+
+// $ExpectType Either<string, "b">
+pipe(
+  primitiveNumberOrString,
+  Either.liftPredicate(Predicate.isString, (
+    _s // $ExpectType string | number
+  ) => "b" as const)
+)
+
+// $ExpectType Either<string, "b">
+Either.liftPredicate(primitiveNumberOrString, Predicate.isString, (
+  _s // $ExpectType string | number
+) => "b" as const)
+
+// $ExpectType Either<number, "b">
+pipe(
+  primitiveNumberOrString,
+  Either.liftPredicate(
+    (
+      n // $ExpectType string | number
+    ): n is number => typeof n === "number",
+    (
+      _s // $ExpectType string | number
+    ) => "b" as const
+  )
+)
+
+// $ExpectType Either<number, "b">
+Either.liftPredicate(
+  primitiveNumberOrString,
+  (
+    n // $ExpectType string | number
+  ): n is number => typeof n === "number",
+  (
+    _s // $ExpectType string | number
+  ) => "b" as const
+)
+
+// $ExpectType Either<string | number, "b">
+pipe(
+  primitiveNumberOrString,
+  Either.liftPredicate(predicateNumbersOrStrings, (
+    _s // $ExpectType string | number
+  ) => "b" as const)
+)
+
+// $ExpectType Either<number, "b">
+pipe(
+  primitiveNumber,
+  Either.liftPredicate(predicateNumbersOrStrings, (
+    _s // $ExpectType number
+  ) => "b" as const)
+)
+
+// $ExpectType Either<number, "b">
+pipe(
+  primitiveNumber,
+  Either.liftPredicate(
+    (
+      _n // $ExpectType number
+    ) => true,
+    (
+      _s // $ExpectType number
+    ) => "b" as const
+  )
+)
+
 // -------------------------------------------------------------------------------------
 // filterOrLeft
 // -------------------------------------------------------------------------------------

packages/effect/src/Either.ts

@@ -390,6 +390,57 @@ export const match: {
   }): B | C => isLeft(self) ? onLeft(self.left) : onRight(self.right)
 )
 
+/**
+ * Transforms a `Predicate` function into a `Right` of the input value if the predicate returns `true`
+ * or `Left` of the result of the provided function if the predicate returns false
+ *
+ * @param predicate - A `Predicate` function that takes in a value of type `A` and returns a boolean.
+ *
+ * @example
+ * import { pipe, Either } from "effect"
+ *
+ * const isPositive = (n: number): boolean => n > 0
+ *
+ * assert.deepStrictEqual(
+ *   pipe(
+ *     1,
+ *     Either.liftPredicate(isPositive, n => `${n} is not positive`)
+ *   ),
+ *   Either.right(1)
+ * )
+ * assert.deepStrictEqual(
+ *   pipe(
+ *     0,
+ *     Either.liftPredicate(isPositive, n => `${n} is not positive`)
+ *   ),
+ *   Either.left("0 is not positive")
+ * )
+ *
+ * @category lifting
+ * @since 3.4.0
+ */
+export const liftPredicate: {
+  <A, B extends A, E>(refinement: Refinement<NoInfer<A>, B>, orLeftWith: (a: NoInfer<A>) => E): (a: A) => Either<B, E>
+  <A, E>(
+    predicate: Predicate<NoInfer<A>>,
+    orLeftWith: (a: NoInfer<A>) => E
+  ): (a: A) => Either<A, E>
+  <A, E, B extends A>(
+    self: A,
+    refinement: Refinement<A, B>,
+    orLeftWith: (a: A) => E
+  ): Either<B, E>
+  <A, E>(
+    self: A,
+    predicate: Predicate<NoInfer<A>>,
+    orLeftWith: (a: NoInfer<A>) => E
+  ): Either<A, E>
+} = dual(
+  3,
+  <A, E>(a: A, predicate: Predicate<A>, orLeftWith: (a: A) => E): Either<A, E> =>
+    predicate(a) ? right(a) : left(orLeftWith(a))
+)
+
 /**
  * Filter the right value with the provided function.
  * If the predicate fails, set the left value with the result of the provided function.

packages/effect/test/Either.test.ts

@@ -169,6 +169,47 @@ describe("Either", () => {
     Util.deepStrictEqual(Either.flip(Either.left("b")), Either.right("b"))
   })
 
+  it("liftPredicate", () => {
+    const isPositivePredicate = (n: number) => n > 0
+    const onPositivePredicateError = (n: number) => `${n} is not positive`
+    const isNumberRefinement = (n: string | number): n is number => typeof n === "number"
+    const onNumberRefinementError = (n: string | number) => `${n} is not a number`
+
+    Util.deepStrictEqual(
+      pipe(1, Either.liftPredicate(isPositivePredicate, onPositivePredicateError)),
+      Either.right(1)
+    )
+    Util.deepStrictEqual(
+      pipe(-1, Either.liftPredicate(isPositivePredicate, onPositivePredicateError)),
+      Either.left(`-1 is not positive`)
+    )
+    Util.deepStrictEqual(
+      pipe(1, Either.liftPredicate(isNumberRefinement, onNumberRefinementError)),
+      Either.right(1)
+    )
+    Util.deepStrictEqual(
+      pipe("string", Either.liftPredicate(isNumberRefinement, onNumberRefinementError)),
+      Either.left(`string is not a number`)
+    )
+
+    Util.deepStrictEqual(
+      Either.liftPredicate(1, isPositivePredicate, onPositivePredicateError),
+      Either.right(1)
+    )
+    Util.deepStrictEqual(
+      Either.liftPredicate(-1, isPositivePredicate, onPositivePredicateError),
+      Either.left(`-1 is not positive`)
+    )
+    Util.deepStrictEqual(
+      Either.liftPredicate(1, isNumberRefinement, onNumberRefinementError),
+      Either.right(1)
+    )
+    Util.deepStrictEqual(
+      Either.liftPredicate("string", isNumberRefinement, onNumberRefinementError),
+      Either.left(`string is not a number`)
+    )
+  })
+
   it("filterOrLeft", () => {
     Util.deepStrictEqual(Either.filterOrLeft(Either.right(1), (n) => n > 0, () => "a"), Either.right(1))
     Util.deepStrictEqual(Either.filterOrLeft(Either.right(1), (n) => n > 1, () => "a"), Either.left("a"))