fromPredicate<A, B> function

TaskEither<A, B> Function(B value) fromPredicate<A, B>(Predicate<B> predicate, A leftValue())

Creates a TaskEither based on a predicate function.

This function evaluates a given predicate using the provided value. If the predicate evaluates to true, the result is a TaskEither that resolves to a e.Right with the same value. If the predicate evaluates to false, the result is a TaskEither that resolves to a e.Left with the value produced by the leftValue function.

/// Example:
final predicate = (int value) => value > 5;
final leftValue = () => "Less than or equal to 5";
final taskEitherFunction = fromPredicate<String, int>(predicate, leftValue);

taskEitherFunction(6).value().then((result) {
  if (result is e.Right) {
    print(result.value); // Outputs: 6
  } else if (result is e.Left) {
    print(result.value); // This line won't execute for the value 6
  }
});

taskEitherFunction(4).value().then((result) {
  if (result is e.Right) {
    print(result.value); // This line won't execute for the value 4
  } else if (result is e.Left) {
    print(result.value); // Outputs: "Less than or equal to 5"
  }
});

A: The type of the left value. B: The type of the right value and the input value.

Returns a function that takes a value of type B and produces a TaskEither of A or B.

Implementation

TaskEither<A, B> Function(B value) fromPredicate<A, B>(
  Predicate<B> predicate,
  A Function() leftValue,
) {
  return (B value) =>
      predicate(value) ? right<A, B>(value) : left<A, B>(leftValue());
}