feat: slice.Exists, slice.Forall

README.md

@@ -438,6 +438,8 @@ Some utilities that are convenient when working with slices.
 - `slice.FoldLeft[A any, B any](as []A, zero B, f func(B, A)B) (res B)`
 - `slice.Filter[A any](as []A, p func(a A) bool) (res []A)`
 - `slice.FilterNot[A any](as []A, p func(a A) bool) (res []A)` - same as `Filter`, but inverses the predicate `p`.
+- `slice.Exists[A any](p Predicate[A]) Predicate[[]A]` - Exists returns a predicate on slices. The predicate is true if there is an element that satisfy the given element-wise predicate. It's false for an empty slice.
+- `slice.Forall[A any](p Predicate[A]) Predicate[[]A]` - Forall returns a predicate on slices. The predicate is true if all elements satisfy the given element-wise predicate. It's true for an empty slice.
 - `slice.Collect[A any, B any](as []A, f func(a A) option.Option[B]) (bs []B)` - Collect runs through the slice, executes the given function and only keeps good returned values.
 - `slice.Count[A any](as []A, predicate Predicate[A]) (cnt int)` - Count counts the number of elements that satisfy the given predicate.
 - `slice.Flatten[A any](ass [][]A)(aas[]A)`

slice/slice.go

@@ -181,3 +181,35 @@ func Collect[A any, B any](as []A, f func(a A) option.Option[B]) (bs []B) {
 	}
 	return
 }
+
+// Exists returns a predicate on slices.
+// The predicate is true if there is an element that satisfy the given element-wise predicate.
+// It's false for an empty slice.
+func Exists[A any](p Predicate[A]) Predicate[[]A] {
+	return func(as []A) (res bool) {
+		res = false
+		for _, a := range as {
+			if p(a) {
+				res = true
+				break
+			}
+		}
+		return
+	}
+}
+
+// Forall returns a predicate on slices.
+// The predicate is true if all elements satisfy the given element-wise predicate.
+// It's true for an empty slice.
+func Forall[A any](p Predicate[A]) Predicate[[]A] {
+	return func(as []A) (res bool) {
+		res = true
+		for _, a := range as {
+			if !p(a) {
+				res = false
+				break
+			}
+		}
+		return
+	}
+}

slice/slice_test.go

@@ -12,14 +12,26 @@ func IsEven(i int) bool {
 	return i%2 == 0
 }
 
+func IsPositive(i int) bool {
+	return i > 0
+}
+func IsNegative(i int) bool {
+	return i < 0
+}
+
 var nats10Values = []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
 
 func TestFilter(t *testing.T) {
 	sumEven := slice.Sum(slice.Filter(nats10Values, IsEven))
 	assert.Equal(t, 30, sumEven)
 
 	sumOdd := slice.Sum(slice.FilterNot(nats10Values, IsEven))
+
 	assert.Equal(t, 25, sumOdd)
+	assert.True(t, slice.Exists(IsEven)(nats10Values))
+	assert.False(t, slice.Forall(IsEven)(nats10Values))
+	assert.True(t, slice.Forall(IsPositive)(nats10Values))
+	assert.False(t, slice.Forall(IsNegative)(nats10Values))
 }
 
 func TestFlatten(t *testing.T) {