fn: add slice utilities

fn/go.mod

@@ -4,5 +4,12 @@ go 1.19
 
 require (
 	github.com/lightninglabs/neutrino/cache v1.1.2
+	github.com/stretchr/testify v1.8.1
 	golang.org/x/exp v0.0.0-20231226003508-02704c960a9b
 )
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

fn/go.sum

@@ -1,8 +1,21 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/lightninglabs/neutrino/cache v1.1.2 h1:C9DY/DAPaPxbFC+xNNEI/z1SJY9GS3shmlu5hIQ798g=
 github.com/lightninglabs/neutrino/cache v1.1.2/go.mod h1:XJNcgdOw1LQnanGjw8Vj44CvguYA25IMKjWFZczwZuo=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
 github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
+github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
 golang.org/x/exp v0.0.0-20231226003508-02704c960a9b h1:kLiC65FbiHWFAOu+lxwNPujcsl8VYyTYYEZnsOO1WK4=
 golang.org/x/exp v0.0.0-20231226003508-02704c960a9b/go.mod h1:iRJReGqOEeBhDZGkGbynYwcHlctCvnjTYIamk7uXpHI=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

fn/slice.go

@@ -0,0 +1,170 @@
+package fn
+
+// All returns true when the supplied predicate evaluates to true for all of
+// the values in the slice.
+func All[A any](pred func(A) bool, s []A) bool {
+	for _, val := range s {
+		if !pred(val) {
+			return false
+		}
+	}
+
+	return true
+}
+
+// Any returns true when the supplied predicate evaluates to true for any of
+// the values in the slice.
+func Any[A any](pred func(A) bool, s []A) bool {
+	for _, val := range s {
+		if pred(val) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// Map applies the function argument to all members of the slice and returns a
+// slice of those return values.
+func Map[A, B any](f func(A) B, s []A) []B {
+	res := make([]B, 0, len(s))
+
+	for _, val := range s {
+		res = append(res, f(val))
+	}
+
+	return res
+}
+
+// Filter creates a new slice of values where all the members of the returned
+// slice pass the predicate that is supplied in the argument.
+func Filter[A any](pred func(A) bool, s []A) []A {
+	res := make([]A, 0)
+
+	for _, val := range s {
+		if pred(val) {
+			res = append(res, val)
+		}
+	}
+
+	return res
+}
+
+// Foldl iterates through all members of the slice left to right and reduces
+// them pairwise with an accumulator value that is seeded with the seed value in
+// the argument.
+func Foldl[A, B any](f func(B, A) B, seed B, s []A) B {
+	acc := seed
+
+	for _, val := range s {
+		acc = f(acc, val)
+	}
+
+	return acc
+}
+
+// Foldr, is exactly like Foldl except that it iterates over the slice from
+// right to left.
+func Foldr[A, B any](f func(A, B) B, seed B, s []A) B {
+	acc := seed
+
+	for i := range s {
+		acc = f(s[len(s)-1-i], acc)
+	}
+
+	return acc
+}
+
+// Find returns the first value that passes the supplied predicate, or None if
+// the value wasn't found.
+func Find[A any](pred func(A) bool, s []A) Option[A] {
+	for _, val := range s {
+		if pred(val) {
+			return Some(val)
+		}
+	}
+
+	return None[A]()
+}
+
+// Flatten takes a slice of slices and returns a concatenation of those slices.
+func Flatten[A any](s [][]A) []A {
+	sz := Foldr(
+		func(l []A, acc uint64) uint64 {
+			return uint64(len(l)) + acc
+		}, 0, s,
+	)
+
+	res := make([]A, 0, sz)
+
+	for _, val := range s {
+		res = append(res, val...)
+	}
+
+	return res
+}
+
+// Replicate generates a slice of values initialized by the prototype value.
+func Replicate[A any](n uint, val A) []A {
+	res := make([]A, n)
+
+	for i := range res {
+		res[i] = val
+	}
+
+	return res
+}
+
+// Span, applied to a predicate and a slice, returns two slices where the first
+// element is the longest prefix (possibly empty) of slice elements that
+// satisfy the predicate and second element is the remainder of the slice.
+func Span[A any](pred func(A) bool, s []A) ([]A, []A) {
+	for i := range s {
+		if !pred(s[i]) {
+			fst := make([]A, i)
+			snd := make([]A, len(s)-i)
+
+			copy(fst, s[:i])
+			copy(snd, s[i:])
+
+			return fst, snd
+		}
+	}
+
+	res := make([]A, len(s))
+	copy(res, s)
+
+	return res, []A{}
+}
+
+// SplitAt(n, s) returns a tuple where first element is s prefix of length n
+// and second element is the remainder of the list.
+func SplitAt[A any](n uint, s []A) ([]A, []A) {
+	fst := make([]A, n)
+	snd := make([]A, len(s)-int(n))
+
+	copy(fst, s[:n])
+	copy(snd, s[n:])
+
+	return fst, snd
+}
+
+// ZipWith combines slice elements with the same index using the function
+// argument, returning a slice of the results.
+func ZipWith[A, B, C any](f func(A, B) C, a []A, b []B) []C {
+	var l uint
+
+	if la, lb := len(a), len(b); la < lb {
+		l = uint(la)
+	} else {
+		l = uint(lb)
+	}
+
+	res := make([]C, l)
+
+	for i := 0; i < int(l); i++ {
+		res[i] = f(a[i], b[i])
+	}
+
+	return res
+}

fn/slice_test.go

@@ -0,0 +1,138 @@
+package fn
+
+import (
+	"slices"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func even(a int) bool { return a%2 == 0 }
+func odd(a int) bool  { return a%2 != 0 }
+
+func TestAll(t *testing.T) {
+	x := []int{0, 2, 4, 6, 8}
+	require.True(t, All(even, x))
+	require.False(t, All(odd, x))
+
+	y := []int{1, 3, 5, 7, 9}
+	require.False(t, All(even, y))
+	require.True(t, All(odd, y))
+
+	z := []int{0, 2, 4, 6, 9}
+	require.False(t, All(even, z))
+	require.False(t, All(odd, z))
+}
+
+func TestAny(t *testing.T) {
+	x := []int{1, 3, 5, 7, 9}
+	require.False(t, Any(even, x))
+	require.True(t, Any(odd, x))
+
+	y := []int{0, 3, 5, 7, 9}
+	require.True(t, Any(even, y))
+	require.True(t, Any(odd, y))
+
+	z := []int{0, 2, 4, 6, 8}
+	require.True(t, Any(even, z))
+	require.False(t, Any(odd, z))
+}
+
+func TestMap(t *testing.T) {
+	inc := func(i int) int { return i + 1 }
+
+	x := []int{0, 2, 4, 6, 8}
+
+	y := Map(inc, x)
+
+	z := []int{1, 3, 5, 7, 9}
+
+	require.True(t, slices.Equal(y, z))
+}
+
+func TestFilter(t *testing.T) {
+	x := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
+
+	y := Filter(even, x)
+
+	require.True(t, All(even, y))
+
+	z := Filter(odd, y)
+
+	require.Zero(t, len(z))
+}
+
+func TestFoldl(t *testing.T) {
+	seed := []int{}
+	stupid := func(s []int, a int) []int { return append(s, a) }
+
+	x := []int{0, 1, 2, 3, 4}
+
+	r := Foldl(stupid, seed, x)
+
+	require.True(t, slices.Equal(x, r))
+}
+
+func TestFoldr(t *testing.T) {
+	seed := []int{}
+	stupid := func(a int, s []int) []int { return append(s, a) }
+
+	x := []int{0, 1, 2, 3, 4}
+
+	z := Foldr(stupid, seed, x)
+
+	slices.Reverse[[]int](x)
+
+	require.True(t, slices.Equal(x, z))
+}
+
+func TestFind(t *testing.T) {
+	x := []int{10, 11, 12, 13, 14, 15}
+
+	div3 := func(a int) bool { return a%3 == 0 }
+	div8 := func(a int) bool { return a%8 == 0 }
+
+	require.Equal(t, Find(div3, x), Some(12))
+
+	require.Equal(t, Find(div8, x), None[int]())
+}
+
+func TestFlatten(t *testing.T) {
+	x := [][]int{{0}, {1}, {2}}
+
+	y := Flatten(x)
+
+	require.True(t, slices.Equal(y, []int{0, 1, 2}))
+}
+
+func TestReplicate(t *testing.T) {
+	require.True(t, slices.Equal([]int{1, 1, 1, 1, 1}, Replicate(5, 1)))
+}
+
+func TestSpan(t *testing.T) {
+	x := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
+	lt5 := func(a int) bool { return a < 5 }
+
+	low, high := Span(lt5, x)
+
+	require.True(t, slices.Equal(low, []int{0, 1, 2, 3, 4}))
+	require.True(t, slices.Equal(high, []int{5, 6, 7, 8, 9}))
+}
+
+func TestSplitAt(t *testing.T) {
+	x := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
+	fst, snd := SplitAt(5, x)
+
+	require.True(t, slices.Equal(fst, []int{0, 1, 2, 3, 4}))
+	require.True(t, slices.Equal(snd, []int{5, 6, 7, 8, 9}))
+}
+
+func TestZipWith(t *testing.T) {
+	eq := func(a, b int) bool { return a == b }
+	x := []int{0, 1, 2, 3, 4}
+	y := Replicate(5, 1)
+	z := ZipWith(eq, x, y)
+	require.True(t, slices.Equal(
+		z, []bool{false, true, false, false, false},
+	))
+}