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list.go
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list.go
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// Copyright 2019 CUE Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package list contains functions for manipulating and examining lists.
package list
import (
"fmt"
"sort"
"cuelang.org/go/cue"
)
// Drop reports the suffix of list x after the first n elements,
// or [] if n > len(x).
//
// For instance:
//
// Drop([1, 2, 3, 4], 2)
//
// results in
//
// [3, 4]
//
func Drop(x []cue.Value, n int) ([]cue.Value, error) {
if n < 0 {
return nil, fmt.Errorf("negative index")
}
if n > len(x) {
return []cue.Value{}, nil
}
return x[n:], nil
}
// TODO: disable Flatten until we know the right default for depth.
// The right time to determine is at least some point after the query
// extensions are introduced, which may provide flatten functionality
// natively.
//
// // Flatten reports a flattend sequence of the list xs by expanding any elements
// // that are lists.
// //
// // For instance:
// //
// // Flatten([1, [[2, 3], []], [4]])
// //
// // results in
// //
// // [1, 2, 3, 4]
// //
// func Flatten(xs cue.Value) ([]cue.Value, error) {
// var flatten func(cue.Value) ([]cue.Value, error)
// flatten = func(xs cue.Value) ([]cue.Value, error) {
// var res []cue.Value
// iter, err := xs.List()
// if err != nil {
// return nil, err
// }
// for iter.Next() {
// val := iter.Value()
// if val.Kind() == cue.ListKind {
// vals, err := flatten(val)
// if err != nil {
// return nil, err
// }
// res = append(res, vals...)
// } else {
// res = append(res, val)
// }
// }
// return res, nil
// }
// return flatten(xs)
// }
// FlattenN reports a flattend sequence of the list xs by expanding any elements
// depth levels deep. If depth is negative all elements are expanded.
//
// For instance:
//
// FlattenN([1, [[2, 3], []], [4]], 1)
//
// results in
//
// [1, [2, 3], [], 4]
//
func FlattenN(xs cue.Value, depth int) ([]cue.Value, error) {
var flattenN func(cue.Value, int) ([]cue.Value, error)
flattenN = func(xs cue.Value, depth int) ([]cue.Value, error) {
var res []cue.Value
iter, err := xs.List()
if err != nil {
return nil, err
}
for iter.Next() {
val, _ := iter.Value().Default()
if val.Kind() == cue.ListKind && depth != 0 {
d := depth - 1
values, err := flattenN(val, d)
if err != nil {
return nil, err
}
res = append(res, values...)
} else {
res = append(res, val)
}
}
return res, nil
}
return flattenN(xs, depth)
}
// Repeat returns a new list consisting of count copies of list x.
//
// For instance:
//
// Repeat([1, 2], 2)
//
// results in
//
// [1, 2, 1, 2]
//
func Repeat(x []cue.Value, count int) ([]cue.Value, error) {
if count < 0 {
return nil, fmt.Errorf("negative count")
}
var a []cue.Value
for i := 0; i < count; i++ {
a = append(a, x...)
}
return a, nil
}
// Concat takes a list of lists and concatenates them.
//
// Concat([a, b, c]) is equivalent to
//
// [ for x in a {x}, for x in b {x}, for x in c {x} ]
//
func Concat(a []cue.Value) ([]cue.Value, error) {
var res []cue.Value
for _, e := range a {
iter, err := e.List()
if err != nil {
return nil, err
}
for iter.Next() {
res = append(res, iter.Value())
}
}
return res, nil
}
// Take reports the prefix of length n of list x, or x itself if n > len(x).
//
// For instance:
//
// Take([1, 2, 3, 4], 2)
//
// results in
//
// [1, 2]
//
func Take(x []cue.Value, n int) ([]cue.Value, error) {
if n < 0 {
return nil, fmt.Errorf("negative index")
}
if n > len(x) {
return x, nil
}
return x[:n], nil
}
// Slice extracts the consecutive elements from list x starting from position i
// up till, but not including, position j, where 0 <= i < j <= len(x).
//
// For instance:
//
// Slice([1, 2, 3, 4], 1, 3)
//
// results in
//
// [2, 3]
//
func Slice(x []cue.Value, i, j int) ([]cue.Value, error) {
if i < 0 {
return nil, fmt.Errorf("negative index")
}
if i > j {
return nil, fmt.Errorf("invalid index: %v > %v", i, j)
}
if i > len(x) {
return nil, fmt.Errorf("slice bounds out of range")
}
if j > len(x) {
return nil, fmt.Errorf("slice bounds out of range")
}
return x[i:j], nil
}
// MinItems reports whether a has at least n items.
func MinItems(a []cue.Value, n int) bool {
return len(a) >= n
}
// MaxItems reports whether a has at most n items.
func MaxItems(a []cue.Value, n int) bool {
return len(a) <= n
}
// UniqueItems reports whether all elements in the list are unique.
func UniqueItems(a []cue.Value) bool {
b := []string{}
for _, v := range a {
b = append(b, fmt.Sprintf("%+v", v))
}
sort.Strings(b)
for i := 1; i < len(b); i++ {
if b[i-1] == b[i] {
return false
}
}
return true
}
// Contains reports whether v is contained in a. The value must be a
// comparable value.
func Contains(a []cue.Value, v cue.Value) bool {
for _, w := range a {
if v.Equals(w) {
return true
}
}
return false
}