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pkg/list: adding flatten function as a builtin
this commit adds a new builtin to the list package for generating a
flat list from a nested lists by expanding nested lists in place.
for instance
list.Flatten([1, [[2, 3], []], [4]])
results in
[1, 2, 3, 4]
Change-Id: Ia462f7f2db504fd49601a3c77c0fae9387c038c4
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/3460
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
authored by
xinau
and committed by
Marcel van Lohuizen
074cf5de
22a42d4c
+73
+6
cue/builtin_test.go
+6
cue/builtin_test.go
···
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test("list", `list.Drop([1, 2, 3, 4], -1)`),
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`_|_(error in call to list.Drop: negative index)`,
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}, {
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+
test("list", `list.Flatten([1, [[2, 3], []], [4]])`),
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`[1,2,3,4]`,
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}, {
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test("list", `list.Flatten("foo")`),
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`_|_(error in call to list.Flatten: cannot use value "foo" (type string) as list)`,
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}, {
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test("list", `list.Max([1, 2, 3, 4])`),
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`4`,
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}, {
+31
cue/builtins.go
+31
cue/builtins.go
···
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}()
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},
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}, {
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Name: "Flatten",
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Params: []kind{topKind},
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Result: listKind,
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Func: func(c *callCtxt) {
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xs := c.value(0)
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c.ret, c.err = func() (interface{}, error) {
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var flatten func(Value) ([]Value, error)
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flatten = func(xs Value) ([]Value, error) {
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var res []Value
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iter, err := xs.List()
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if err != nil {
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return nil, err
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}
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for iter.Next() {
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val := iter.Value()
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if val.Kind() == ListKind {
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vals, err := flatten(val)
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+
if err != nil {
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return nil, err
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}
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res = append(res, vals...)
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} else {
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res = append(res, val)
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}
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}
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return res, nil
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}
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return flatten(xs)
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}()
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},
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}, {
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Name: "Take",
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Params: []kind{listKind, intKind},
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Result: listKind,
+36
pkg/list/list.go
+36
pkg/list/list.go
···
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return x[n:], nil
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}
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// Flatten reports a flattend sequence of the list x by expanding any elements
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// that are lists.
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//
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// For instance:
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//
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// Flatten([1, [[2, 3], []], [4]])
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//
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// results in
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//
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// [1, 2, 3, 4]
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//
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func Flatten(xs cue.Value) ([]cue.Value, error) {
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var flatten func(cue.Value) ([]cue.Value, error)
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flatten = func(xs cue.Value) ([]cue.Value, error) {
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var res []cue.Value
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iter, err := xs.List()
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if err != nil {
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return nil, err
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}
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for iter.Next() {
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val := iter.Value()
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if val.Kind() == cue.ListKind {
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vals, err := flatten(val)
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if err != nil {
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return nil, err
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}
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res = append(res, vals...)
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} else {
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res = append(res, val)
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}
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}
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return res, nil
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}
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return flatten(xs)
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}
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+
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// Take reports the prefix of length n of list x, or x itself if n > len(x).
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//
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// For instance: