26 lines
507 B
Plaintext
26 lines
507 B
Plaintext
pub fn foldr(xs: List<a>, f: fn(a, b) -> b, zero: b) -> b {
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when xs is {
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[] ->
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zero
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[x, ..rest] ->
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f(x, foldr(rest, f, zero))
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}
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}
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pub fn concat(left: List<a>, right: List<a>) -> List<a> {
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foldr(left, fn(x, xs) { [x, ..xs] }, right)
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}
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pub fn flat_map(xs: List<a>, f: fn(a) -> List<b>) -> List<b> {
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when xs is {
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[] ->
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[]
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[x, ..rest] ->
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concat(f(x), flat_map(rest, f))
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}
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}
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test flat_map_2() {
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flat_map([1, 2, 3], fn(a) { [a, a] }) == [1, 1, 2, 2, 3, 3]
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}
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