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36 lines
1.2 KiB
Rust
36 lines
1.2 KiB
Rust
//@ revisions: become return
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//@ [become] run-pass
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#![allow(incomplete_features)]
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#![feature(explicit_tail_calls)]
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// This is an identity function (`|x| x`), but implemented using recursion.
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// Each step we increment accumulator and decrement the number.
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//
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// With normal calls this fails compilation because of the recursion limit,
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// but with tail calls/`become` we don't grow the stack/spend recursion limit
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// so this should compile.
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const fn rec_id(n: u32) -> u32 {
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const fn inner(acc: u32, n: u32) -> u32 {
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match n {
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0 => acc,
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#[cfg(r#become)] _ => become inner(acc + 1, n - 1),
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#[cfg(r#return)] _ => return inner(acc + 1, n - 1),
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//[return]~^ error: evaluation of constant value failed
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}
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}
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inner(0, n)
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}
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// Some relatively big number that is higher than recursion limit
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const ORIGINAL: u32 = 12345;
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// Original number, but with identity function applied
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// (this is the same, but requires execution of the recursion)
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const ID_ED: u32 = rec_id(ORIGINAL);
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// Assert to make absolutely sure the computation actually happens
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const ASSERT: () = assert!(ORIGINAL == ID_ED);
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fn main() {
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let _ = ASSERT;
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}
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