mozilla/rust — Issue #1528: Functions written in expression style are slower than imperative.
Author: brson
Created: 2012-01-15 03:35:56+00:00
State: open
Labels: bug, perf, trans

This takes 4.7s:

```
use std;

fn ack(m: int, n: int) -> int {
if m == 0 {
ret n + 1
} else {
if n == 0 {
ret ack(m - 1, 1)
} else {
ret ack(m - 1, ack(m, n - 1));
}
}
}

fn main(args: [str]) {
// FIXME: #1527
sys::set_min_stack(1000000u);
let n = if vec::len(args) == 2u {
int::from_str(args[1])
} else {
12
};
std::io::println(#fmt("Ack(3,%d): %d\n", n, ack(3, n)));
}
```

This takes 5.5:

```
use std;

fn ack(m: int, n: int) -> int {
if m == 0 {
n + 1
} else {
if n == 0 {
ack(m - 1, 1)
} else {
ack(m - 1, ack(m, n - 1))
}
}
}

fn main(args: [str]) {
// FIXME: #1527
sys::set_min_stack(1000000u);
let n = if vec::len(args) == 2u {
int::from_str(args[1])
} else {
12
};
std::io::println(#fmt("Ack(3,%d): %d\n", n, ack(3, n)));
}
```