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feat(tvix/eval): Implement comparison for lists

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Lists are compared lexicographically in C++ nix as of [0], and our
updated nix test suites depend on this. This implements comparison of
list values in `Value::nix_cmp` using a very similar algorithm to what
C++ does - similarly to there, this requires passing in the VM so we can
force thunks in the list elements as we go.

[0]: 09471d2680#

Change-Id: I5d8bb07f90647a1fec83f775243e21af856afbb1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7070
Autosubmit: grfn <grfn@gws.fyi>
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
This commit is contained in:
Griffin Smith 2022-10-23 13:37:11 -04:00 • committed by tazjin
parent b8a7dba709
commit d0a836b0e1
7 changed files with 45 additions and 3 deletions
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15
tvix/eval/src/value/mod.rs
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@ -351,12 +351,25 @@ impl Value {
}
/// Compare `self` against other using (fallible) Nix ordering semantics.
pub fn nix_cmp(&self, other: &Self) -> Result<Option<Ordering>, ErrorKind> {
pub fn nix_cmp(&self, other: &Self, vm: &mut VM) -> Result<Option<Ordering>, ErrorKind> {
match (self, other) {
// same types
(Value::Integer(i1), Value::Integer(i2)) => Ok(i1.partial_cmp(i2)),
(Value::Float(f1), Value::Float(f2)) => Ok(f1.partial_cmp(f2)),
(Value::String(s1), Value::String(s2)) => Ok(s1.partial_cmp(s2)),
(Value::List(l1), Value::List(l2)) => {
for i in 0.. {
if i == l2.len() {
return Ok(Some(Ordering::Greater));
} else if i == l1.len() {
return Ok(Some(Ordering::Less));
} else if !l1[i].nix_eq(&l2[i], vm)? {
return l1[i].force(vm)?.nix_cmp(&*l2[i].force(vm)?, vm);
}
}
unreachable!()
}
// different types
(Value::Integer(i1), Value::Float(f2)) => Ok((*i1 as f64).partial_cmp(f2)),