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authorVincent Ambo <mail@tazj.in>2022-09-23T00·14+0300
committertazjin <tazjin@tvl.su>2022-09-23T09·55+0000
commitf816813d41271043473f8740bbc8c257f9b54982 (patch)
treec75bf935076036c131d40958026f3a220319a2e3 /tvix/eval/src/builtins
parent1015f2f8e7c37c5c4b4ebca799579c5f6c0d5100 (diff)
feat(tvix/eval): implement 'builtins.filter' r/4963
This is a little ugly because the plain Iterator::filter method can
not be used (it does not support fallible primitives), so we need to
resort to an `Iterator::filter_map` and deal with the wrapping in
Options everywhere.

This prevents use of `?` which introduces the need for some matching,
but it's not *too* bad.

Change-Id: Ie2c3c0c9756c4c627176f64fb4e0054e717c26d1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6765
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Diffstat (limited to 'tvix/eval/src/builtins')
-rw-r--r--tvix/eval/src/builtins/mod.rs29
1 files changed, 29 insertions, 0 deletions
diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 872033648aff..17094a6f9452 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -132,6 +132,35 @@ fn pure_builtins() -> Vec<Builtin> {
                 }
             }
         }),
+        Builtin::new("filter", &[true, true], |args, vm| {
+            let list: NixList = args[1].to_list()?;
+
+            list.into_iter()
+                .filter_map(|elem| {
+                    vm.push(elem.clone());
+
+                    let result = match vm.call_value(&args[0]) {
+                        Err(err) => return Some(Err(err)),
+                        Ok(result) => result,
+                    };
+
+                    // Must be assigned to a local to avoid a borrowcheck
+                    // failure related to the ForceResult destructor.
+                    let result = match result.force(vm) {
+                        Err(err) => Some(Err(vm.error(err))),
+                        Ok(value) => match value.as_bool() {
+                            Ok(true) => Some(Ok(elem)),
+                            Ok(false) => None,
+                            Err(err) => Some(Err(vm.error(err))),
+                        },
+                    };
+
+                    result
+                })
+                .collect::<Result<Vec<Value>, _>>()
+                .map(|list| Value::List(NixList::from(list)))
+                .map_err(Into::into)
+        }),
         Builtin::new("getAttr", &[true, true], |args, _| {
             let k = args[0].to_str()?;
             let xs = args[1].to_attrs()?;