4 files changed, 43 insertions, 1 deletions
diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index dfc1986141..598c8aa08e 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -12,7 +12,8 @@ use std::{
 
 use crate::{
     errors::ErrorKind,
-    value::{Builtin, CoercionKind, NixAttrs, NixList, NixString, Value},
+    upvalues::UpvalueCarrier,
+    value::{Builtin, Closure, CoercionKind, NixAttrs, NixList, NixString, Value},
     vm::VM,
 };
 
@@ -144,6 +145,21 @@ fn pure_builtins() -> Vec<Builtin> {
         Builtin::new("length", &[true], |args, _| {
             Ok(Value::Integer(args[0].to_list()?.len() as i64))
         }),
+        Builtin::new("map", &[true, true], |args, vm| {
+            let list: NixList = args[1].to_list()?;
+            let func: Closure = args[0].to_closure()?;
+
+            list.into_iter()
+                .map(|val| {
+                    // Leave the argument on the stack before calling the
+                    // function.
+                    vm.push(val);
+                    vm.call(func.lambda(), func.upvalues().clone(), 1)
+                })
+                .collect::<Result<Vec<Value>, _>>()
+                .map(|list| Value::List(NixList::from(list)))
+                .map_err(Into::into)
+        }),
         Builtin::new("hasAttr", &[true, true], |args, _| {
             let k = args[0].to_str()?;
             let xs = args[1].to_attrs()?;
diff --git a/tvix/eval/src/errors.rs b/tvix/eval/src/errors.rs
index 10bc9276ad..17b236d038 100644
--- a/tvix/eval/src/errors.rs
+++ b/tvix/eval/src/errors.rs
@@ -100,6 +100,15 @@ impl From<ParseIntError> for ErrorKind {
     }
 }
 
+/// Implementation used if errors occur while forcing thunks (which
+/// can potentially be threaded through a few contexts, i.e. nested
+/// thunks).
+impl From<Error> for ErrorKind {
+    fn from(e: Error) -> Self {
+        Self::ThunkForce(Box::new(e))
+    }
+}
+
 #[derive(Clone, Debug)]
 pub struct Error {
     pub kind: ErrorKind,
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map.exp
new file mode 100644
index 0000000000..e1ff708002
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map.exp
@@ -0,0 +1 @@
+[ [ 1 2 3 4 5 ] [ 2 4 6 8 10 ] [ 2 4 6 8 10 ] [ 1 2 3 4 5 ] ]
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map.nix
new file mode 100644
index 0000000000..6ff42d0891
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map.nix
@@ -0,0 +1,16 @@
+[
+  # identity function
+  (builtins.map (x: x) [ 1 2 3 4 5 ])
+
+  # double stuff
+  (builtins.map (x: x * 2) [ 1 2 3 4 5 ])
+
+  # same but with a closure this time
+  (
+    let n = 2;
+    in builtins.map (x: x * n) [ 1 2 3 4 5 ]
+  )
+
+  # from global scope
+  (map (x: x) [ 1 2 3 4 5 ])
+]