refactor(tvix/eval): Define *all* pure builtins at the top-level r/5265

Break out all pure builtin functions to top-level functions defined
within the `pure_builtins` module in `builtins/mod.rs`.

Change-Id: I9a10660446d557b1a86da4c45a463e9a1a9b4f2d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7201
Reviewed-by: tazjin <tazjin@tvl.su>
Reviewed-by: Adam Joseph <adam@westernsemico.com>
Tested-by: BuildkiteCI

1 files changed, 792 insertions, 728 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 0ae43e3d38..caa575fcf3 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -59,781 +59,845 @@ mod pure_builtins {
     fn builtin_abort(_vm: &mut VM, message: Value) -> Result<Value, ErrorKind> {
         Err(ErrorKind::Abort(message.to_str()?.to_string()))
     }
-}
 
-/// Return all pure builtins, that is all builtins that do not rely on
-/// I/O outside of the VM and which can be used in any contexts (e.g.
-/// WASM).
-fn pure_builtins() -> Vec<Builtin> {
-    let mut bs = vec![
-        Builtin::new(
-            "add",
-            &[false, false],
-            |args: Vec<Value>, vm: &mut VM| arithmetic_op!(&*args[0].force(vm)?, &*args[1].force(vm)?, +),
-        ),
-        Builtin::new("all", &[true, true], |args: Vec<Value>, vm: &mut VM| {
-            for value in args[1].to_list()?.into_iter() {
-                let pred_result = vm.call_with(&args[0], [value])?;
+    #[builtin("add")]
+    fn builtin_add(vm: &mut VM, #[lazy] x: Value, #[lazy] y: Value) -> Result<Value, ErrorKind> {
+        arithmetic_op!(&*x.force(vm)?, &*y.force(vm)?, +)
+    }
 
-                if !pred_result.force(vm)?.as_bool()? {
-                    return Ok(Value::Bool(false));
-                }
+    #[builtin("all")]
+    fn builtin_all(vm: &mut VM, pred: Value, list: Value) -> Result<Value, ErrorKind> {
+        for value in list.to_list()?.into_iter() {
+            let pred_result = vm.call_with(&pred, [value])?;
+
+            if !pred_result.force(vm)?.as_bool()? {
+                return Ok(Value::Bool(false));
             }
+        }
 
-            Ok(Value::Bool(true))
-        }),
-        Builtin::new("any", &[true, true], |args: Vec<Value>, vm: &mut VM| {
-            for value in args[1].to_list()?.into_iter() {
-                let pred_result = vm.call_with(&args[0], [value])?;
+        Ok(Value::Bool(true))
+    }
 
-                if pred_result.force(vm)?.as_bool()? {
-                    return Ok(Value::Bool(true));
-                }
+    #[builtin("any")]
+    fn builtin_any(vm: &mut VM, pred: Value, list: Value) -> Result<Value, ErrorKind> {
+        for value in list.to_list()?.into_iter() {
+            let pred_result = vm.call_with(&pred, [value])?;
+
+            if pred_result.force(vm)?.as_bool()? {
+                return Ok(Value::Bool(true));
             }
+        }
 
-            Ok(Value::Bool(false))
-        }),
-        Builtin::new("attrNames", &[true], |args: Vec<Value>, _: &mut VM| {
-            let xs = args[0].to_attrs()?;
-            let mut output = Vec::with_capacity(xs.len());
+        Ok(Value::Bool(false))
+    }
 
-            for (key, _val) in xs.iter() {
-                output.push(Value::String(key.clone()));
-            }
+    #[builtin("attrNames")]
+    fn builtin_attr_names(_: &mut VM, set: Value) -> Result<Value, ErrorKind> {
+        let xs = set.to_attrs()?;
+        let mut output = Vec::with_capacity(xs.len());
 
-            Ok(Value::List(NixList::construct(output.len(), output)))
-        }),
-        Builtin::new("attrValues", &[true], |args: Vec<Value>, _: &mut VM| {
-            let xs = args[0].to_attrs()?;
-            let mut output = Vec::with_capacity(xs.len());
+        for (key, _val) in xs.iter() {
+            output.push(Value::String(key.clone()));
+        }
+
+        Ok(Value::List(NixList::construct(output.len(), output)))
+    }
 
-            for (_key, val) in xs.iter() {
-                output.push(val.clone());
+    #[builtin("attrValues")]
+    fn builtin_attr_values(_: &mut VM, set: Value) -> Result<Value, ErrorKind> {
+        let xs = set.to_attrs()?;
+        let mut output = Vec::with_capacity(xs.len());
+
+        for (_key, val) in xs.iter() {
+            output.push(val.clone());
+        }
+
+        Ok(Value::List(NixList::construct(output.len(), output)))
+    }
+
+    #[builtin("baseNameOf")]
+    fn builtin_base_name_of(vm: &mut VM, s: Value) -> Result<Value, ErrorKind> {
+        let s = s.coerce_to_string(CoercionKind::Weak, vm)?;
+        let result: String = s.rsplit_once('/').map(|(_, x)| x).unwrap_or(&s).into();
+        Ok(result.into())
+    }
+
+    #[builtin("bitAnd")]
+    fn builtin_bit_and(_: &mut VM, x: Value, y: Value) -> Result<Value, ErrorKind> {
+        Ok(Value::Integer(x.as_int()? & y.as_int()?))
+    }
+
+    #[builtin("bitOr")]
+    fn builtin_bit_or(_: &mut VM, x: Value, y: Value) -> Result<Value, ErrorKind> {
+        Ok(Value::Integer(x.as_int()? | y.as_int()?))
+    }
+
+    #[builtin("bitXor")]
+    fn builtin_bit_xor(_: &mut VM, x: Value, y: Value) -> Result<Value, ErrorKind> {
+        Ok(Value::Integer(x.as_int()? ^ y.as_int()?))
+    }
+
+    #[builtin("catAttrs")]
+    fn builtin_cat_attrs(vm: &mut VM, key: Value, list: Value) -> Result<Value, ErrorKind> {
+        let key = key.to_str()?;
+        let list = list.to_list()?;
+        let mut output = vec![];
+
+        for item in list.into_iter() {
+            let set = item.force(vm)?.to_attrs()?;
+            if let Some(value) = set.select(key.as_str()) {
+                output.push(value.clone());
             }
+        }
 
-            Ok(Value::List(NixList::construct(output.len(), output)))
-        }),
-        Builtin::new("baseNameOf", &[true], |args: Vec<Value>, vm: &mut VM| {
-            let s = args[0].coerce_to_string(CoercionKind::Weak, vm)?;
-            let result: String = s.rsplit_once('/').map(|(_, x)| x).unwrap_or(&s).into();
-            Ok(result.into())
-        }),
-        Builtin::new("bitAnd", &[true, true], |args: Vec<Value>, _: &mut VM| {
-            Ok(Value::Integer(args[0].as_int()? & args[1].as_int()?))
-        }),
-        Builtin::new("bitOr", &[true, true], |args: Vec<Value>, _: &mut VM| {
-            Ok(Value::Integer(args[0].as_int()? | args[1].as_int()?))
-        }),
-        Builtin::new("bitXor", &[true, true], |args: Vec<Value>, _: &mut VM| {
-            Ok(Value::Integer(args[0].as_int()? ^ args[1].as_int()?))
-        }),
-        Builtin::new(
-            "catAttrs",
-            &[true, true],
-            |args: Vec<Value>, vm: &mut VM| {
-                let key = args[0].to_str()?;
-                let list = args[1].to_list()?;
-                let mut output = vec![];
-
-                for item in list.into_iter() {
-                    let set = item.force(vm)?.to_attrs()?;
-                    if let Some(value) = set.select(key.as_str()) {
-                        output.push(value.clone());
-                    }
-                }
+        Ok(Value::List(NixList::construct(output.len(), output)))
+    }
 
-                Ok(Value::List(NixList::construct(output.len(), output)))
-            },
-        ),
-        Builtin::new("ceil", &[true], |args: Vec<Value>, _: &mut VM| {
-            Ok(Value::Integer(args[0].as_float()?.ceil() as i64))
-        }),
-        Builtin::new(
-            "compareVersions",
-            &[true, true],
-            |args: Vec<Value>, _: &mut VM| {
-                let s1 = args[0].to_str()?;
-                let s1 = VersionPartsIter::new_for_cmp(s1.as_str());
-                let s2 = args[1].to_str()?;
-                let s2 = VersionPartsIter::new_for_cmp(s2.as_str());
-
-                match s1.cmp(s2) {
-                    std::cmp::Ordering::Less => Ok(Value::Integer(-1)),
-                    std::cmp::Ordering::Equal => Ok(Value::Integer(0)),
-                    std::cmp::Ordering::Greater => Ok(Value::Integer(1)),
-                }
-            },
-        ),
-        Builtin::new("concatLists", &[true], |args: Vec<Value>, vm: &mut VM| {
-            let list = args[0].to_list()?;
-            let lists = list
-                .into_iter()
-                .map(|elem| {
-                    let value = elem.force(vm)?;
-                    value.to_list()
-                })
-                .collect::<Result<Vec<NixList>, ErrorKind>>()?;
+    #[builtin("ceil")]
+    fn builtin_ceil(_: &mut VM, double: Value) -> Result<Value, ErrorKind> {
+        Ok(Value::Integer(double.as_float()?.ceil() as i64))
+    }
 
-            Ok(Value::List(NixList::from(
-                lists.into_iter().flatten().collect::<Vec<Value>>(),
-            )))
-        }),
-        Builtin::new(
-            "concatMap",
-            &[true, true],
-            |args: Vec<Value>, vm: &mut VM| {
-                let list = args[1].to_list()?;
-                let mut res = Vec::new();
-                for val in list {
-                    res.extend(vm.call_with(&args[0], [val])?.force(vm)?.to_list()?);
-                }
-                Ok(Value::List(res.into()))
-            },
-        ),
-        Builtin::new(
-            "concatStringsSep",
-            &[true, true],
-            |args: Vec<Value>, vm: &mut VM| {
-                let separator = args[0].to_str()?;
-                let list = args[1].to_list()?;
-                let mut res = String::new();
-                for (i, val) in list.into_iter().enumerate() {
-                    if i != 0 {
-                        res.push_str(&separator);
-                    }
-                    res.push_str(&val.force(vm)?.coerce_to_string(CoercionKind::Weak, vm)?);
-                }
-                Ok(res.into())
-            },
-        ),
-        Builtin::new(
-            "deepSeq",
-            &[true, true],
-            |mut args: Vec<Value>, vm: &mut VM| {
-                let arg2 = args.pop().unwrap();
-                let arg1 = args.pop().unwrap();
-                arg1.deep_force(vm, &mut Default::default())?;
-                Ok(arg2)
-            },
-        ),
-        Builtin::new(
-            "div",
-            &[false, false],
-            |args: Vec<Value>, vm: &mut VM| arithmetic_op!(&*args[0].force(vm)?, &*args[1].force(vm)?, /),
-        ),
-        Builtin::new("dirOf", &[true], |args: Vec<Value>, vm: &mut VM| {
-            let s = args[0].coerce_to_string(CoercionKind::Weak, vm)?;
-            let result = s
-                .rsplit_once('/')
-                .map(|(x, _)| match x {
-                    "" => "/",
-                    _ => x,
-                })
-                .unwrap_or(".");
-            if args[0].is_path() {
-                Ok(Value::Path(result.into()))
-            } else {
-                Ok(result.into())
+    #[builtin("compareVersions")]
+    fn builtin_compare_versions(_: &mut VM, x: Value, y: Value) -> Result<Value, ErrorKind> {
+        let s1 = x.to_str()?;
+        let s1 = VersionPartsIter::new_for_cmp(s1.as_str());
+        let s2 = y.to_str()?;
+        let s2 = VersionPartsIter::new_for_cmp(s2.as_str());
+
+        match s1.cmp(s2) {
+            std::cmp::Ordering::Less => Ok(Value::Integer(-1)),
+            std::cmp::Ordering::Equal => Ok(Value::Integer(0)),
+            std::cmp::Ordering::Greater => Ok(Value::Integer(1)),
+        }
+    }
+
+    #[builtin("concatLists")]
+    fn builtin_concat_lists(vm: &mut VM, lists: Value) -> Result<Value, ErrorKind> {
+        let list = lists.to_list()?;
+        let lists = list
+            .into_iter()
+            .map(|elem| {
+                let value = elem.force(vm)?;
+                value.to_list()
+            })
+            .collect::<Result<Vec<NixList>, ErrorKind>>()?;
+
+        Ok(Value::List(NixList::from(
+            lists.into_iter().flatten().collect::<Vec<Value>>(),
+        )))
+    }
+
+    #[builtin("concatMap")]
+    fn builtin_concat_map(vm: &mut VM, f: Value, list: Value) -> Result<Value, ErrorKind> {
+        let list = list.to_list()?;
+        let mut res = Vec::new();
+        for val in list {
+            res.extend(vm.call_with(&f, [val])?.force(vm)?.to_list()?);
+        }
+        Ok(Value::List(res.into()))
+    }
+
+    #[builtin("concatStringsSep")]
+    fn builtin_concat_strings_sep(
+        vm: &mut VM,
+        separator: Value,
+        list: Value,
+    ) -> Result<Value, ErrorKind> {
+        let separator = separator.to_str()?;
+        let list = list.to_list()?;
+        let mut res = String::new();
+        for (i, val) in list.into_iter().enumerate() {
+            if i != 0 {
+                res.push_str(&separator);
             }
-        }),
-        Builtin::new("elem", &[true, true], |args: Vec<Value>, vm: &mut VM| {
-            for val in args[1].to_list()? {
-                if val.nix_eq(&args[0], vm)? {
-                    return Ok(true.into());
-                }
+            res.push_str(&val.force(vm)?.coerce_to_string(CoercionKind::Weak, vm)?);
+        }
+        Ok(res.into())
+    }
+
+    #[builtin("deepSeq")]
+    fn builtin_deep_seq(vm: &mut VM, x: Value, y: Value) -> Result<Value, ErrorKind> {
+        x.deep_force(vm, &mut Default::default())?;
+        Ok(y)
+    }
+
+    #[builtin("div")]
+    fn builtin_div(vm: &mut VM, #[lazy] x: Value, #[lazy] y: Value) -> Result<Value, ErrorKind> {
+        arithmetic_op!(&*x.force(vm)?, &*y.force(vm)?, /)
+    }
+
+    #[builtin("dirOf")]
+    fn builtin_dir_of(vm: &mut VM, s: Value) -> Result<Value, ErrorKind> {
+        let str = s.coerce_to_string(CoercionKind::Weak, vm)?;
+        let result = str
+            .rsplit_once('/')
+            .map(|(x, _)| match x {
+                "" => "/",
+                _ => x,
+            })
+            .unwrap_or(".");
+        if s.is_path() {
+            Ok(Value::Path(result.into()))
+        } else {
+            Ok(result.into())
+        }
+    }
+
+    #[builtin("elem")]
+    fn builtin_elem(vm: &mut VM, x: Value, xs: Value) -> Result<Value, ErrorKind> {
+        for val in xs.to_list()? {
+            if val.nix_eq(&x, vm)? {
+                return Ok(true.into());
             }
-            Ok(false.into())
-        }),
-        Builtin::new("elemAt", &[true, true], |args: Vec<Value>, _: &mut VM| {
-            let xs = args[0].to_list()?;
-            let i = args[1].as_int()?;
-            if i < 0 {
-                Err(ErrorKind::IndexOutOfBounds { index: i })
-            } else {
-                match xs.get(i as usize) {
-                    Some(x) => Ok(x.clone()),
-                    None => Err(ErrorKind::IndexOutOfBounds { index: i }),
-                }
+        }
+        Ok(false.into())
+    }
+
+    #[builtin("elemAt")]
+    fn builtin_elem_at(_: &mut VM, xs: Value, i: Value) -> Result<Value, ErrorKind> {
+        let xs = xs.to_list()?;
+        let i = i.as_int()?;
+        if i < 0 {
+            Err(ErrorKind::IndexOutOfBounds { index: i })
+        } else {
+            match xs.get(i as usize) {
+                Some(x) => Ok(x.clone()),
+                None => Err(ErrorKind::IndexOutOfBounds { index: i }),
             }
-        }),
-        Builtin::new("filter", &[true, true], |args: Vec<Value>, vm: &mut VM| {
-            let list: NixList = args[1].to_list()?;
-
-            list.into_iter()
-                .filter_map(|elem| {
-                    let result = match vm.call_with(&args[0], [elem.clone()]) {
-                        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) {
+        }
+    }
+
+    #[builtin("filter")]
+    fn builtin_filter(vm: &mut VM, pred: Value, list: Value) -> Result<Value, ErrorKind> {
+        let list: NixList = list.to_list()?;
+
+        list.into_iter()
+            .filter_map(|elem| {
+                let result = match vm.call_with(&pred, [elem.clone()]) {
+                    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))),
-                        Ok(value) => match value.as_bool() {
-                            Ok(true) => Some(Ok(elem)),
-                            Ok(false) => None,
-                            Err(err) => Some(Err(vm.error(err))),
-                        },
-                    };
-
-                    result
+                    },
+                };
+
+                result
+            })
+            .collect::<Result<Vec<Value>, _>>()
+            .map(|list| Value::List(NixList::from(list)))
+            .map_err(Into::into)
+    }
+
+    #[builtin("floor")]
+    fn builtin_floor(_: &mut VM, double: Value) -> Result<Value, ErrorKind> {
+        Ok(Value::Integer(double.as_float()?.floor() as i64))
+    }
+
+    #[builtin("foldl'")]
+    fn builtin_foldl(
+        vm: &mut VM,
+        op: Value,
+        #[lazy] mut nul: Value,
+        list: Value,
+    ) -> Result<Value, ErrorKind> {
+        let list = list.to_list()?;
+        for val in list {
+            nul = vm.call_with(&op, [nul, val])?;
+            nul.force(vm)?;
+        }
+
+        Ok(nul)
+    }
+
+    #[builtin("functionArgs")]
+    fn builtin_function_args(_: &mut VM, f: Value) -> Result<Value, ErrorKind> {
+        let lambda = f.to_closure()?.lambda();
+        let formals = if let Some(formals) = &lambda.formals {
+            formals
+        } else {
+            return Ok(Value::attrs(NixAttrs::empty()));
+        };
+        Ok(Value::attrs(NixAttrs::from_map(
+            formals
+                .arguments
+                .iter()
+                .map(|(k, v)| (k.clone(), (*v).into()))
+                .collect(),
+        )))
+    }
+
+    #[builtin("fromJSON")]
+    fn builtin_from_json(_: &mut VM, json: Value) -> Result<Value, ErrorKind> {
+        let json_str = json.to_str()?;
+        let json: serde_json::Value = serde_json::from_str(&json_str)?;
+        json.try_into()
+    }
+
+    #[builtin("genList")]
+    fn builtin_gen_list(vm: &mut VM, generator: Value, length: Value) -> Result<Value, ErrorKind> {
+        let len = length.as_int()?;
+        (0..len)
+            .map(|i| vm.call_with(&generator, [i.into()]))
+            .collect::<Result<Vec<Value>, _>>()
+            .map(|list| Value::List(NixList::from(list)))
+            .map_err(Into::into)
+    }
+
+    #[builtin("getAttr")]
+    fn builtin_get_attr(_: &mut VM, key: Value, set: Value) -> Result<Value, ErrorKind> {
+        let k = key.to_str()?;
+        let xs = set.to_attrs()?;
+
+        match xs.select(k.as_str()) {
+            Some(x) => Ok(x.clone()),
+            None => Err(ErrorKind::AttributeNotFound {
+                name: k.to_string(),
+            }),
+        }
+    }
+
+    #[builtin("groupBy")]
+    fn builtin_group_by(vm: &mut VM, f: Value, list: Value) -> Result<Value, ErrorKind> {
+        let mut res: BTreeMap<NixString, Value> = BTreeMap::new();
+        for val in list.to_list()? {
+            let key = vm.call_with(&f, [val.clone()])?.force(vm)?.to_str()?;
+            res.entry(key)
+                .or_insert_with(|| Value::List(NixList::new()))
+                .as_list_mut()?
+                .push(val);
+        }
+        Ok(Value::attrs(NixAttrs::from_map(res)))
+    }
+
+    #[builtin("hasAttr")]
+    fn builtin_has_attr(_: &mut VM, key: Value, set: Value) -> Result<Value, ErrorKind> {
+        let k = key.to_str()?;
+        let xs = set.to_attrs()?;
+
+        Ok(Value::Bool(xs.contains(k.as_str())))
+    }
+
+    #[builtin("head")]
+    fn builtin_head(_: &mut VM, list: Value) -> Result<Value, ErrorKind> {
+        match list.to_list()?.get(0) {
+            Some(x) => Ok(x.clone()),
+            None => Err(ErrorKind::IndexOutOfBounds { index: 0 }),
+        }
+    }
+
+    #[builtin("intersectAttrs")]
+    fn builtin_intersect_attrs(_: &mut VM, x: Value, y: Value) -> Result<Value, ErrorKind> {
+        let mut res = BTreeMap::new();
+        let attrs1 = x.to_attrs()?;
+        let attrs2 = y.to_attrs()?;
+        for (k, v) in attrs2.iter() {
+            if attrs1.contains(k) {
+                res.insert(k.clone(), v.clone());
+            }
+        }
+        Ok(Value::attrs(NixAttrs::from_map(res)))
+    }
+
+    // For `is*` predicates we force manually, as Value::force also unwraps any Thunks
+
+    #[builtin("isAttrs")]
+    fn builtin_is_attrs(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        let value = x.force(vm)?;
+        Ok(Value::Bool(matches!(*value, Value::Attrs(_))))
+    }
+
+    #[builtin("isBool")]
+    fn builtin_is_bool(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        let value = x.force(vm)?;
+        Ok(Value::Bool(matches!(*value, Value::Bool(_))))
+    }
+
+    #[builtin("isFloat")]
+    fn builtin_is_float(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        let value = x.force(vm)?;
+        Ok(Value::Bool(matches!(*value, Value::Float(_))))
+    }
+
+    #[builtin("isFunction")]
+    fn builtin_is_function(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        let value = x.force(vm)?;
+        Ok(Value::Bool(matches!(
+            *value,
+            Value::Closure(_) | Value::Builtin(_)
+        )))
+    }
+
+    #[builtin("isInt")]
+    fn builtin_is_int(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        let value = x.force(vm)?;
+        Ok(Value::Bool(matches!(*value, Value::Integer(_))))
+    }
+
+    #[builtin("isList")]
+    fn builtin_is_list(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        let value = x.force(vm)?;
+        Ok(Value::Bool(matches!(*value, Value::List(_))))
+    }
+
+    #[builtin("isNull")]
+    fn builtin_is_null(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        let value = x.force(vm)?;
+        Ok(Value::Bool(matches!(*value, Value::Null)))
+    }
+
+    #[builtin("isPath")]
+    fn builtin_is_path(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        let value = x.force(vm)?;
+        Ok(Value::Bool(matches!(*value, Value::Path(_))))
+    }
+
+    #[builtin("isString")]
+    fn builtin_is_string(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        let value = x.force(vm)?;
+        Ok(Value::Bool(matches!(*value, Value::String(_))))
+    }
+
+    #[builtin("length")]
+    fn builtin_length(_: &mut VM, list: Value) -> Result<Value, ErrorKind> {
+        Ok(Value::Integer(list.to_list()?.len() as i64))
+    }
+
+    #[builtin("lessThan")]
+    fn builtin_less_than(
+        vm: &mut VM,
+        #[lazy] x: Value,
+        #[lazy] y: Value,
+    ) -> Result<Value, ErrorKind> {
+        Ok(Value::Bool(matches!(
+            x.force(vm)?.nix_cmp(&*y.force(vm)?, vm)?,
+            Some(Ordering::Less)
+        )))
+    }
+
+    #[builtin("listToAttrs")]
+    fn builtin_list_to_attrs(vm: &mut VM, list: Value) -> Result<Value, ErrorKind> {
+        let list = list.to_list()?;
+        let mut map = BTreeMap::new();
+        for val in list {
+            let attrs = val.force(vm)?.to_attrs()?;
+            let get = |key| {
+                attrs
+                    .select(key)
+                    .ok_or(ErrorKind::AttributeNotFound { name: key.into() })
+            };
+            let name = get("name")?.to_str()?;
+            let value = get("value")?.clone();
+            // Map entries earlier in the list take precedence over entries later in the list
+            map.entry(name).or_insert(value);
+        }
+        Ok(Value::attrs(NixAttrs::from_map(map)))
+    }
+
+    #[builtin("map")]
+    fn builtin_map(vm: &mut VM, f: Value, list: Value) -> Result<Value, ErrorKind> {
+        let list: NixList = list.to_list()?;
+
+        list.into_iter()
+            .map(|val| vm.call_with(&f, [val]))
+            .collect::<Result<Vec<Value>, _>>()
+            .map(|list| Value::List(NixList::from(list)))
+            .map_err(Into::into)
+    }
+
+    #[builtin("mapAttrs")]
+    fn builtin_map_attrs(vm: &mut VM, f: Value, attrs: Value) -> Result<Value, ErrorKind> {
+        let attrs = attrs.to_attrs()?;
+        let mut res = BTreeMap::new();
+        for (key, value) in attrs.as_ref() {
+            let value = vm.call_with(&f, [key.clone().into(), value.clone()])?;
+            res.insert(key.clone(), value);
+        }
+        Ok(Value::attrs(NixAttrs::from_map(res)))
+    }
+
+    #[builtin("match")]
+    fn builtin_match(_: &mut VM, regex: Value, str: Value) -> Result<Value, ErrorKind> {
+        let s = str.to_str()?;
+        let re = regex.to_str()?;
+        let re: Regex = Regex::new(&format!("^{}$", re.as_str())).unwrap();
+        match re.captures(&s) {
+            Some(caps) => Ok(caps
+                .iter()
+                .skip(1)
+                .map(|grp| grp.map(|g| Value::from(g.as_str())).unwrap_or(Value::Null))
+                .collect::<Vec<Value>>()
+                .into()),
+            None => Ok(Value::Null),
+        }
+    }
+
+    #[builtin("mul")]
+    fn builtin_mul(vm: &mut VM, #[lazy] x: Value, #[lazy] y: Value) -> Result<Value, ErrorKind> {
+        arithmetic_op!(&*x.force(vm)?, &*y.force(vm)?, *)
+    }
+
+    #[builtin("parseDrvName")]
+    fn builtin_parse_drv_name(_vm: &mut VM, s: Value) -> Result<Value, ErrorKind> {
+        // This replicates cppnix's (mis?)handling of codepoints
+        // above U+007f following 0x2d ('-')
+        let s = s.to_str()?;
+        let slice: &[u8] = s.as_str().as_ref();
+        let (name, dash_and_version) = slice.split_at(
+            slice
+                .windows(2)
+                .enumerate()
+                .find_map(|x| match x {
+                    (idx, [b'-', c1]) if !c1.is_ascii_alphabetic() => Some(idx),
+                    _ => None,
                 })
-                .collect::<Result<Vec<Value>, _>>()
-                .map(|list| Value::List(NixList::from(list)))
-                .map_err(Into::into)
-        }),
-        Builtin::new("floor", &[true], |args: Vec<Value>, _: &mut VM| {
-            Ok(Value::Integer(args[0].as_float()?.floor() as i64))
-        }),
-        Builtin::new(
-            "foldl'",
-            &[true, false, true],
-            |mut args: Vec<Value>, vm: &mut VM| {
-                let list = args.pop().unwrap().to_list()?;
-                let mut res = args.pop().unwrap();
-                let op = args.pop().unwrap();
-                for val in list {
-                    res = vm.call_with(&op, [res, val])?;
-                    res.force(vm)?;
-                }
+                .unwrap_or(slice.len()),
+        );
+        let version = dash_and_version
+            .split_first()
+            .map(|x| core::str::from_utf8(x.1))
+            .unwrap_or(Ok(""))?
+            .into();
+        Ok(Value::attrs(NixAttrs::from_map(BTreeMap::from([
+            (NixString::NAME, core::str::from_utf8(name)?.into()),
+            ("version".into(), version),
+        ]))))
+    }
+    #[builtin("partition")]
+    fn builtin_partition(vm: &mut VM, pred: Value, list: Value) -> Result<Value, ErrorKind> {
+        let mut right: Vec<Value> = vec![];
+        let mut wrong: Vec<Value> = vec![];
 
-                Ok(res)
-            },
-        ),
-        Builtin::new("functionArgs", &[true], |args: Vec<Value>, _: &mut VM| {
-            let lambda = args[0].to_closure()?.lambda();
-            let formals = if let Some(formals) = &lambda.formals {
-                formals
+        let list: NixList = list.to_list()?;
+        for elem in list.into_iter() {
+            let result = vm.call_with(&pred, [elem.clone()])?;
+
+            if result.force(vm)?.as_bool()? {
+                right.push(elem);
             } else {
-                return Ok(Value::attrs(NixAttrs::empty()));
+                wrong.push(elem);
             };
-            Ok(Value::attrs(NixAttrs::from_map(
-                formals
-                    .arguments
-                    .iter()
-                    .map(|(k, v)| (k.clone(), (*v).into()))
-                    .collect(),
-            )))
-        }),
-        Builtin::new("fromJSON", &[true], |args: Vec<Value>, _: &mut VM| {
-            let json_str = args[0].to_str()?;
-            let json: serde_json::Value = serde_json::from_str(&json_str)?;
-            json.try_into()
-        }),
-        Builtin::new("genList", &[true, true], |args: Vec<Value>, vm: &mut VM| {
-            let len = args[1].as_int()?;
-            (0..len)
-                .map(|i| vm.call_with(&args[0], [i.into()]))
-                .collect::<Result<Vec<Value>, _>>()
-                .map(|list| Value::List(NixList::from(list)))
-                .map_err(Into::into)
-        }),
-        Builtin::new("getAttr", &[true, true], |args: Vec<Value>, _: &mut VM| {
-            let k = args[0].to_str()?;
-            let xs = args[1].to_attrs()?;
+        }
 
-            match xs.select(k.as_str()) {
-                Some(x) => Ok(x.clone()),
-                None => Err(ErrorKind::AttributeNotFound {
-                    name: k.to_string(),
-                }),
-            }
-        }),
-        Builtin::new("groupBy", &[true, true], |args: Vec<Value>, vm: &mut VM| {
-            let mut res: BTreeMap<NixString, Value> = BTreeMap::new();
-            for val in args[1].to_list()? {
-                let key = vm.call_with(&args[0], [val.clone()])?.force(vm)?.to_str()?;
-                res.entry(key)
-                    .or_insert_with(|| Value::List(NixList::new()))
-                    .as_list_mut()?
-                    .push(val);
-            }
-            Ok(Value::attrs(NixAttrs::from_map(res)))
-        }),
-        Builtin::new("hasAttr", &[true, true], |args: Vec<Value>, _: &mut VM| {
-            let k = args[0].to_str()?;
-            let xs = args[1].to_attrs()?;
+        let mut res: BTreeMap<NixString, Value> = BTreeMap::new();
+        res.insert("right".into(), Value::List(right.into()));
+        res.insert("wrong".into(), Value::List(wrong.into()));
 
-            Ok(Value::Bool(xs.contains(k.as_str())))
-        }),
-        Builtin::new("head", &[true], |args: Vec<Value>, _: &mut VM| {
-            match args[0].to_list()?.get(0) {
-                Some(x) => Ok(x.clone()),
-                None => Err(ErrorKind::IndexOutOfBounds { index: 0 }),
-            }
-        }),
-        Builtin::new(
-            "intersectAttrs",
-            &[true, true],
-            |args: Vec<Value>, _: &mut VM| {
-                let mut res = BTreeMap::new();
-                let attrs1 = args[0].to_attrs()?;
-                let attrs2 = args[1].to_attrs()?;
-                for (k, v) in attrs2.iter() {
-                    if attrs1.contains(k) {
-                        res.insert(k.clone(), v.clone());
-                    }
-                }
-                Ok(Value::attrs(NixAttrs::from_map(res)))
-            },
-        ),
-        // For `is*` predicates we force manually, as Value::force also unwraps any Thunks
-        Builtin::new("isAttrs", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let value = args[0].force(vm)?;
-            Ok(Value::Bool(matches!(*value, Value::Attrs(_))))
-        }),
-        Builtin::new("isBool", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let value = args[0].force(vm)?;
-            Ok(Value::Bool(matches!(*value, Value::Bool(_))))
-        }),
-        Builtin::new("isFloat", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let value = args[0].force(vm)?;
-            Ok(Value::Bool(matches!(*value, Value::Float(_))))
-        }),
-        Builtin::new("isFunction", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let value = args[0].force(vm)?;
-            Ok(Value::Bool(matches!(
-                *value,
-                Value::Closure(_) | Value::Builtin(_)
-            )))
-        }),
-        Builtin::new("isInt", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let value = args[0].force(vm)?;
-            Ok(Value::Bool(matches!(*value, Value::Integer(_))))
-        }),
-        Builtin::new("isList", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let value = args[0].force(vm)?;
-            Ok(Value::Bool(matches!(*value, Value::List(_))))
-        }),
-        Builtin::new("isNull", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let value = args[0].force(vm)?;
-            Ok(Value::Bool(matches!(*value, Value::Null)))
-        }),
-        Builtin::new("isPath", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let value = args[0].force(vm)?;
-            Ok(Value::Bool(matches!(*value, Value::Path(_))))
-        }),
-        Builtin::new("isString", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let value = args[0].force(vm)?;
-            Ok(Value::Bool(matches!(*value, Value::String(_))))
-        }),
-        Builtin::new("length", &[true], |args: Vec<Value>, _: &mut VM| {
-            Ok(Value::Integer(args[0].to_list()?.len() as i64))
-        }),
-        Builtin::new(
-            "lessThan",
-            &[false, false],
-            |args: Vec<Value>, vm: &mut VM| {
-                Ok(Value::Bool(matches!(
-                    args[0].force(vm)?.nix_cmp(&*args[1].force(vm)?, vm)?,
-                    Some(Ordering::Less)
-                )))
-            },
-        ),
-        Builtin::new("listToAttrs", &[true], |args: Vec<Value>, vm: &mut VM| {
-            let list = args[0].to_list()?;
-            let mut map = BTreeMap::new();
-            for val in list {
-                let attrs = val.force(vm)?.to_attrs()?;
-                let get = |key| {
-                    attrs
-                        .select(key)
-                        .ok_or(ErrorKind::AttributeNotFound { name: key.into() })
-                };
-                let name = get("name")?.to_str()?;
-                let value = get("value")?.clone();
-                // Map entries earlier in the list take precedence over entries later in the list
-                map.entry(name).or_insert(value);
-            }
-            Ok(Value::attrs(NixAttrs::from_map(map)))
-        }),
-        Builtin::new("map", &[true, true], |args: Vec<Value>, vm: &mut VM| {
-            let list: NixList = args[1].to_list()?;
-
-            list.into_iter()
-                .map(|val| vm.call_with(&args[0], [val]))
-                .collect::<Result<Vec<Value>, _>>()
-                .map(|list| Value::List(NixList::from(list)))
-                .map_err(Into::into)
-        }),
-        Builtin::new(
-            "mapAttrs",
-            &[true, true],
-            |args: Vec<Value>, vm: &mut VM| {
-                let attrs = args[1].to_attrs()?;
-                let mut res = BTreeMap::new();
-                for (key, value) in attrs.as_ref() {
-                    let value = vm.call_with(&args[0], [key.clone().into(), value.clone()])?;
-                    res.insert(key.clone(), value);
-                }
-                Ok(Value::attrs(NixAttrs::from_map(res)))
-            },
-        ),
-        Builtin::new(
-            "match",
-            &[true, true],
-            |mut args: Vec<Value>, _: &mut VM| {
-                let s = args.pop().unwrap().to_str()?;
-                let re = args.pop().unwrap().to_str()?;
-                let re: Regex = Regex::new(&format!("^{}$", re.as_str())).unwrap();
-                match re.captures(&s) {
-                    Some(caps) => Ok(caps
-                        .iter()
-                        .skip(1)
-                        .map(|grp| grp.map(|g| Value::from(g.as_str())).unwrap_or(Value::Null))
-                        .collect::<Vec<Value>>()
-                        .into()),
-                    None => Ok(Value::Null),
-                }
-            },
-        ),
-        Builtin::new(
-            "mul",
-            &[false, false],
-            |args: Vec<Value>, vm: &mut VM| arithmetic_op!(&*args[0].force(vm)?, &*args[1].force(vm)?, *),
-        ),
-        Builtin::new("parseDrvName", &[true], |args: Vec<Value>, _vm: &mut VM| {
-            // This replicates cppnix's (mis?)handling of codepoints
-            // above U+007f following 0x2d ('-')
-            let s = args[0].to_str()?;
-            let slice: &[u8] = s.as_str().as_ref();
-            let (name, dash_and_version) = slice.split_at(
-                slice
-                    .windows(2)
-                    .enumerate()
-                    .find_map(|x| match x {
-                        (idx, [b'-', c1]) if !c1.is_ascii_alphabetic() => Some(idx),
-                        _ => None,
-                    })
-                    .unwrap_or(slice.len()),
-            );
-            let version = dash_and_version
-                .split_first()
-                .map(|x| core::str::from_utf8(x.1))
-                .unwrap_or(Ok(""))?
-                .into();
-            Ok(Value::attrs(NixAttrs::from_map(BTreeMap::from([
-                (NixString::NAME, core::str::from_utf8(name)?.into()),
-                ("version".into(), version),
-            ]))))
-        }),
-        Builtin::new(
-            "partition",
-            &[true, true],
-            |args: Vec<Value>, vm: &mut VM| {
-                let mut right: Vec<Value> = vec![];
-                let mut wrong: Vec<Value> = vec![];
-
-                let list: NixList = args[1].to_list()?;
-                for elem in list.into_iter() {
-                    let result = vm.call_with(&args[0], [elem.clone()])?;
-
-                    if result.force(vm)?.as_bool()? {
-                        right.push(elem);
-                    } else {
-                        wrong.push(elem);
-                    };
-                }
+        Ok(Value::attrs(NixAttrs::from_map(res)))
+    }
 
-                let mut res: BTreeMap<NixString, Value> = BTreeMap::new();
-                res.insert("right".into(), Value::List(right.into()));
-                res.insert("wrong".into(), Value::List(wrong.into()));
+    #[builtin("removeAttrs")]
+    fn builtin_remove_attrs(_: &mut VM, attrs: Value, keys: Value) -> Result<Value, ErrorKind> {
+        let attrs = attrs.to_attrs()?;
+        let keys = keys
+            .to_list()?
+            .into_iter()
+            .map(|v| v.to_str())
+            .collect::<Result<HashSet<_>, _>>()?;
+        let mut res = BTreeMap::new();
+        for (k, v) in attrs.iter() {
+            if !keys.contains(k) {
+                res.insert(k.clone(), v.clone());
+            }
+        }
+        Ok(Value::attrs(NixAttrs::from_map(res)))
+    }
 
-                Ok(Value::attrs(NixAttrs::from_map(res)))
-            },
-        ),
-        Builtin::new(
-            "removeAttrs",
-            &[true, true],
-            |args: Vec<Value>, _: &mut VM| {
-                let attrs = args[0].to_attrs()?;
-                let keys = args[1]
-                    .to_list()?
-                    .into_iter()
-                    .map(|v| v.to_str())
-                    .collect::<Result<HashSet<_>, _>>()?;
-                let mut res = BTreeMap::new();
-                for (k, v) in attrs.iter() {
-                    if !keys.contains(k) {
-                        res.insert(k.clone(), v.clone());
-                    }
+    #[builtin("replaceStrings")]
+    fn builtin_replace_strings(
+        vm: &mut VM,
+        from: Value,
+        to: Value,
+        s: Value,
+    ) -> Result<Value, ErrorKind> {
+        let from = from.to_list()?;
+        from.force_elements(vm)?;
+        let to = to.to_list()?;
+        to.force_elements(vm)?;
+        let string = s.to_str()?;
+
+        let mut res = String::new();
+
+        let mut i: usize = 0;
+        let mut empty_string_replace = false;
+
+        // This can't be implemented using Rust's string.replace() as
+        // well as a map because we need to handle errors with results
+        // as well as "reset" the iterator to zero for the replacement
+        // everytime there's a successful match.
+        // Also, Rust's string.replace allocates a new string
+        // on every call which is not preferable.
+        'outer: while i < string.len() {
+            // Try a match in all the from strings
+            for elem in std::iter::zip(from.iter(), to.iter()) {
+                let from = elem.0.to_str()?;
+                let to = elem.1.to_str()?;
+
+                if i + from.len() >= string.len() {
+                    continue;
                 }
-                Ok(Value::attrs(NixAttrs::from_map(res)))
-            },
-        ),
-        Builtin::new(
-            "replaceStrings",
-            &[true, true, true],
-            |args: Vec<Value>, vm: &mut VM| {
-                let from = args[0].to_list()?;
-                from.force_elements(vm)?;
-                let to = args[1].to_list()?;
-                to.force_elements(vm)?;
-                let string = args[2].to_str()?;
-
-                let mut res = String::new();
-
-                let mut i: usize = 0;
-                let mut empty_string_replace = false;
-
-                // This can't be implemented using Rust's string.replace() as
-                // well as a map because we need to handle errors with results
-                // as well as "reset" the iterator to zero for the replacement
-                // everytime there's a successful match.
-                // Also, Rust's string.replace allocates a new string
-                // on every call which is not preferable.
-                'outer: while i < string.len() {
-                    // Try a match in all the from strings
-                    for elem in std::iter::zip(from.iter(), to.iter()) {
-                        let from = elem.0.to_str()?;
-                        let to = elem.1.to_str()?;
-
-                        if i + from.len() >= string.len() {
-                            continue;
-                        }
-
-                        // We already applied a from->to with an empty from
-                        // transformation.
-                        // Let's skip it so that we don't loop infinitely
-                        if empty_string_replace && from.as_str().len() == 0 {
-                            continue;
-                        }
-
-                        // if we match the `from` string, let's replace
-                        if &string[i..i + from.len()] == from.as_str() {
-                            res += &to;
-                            i += from.len();
-
-                            // remember if we applied the empty from->to
-                            empty_string_replace = from.as_str().len() == 0;
-
-                            continue 'outer;
-                        }
-                    }
-
-                    // If we don't match any `from`, we simply add a character
-                    res += &string[i..i + 1];
-                    i += 1;
-
-                    // Since we didn't apply anything transformation,
-                    // we reset the empty string replacement
-                    empty_string_replace = false;
+
+                // We already applied a from->to with an empty from
+                // transformation.
+                // Let's skip it so that we don't loop infinitely
+                if empty_string_replace && from.as_str().len() == 0 {
+                    continue;
                 }
 
-                // Special case when the string is empty or at the string's end
-                // and one of the from is also empty
-                for elem in std::iter::zip(from.iter(), to.iter()) {
-                    let from = elem.0.to_str()?;
-                    let to = elem.1.to_str()?;
+                // if we match the `from` string, let's replace
+                if &string[i..i + from.len()] == from.as_str() {
+                    res += &to;
+                    i += from.len();
 
-                    if from.as_str().len() == 0 {
-                        res += &to;
-                        break;
-                    }
-                }
-                Ok(Value::String(res.into()))
-            },
-        ),
-        Builtin::new("seq", &[true, true], |mut args: Vec<Value>, _: &mut VM| {
-            // The builtin calling infra has already forced both args for us, so
-            // we just return the second and ignore the first
-            Ok(args.pop().unwrap())
-        }),
-        Builtin::new(
-            "split",
-            &[true, true],
-            |mut args: Vec<Value>, _: &mut VM| {
-                let s = args.pop().unwrap().to_str()?;
-                let text = s.as_str();
-                let re = args.pop().unwrap().to_str()?;
-                let re: Regex = Regex::new(re.as_str()).unwrap();
-                let mut capture_locations = re.capture_locations();
-                let num_captures = capture_locations.len();
-                let mut ret = NixList::new();
-                let mut pos = 0;
-
-                while let Some(thematch) = re.captures_read_at(&mut capture_locations, text, pos) {
-                    // push the unmatched characters preceding the match
-                    ret.push(Value::from(&text[pos..thematch.start()]));
-
-                    // Push a list with one element for each capture
-                    // group in the regex, containing the characters
-                    // matched by that capture group, or null if no match.
-                    // We skip capture 0; it represents the whole match.
-                    let v: Vec<Value> = (1..num_captures)
-                        .map(|i| capture_locations.get(i))
-                        .map(|o| {
-                            o.map(|(start, end)| Value::from(&text[start..end]))
-                                .unwrap_or(Value::Null)
-                        })
-                        .collect();
-                    ret.push(Value::List(NixList::from(v)));
-                    pos = thematch.end();
+                    // remember if we applied the empty from->to
+                    empty_string_replace = from.as_str().len() == 0;
+
+                    continue 'outer;
                 }
+            }
 
-                // push the unmatched characters following the last match
-                ret.push(Value::from(&text[pos..]));
+            // If we don't match any `from`, we simply add a character
+            res += &string[i..i + 1];
+            i += 1;
 
-                Ok(Value::List(ret))
-            },
-        ),
-        Builtin::new("sort", &[true, true], |args: Vec<Value>, vm: &mut VM| {
-            let mut list = args[1].to_list()?;
-            let comparator = &args[0];
-
-            // Used to let errors "escape" from the sorting closure. If anything
-            // ends up setting an error, it is returned from this function.
-            let mut error: Option<ErrorKind> = None;
-
-            list.sort_by(|lhs, rhs| {
-                let result = vm
-                    .call_with(comparator, [lhs.clone(), rhs.clone()])
-                    .map_err(|err| ErrorKind::ThunkForce(Box::new(err)))
-                    .and_then(|v| v.force(vm)?.as_bool());
-
-                match (&error, result) {
-                    // The contained closure only returns a "less
-                    // than?"-boolean, no way to yield "equal".
-                    (None, Ok(true)) => Ordering::Less,
-                    (None, Ok(false)) => Ordering::Greater,
-
-                    // Closest thing to short-circuiting out if an error was
-                    // thrown.
-                    (Some(_), _) => Ordering::Equal,
-
-                    // Propagate the error if one was encountered.
-                    (_, Err(e)) => {
-                        error = Some(e);
-                        Ordering::Equal
-                    }
-                }
-            });
+            // Since we didn't apply anything transformation,
+            // we reset the empty string replacement
+            empty_string_replace = false;
+        }
+
+        // Special case when the string is empty or at the string's end
+        // and one of the from is also empty
+        for elem in std::iter::zip(from.iter(), to.iter()) {
+            let from = elem.0.to_str()?;
+            let to = elem.1.to_str()?;
 
-            match error {
-                None => Ok(Value::List(list)),
-                Some(e) => Err(e),
+            if from.as_str().len() == 0 {
+                res += &to;
+                break;
             }
-        }),
-        Builtin::new("splitVersion", &[true], |args: Vec<Value>, _: &mut VM| {
-            let s = args[0].to_str()?;
-            let s = VersionPartsIter::new(s.as_str());
-
-            let parts = s
-                .map(|s| {
-                    Value::String(match s {
-                        VersionPart::Number(n) => n.into(),
-                        VersionPart::Word(w) => w.into(),
-                    })
+        }
+        Ok(Value::String(res.into()))
+    }
+
+    #[builtin("seq")]
+    fn builtin_seq(_: &mut VM, _x: Value, y: Value) -> Result<Value, ErrorKind> {
+        // The builtin calling infra has already forced both args for us, so
+        // we just return the second and ignore the first
+        Ok(y)
+    }
+
+    #[builtin("split")]
+    fn builtin_split(_: &mut VM, regex: Value, str: Value) -> Result<Value, ErrorKind> {
+        let s = str.to_str()?;
+        let text = s.as_str();
+        let re = regex.to_str()?;
+        let re: Regex = Regex::new(re.as_str()).unwrap();
+        let mut capture_locations = re.capture_locations();
+        let num_captures = capture_locations.len();
+        let mut ret = NixList::new();
+        let mut pos = 0;
+
+        while let Some(thematch) = re.captures_read_at(&mut capture_locations, text, pos) {
+            // push the unmatched characters preceding the match
+            ret.push(Value::from(&text[pos..thematch.start()]));
+
+            // Push a list with one element for each capture
+            // group in the regex, containing the characters
+            // matched by that capture group, or null if no match.
+            // We skip capture 0; it represents the whole match.
+            let v: Vec<Value> = (1..num_captures)
+                .map(|i| capture_locations.get(i))
+                .map(|o| {
+                    o.map(|(start, end)| Value::from(&text[start..end]))
+                        .unwrap_or(Value::Null)
                 })
-                .collect::<Vec<Value>>();
-            Ok(Value::List(NixList::construct(parts.len(), parts)))
-        }),
-        Builtin::new("stringLength", &[false], |args: Vec<Value>, vm: &mut VM| {
-            // also forces the value
-            let s = args[0].coerce_to_string(CoercionKind::Weak, vm)?;
-            Ok(Value::Integer(s.as_str().len() as i64))
-        }),
-        Builtin::new(
-            "sub",
-            &[false, false],
-            |args: Vec<Value>, vm: &mut VM| arithmetic_op!(&*args[0].force(vm)?, &*args[1].force(vm)?, -),
-        ),
-        Builtin::new(
-            "substring",
-            &[true, true, true],
-            |args: Vec<Value>, _: &mut VM| {
-                let beg = args[0].as_int()?;
-                let len = args[1].as_int()?;
-                let x = args[2].to_str()?;
-
-                if beg < 0 {
-                    return Err(ErrorKind::IndexOutOfBounds { index: beg });
-                }
-                let beg = beg as usize;
+                .collect();
+            ret.push(Value::List(NixList::from(v)));
+            pos = thematch.end();
+        }
 
-                // Nix doesn't assert that the length argument is
-                // non-negative when the starting index is GTE the
-                // string's length.
-                if beg >= x.as_str().len() {
-                    return Ok(Value::String("".into()));
-                }
+        // push the unmatched characters following the last match
+        ret.push(Value::from(&text[pos..]));
 
-                if len < 0 {
-                    return Err(ErrorKind::NegativeLength { length: len });
+        Ok(Value::List(ret))
+    }
+
+    #[builtin("sort")]
+    fn builtin_sort(vm: &mut VM, comparator: Value, list: Value) -> Result<Value, ErrorKind> {
+        let mut list = list.to_list()?;
+
+        // Used to let errors "escape" from the sorting closure. If anything
+        // ends up setting an error, it is returned from this function.
+        let mut error: Option<ErrorKind> = None;
+
+        list.sort_by(|lhs, rhs| {
+            let result = vm
+                .call_with(&comparator, [lhs.clone(), rhs.clone()])
+                .map_err(|err| ErrorKind::ThunkForce(Box::new(err)))
+                .and_then(|v| v.force(vm)?.as_bool());
+
+            match (&error, result) {
+                // The contained closure only returns a "less
+                // than?"-boolean, no way to yield "equal".
+                (None, Ok(true)) => Ordering::Less,
+                (None, Ok(false)) => Ordering::Greater,
+
+                // Closest thing to short-circuiting out if an error was
+                // thrown.
+                (Some(_), _) => Ordering::Equal,
+
+                // Propagate the error if one was encountered.
+                (_, Err(e)) => {
+                    error = Some(e);
+                    Ordering::Equal
                 }
+            }
+        });
 
-                let len = len as usize;
-                let end = cmp::min(beg + len, x.as_str().len());
+        match error {
+            None => Ok(Value::List(list)),
+            Some(e) => Err(e),
+        }
+    }
 
-                Ok(Value::String(
-                    x.as_str()[(beg as usize)..(end as usize)].into(),
-                ))
-            },
-        ),
-        Builtin::new("tail", &[true], |args: Vec<Value>, _: &mut VM| {
-            let xs = args[0].to_list()?;
+    #[builtin("splitVersion")]
+    fn builtin_split_version(_: &mut VM, s: Value) -> Result<Value, ErrorKind> {
+        let s = s.to_str()?;
+        let s = VersionPartsIter::new(s.as_str());
 
-            if xs.len() == 0 {
-                Err(ErrorKind::TailEmptyList)
-            } else {
-                let output = xs.into_iter().skip(1).collect::<Vec<_>>();
-                Ok(Value::List(NixList::construct(output.len(), output)))
-            }
-        }),
-        Builtin::new("throw", &[true], |args: Vec<Value>, _: &mut VM| {
-            Err(ErrorKind::Throw(args[0].to_str()?.to_string()))
-        }),
+        let parts = s
+            .map(|s| {
+                Value::String(match s {
+                    VersionPart::Number(n) => n.into(),
+                    VersionPart::Word(w) => w.into(),
+                })
+            })
+            .collect::<Vec<Value>>();
+        Ok(Value::List(NixList::construct(parts.len(), parts)))
+    }
+
+    #[builtin("stringLength")]
+    fn builtin_string_length(vm: &mut VM, #[lazy] s: Value) -> Result<Value, ErrorKind> {
+        // also forces the value
+        let s = s.coerce_to_string(CoercionKind::Weak, vm)?;
+        Ok(Value::Integer(s.as_str().len() as i64))
+    }
+
+    #[builtin("sub")]
+    fn builtin_sub(vm: &mut VM, #[lazy] x: Value, #[lazy] y: Value) -> Result<Value, ErrorKind> {
+        arithmetic_op!(&*x.force(vm)?, &*y.force(vm)?, -)
+    }
+
+    #[builtin("substring")]
+    fn builtin_substring(
+        _: &mut VM,
+        start: Value,
+        len: Value,
+        s: Value,
+    ) -> Result<Value, ErrorKind> {
+        let beg = start.as_int()?;
+        let len = len.as_int()?;
+        let x = s.to_str()?;
+
+        if beg < 0 {
+            return Err(ErrorKind::IndexOutOfBounds { index: beg });
+        }
+        let beg = beg as usize;
+
+        // Nix doesn't assert that the length argument is
+        // non-negative when the starting index is GTE the
+        // string's length.
+        if beg >= x.as_str().len() {
+            return Ok(Value::String("".into()));
+        }
+
+        if len < 0 {
+            return Err(ErrorKind::NegativeLength { length: len });
+        }
+
+        let len = len as usize;
+        let end = cmp::min(beg + len, x.as_str().len());
+
+        Ok(Value::String(
+            x.as_str()[(beg as usize)..(end as usize)].into(),
+        ))
+    }
+
+    #[builtin("tail")]
+    fn builtin_tail(_: &mut VM, list: Value) -> Result<Value, ErrorKind> {
+        let xs = list.to_list()?;
+
+        if xs.len() == 0 {
+            Err(ErrorKind::TailEmptyList)
+        } else {
+            let output = xs.into_iter().skip(1).collect::<Vec<_>>();
+            Ok(Value::List(NixList::construct(output.len(), output)))
+        }
+    }
+
+    #[builtin("throw")]
+    fn builtin_throw(_: &mut VM, message: Value) -> Result<Value, ErrorKind> {
+        Err(ErrorKind::Throw(message.to_str()?.to_string()))
+    }
+
+    #[builtin("toString")]
+    fn builtin_to_string(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
         // coerce_to_string forces for us
-        Builtin::new("toString", &[false], |args: Vec<Value>, vm: &mut VM| {
-            args[0]
-                .coerce_to_string(CoercionKind::Strong, vm)
-                .map(Value::String)
-        }),
-        Builtin::new(
-            "trace",
-            &[true, true],
-            |mut args: Vec<Value>, _: &mut VM| {
-                let value = args.pop().unwrap();
-                let trace_value = args.pop().unwrap();
-                // TODO(grfn): `trace` should be pluggable and capturable, probably via a method on
-                // the VM
-                println!("trace: {} :: {}", trace_value, trace_value.type_of());
-                Ok(value)
-            },
-        ),
-        Builtin::new("tryEval", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let mut res = BTreeMap::new();
-            match args[0].force(vm) {
-                Ok(value) => {
-                    res.insert("value".into(), (*value).clone());
-                    res.insert("success".into(), true.into());
-                }
-                Err(e) if e.is_catchable() => {
-                    res.insert("value".into(), false.into());
-                    res.insert("success".into(), false.into());
-                }
-                Err(e) => return Err(e),
+        x.coerce_to_string(CoercionKind::Strong, vm)
+            .map(Value::String)
+    }
+
+    #[builtin("trace")]
+    fn builtin_trace(_: &mut VM, message: Value, value: Value) -> Result<Value, ErrorKind> {
+        // TODO(grfn): `trace` should be pluggable and capturable, probably via a method on
+        // the VM
+        println!("trace: {} :: {}", message, message.type_of());
+        Ok(value)
+    }
+
+    #[builtin("toPath")]
+    fn builtin_to_path(vm: &mut VM, #[lazy] s: Value) -> Result<Value, ErrorKind> {
+        let path: Value = crate::value::canon_path(coerce_value_to_path(&s, vm)?).into();
+        Ok(path.coerce_to_string(CoercionKind::Weak, vm)?.into())
+    }
+
+    #[builtin("tryEval")]
+    fn builtin_try_eval(vm: &mut VM, #[lazy] e: Value) -> Result<Value, ErrorKind> {
+        let mut res = BTreeMap::new();
+        match e.force(vm) {
+            Ok(value) => {
+                res.insert("value".into(), (*value).clone());
+                res.insert("success".into(), true.into());
             }
-            Ok(Value::attrs(NixAttrs::from_map(res)))
-        }),
-        Builtin::new("toPath", &[false], |args: Vec<Value>, vm: &mut VM| {
-            let path: Value = crate::value::canon_path(coerce_value_to_path(&args[0], vm)?).into();
-            Ok(path.coerce_to_string(CoercionKind::Weak, vm)?.into())
-        }),
-        Builtin::new("typeOf", &[false], |args: Vec<Value>, vm: &mut VM| {
-            // We force manually here because it also unwraps the Thunk
-            // representation, if any.
-            // TODO(sterni): it'd be nice if we didn't have to worry about this
-            let value = args[0].force(vm)?;
-            Ok(Value::String(value.type_of().into()))
-        }),
-    ];
+            Err(e) if e.is_catchable() => {
+                res.insert("value".into(), false.into());
+                res.insert("success".into(), false.into());
+            }
+            Err(e) => return Err(e),
+        }
+        Ok(Value::attrs(NixAttrs::from_map(res)))
+    }
 
-    bs.extend(pure_builtins::builtins());
-    bs
+    #[builtin("typeOf")]
+    fn builtin_type_of(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
+        // We force manually here because it also unwraps the Thunk
+        // representation, if any.
+        // TODO(sterni): it'd be nice if we didn't have to worry about this
+        let value = x.force(vm)?;
+        Ok(Value::String(value.type_of().into()))
+    }
 }
 
+pub use pure_builtins::builtins as pure_builtins;
+
 /// Placeholder builtins that technically have a function which we do
 /// not yet implement, but which is also not easily observable from
 /// within a pure evaluation context.