1 files changed, 112 insertions, 0 deletions
diff --git a/tvix/eval/src/value/function.rs b/tvix/eval/src/value/function.rs
new file mode 100644
index 0000000000..7592e3d641
--- /dev/null
+++ b/tvix/eval/src/value/function.rs
@@ -0,0 +1,112 @@
+//! This module implements the runtime representation of functions.
+use std::{collections::BTreeMap, hash::Hash, rc::Rc};
+
+use codemap::Span;
+use smol_str::SmolStr;
+
+use crate::{chunk::Chunk, upvalues::Upvalues};
+
+use super::NixString;
+
+#[derive(Clone, Debug, PartialEq)]
+pub(crate) struct Formals {
+    /// Map from argument name, to whether that argument is required
+    pub(crate) arguments: BTreeMap<NixString, bool>,
+
+    /// Do the formals of this function accept extra arguments
+    pub(crate) ellipsis: bool,
+
+    /// The span of the formals themselves, to use to emit errors
+    pub(crate) span: Span,
+
+    /// Optionally tracks a name for all function arguments (args@ style).
+    /// Used by toXML.
+    pub(crate) name: Option<String>,
+}
+
+impl Formals {
+    /// Returns true if the given arg is a valid argument to these formals.
+    ///
+    /// This is true if it is either listed in the list of arguments, or the formals have an
+    /// ellipsis
+    pub(crate) fn contains<Q>(&self, arg: &Q) -> bool
+    where
+        Q: ?Sized + Hash + Ord + Eq,
+        NixString: std::borrow::Borrow<Q>,
+    {
+        self.ellipsis || self.arguments.contains_key(arg)
+    }
+}
+
+/// The opcodes for a thunk or closure, plus the number of
+/// non-executable opcodes which are allowed after an OpThunkClosure or
+/// OpThunkSuspended referencing it.  At runtime `Lambda` is usually wrapped
+/// in `Rc` to avoid copying the `Chunk` it holds (which can be
+/// quite large).
+///
+/// In order to correctly reproduce cppnix's "pointer equality"
+/// semantics it is important that we never clone a Lambda --
+/// use `Rc<Lambda>::clone()` instead.  This struct deliberately
+/// does not `derive(Clone)` in order to prevent this from being
+/// done accidentally.
+///
+#[derive(/* do not add Clone here */ Debug, Default)]
+pub struct Lambda {
+    pub(crate) chunk: Chunk,
+
+    /// Name of the function (equivalent to the name of the
+    /// identifier (e.g. a value in a let-expression or an attribute
+    /// set entry) it is located in).
+    pub(crate) name: Option<SmolStr>,
+
+    /// Number of upvalues which the code in this Lambda closes
+    /// over, and which need to be initialised at
+    /// runtime.  Information about the variables is emitted using
+    /// data-carrying opcodes (see [`crate::opcode::OpCode::DataStackIdx`]).
+    pub(crate) upvalue_count: usize,
+    pub(crate) formals: Option<Formals>,
+}
+
+impl Lambda {
+    pub fn chunk(&mut self) -> &mut Chunk {
+        &mut self.chunk
+    }
+}
+
+///
+/// In order to correctly reproduce cppnix's "pointer equality"
+/// semantics it is important that we never clone a Lambda --
+/// use `Rc<Lambda>::clone()` instead.  This struct deliberately
+/// does not `derive(Clone)` in order to prevent this from being
+/// done accidentally.
+///
+#[derive(/* do not add Clone here */ Debug)]
+pub struct Closure {
+    pub lambda: Rc<Lambda>,
+    pub upvalues: Rc<Upvalues>,
+}
+
+impl Closure {
+    pub fn new(lambda: Rc<Lambda>) -> Self {
+        Self::new_with_upvalues(
+            Rc::new(Upvalues::with_capacity(lambda.upvalue_count)),
+            lambda,
+        )
+    }
+
+    pub fn new_with_upvalues(upvalues: Rc<Upvalues>, lambda: Rc<Lambda>) -> Self {
+        Closure { upvalues, lambda }
+    }
+
+    pub fn chunk(&self) -> &Chunk {
+        &self.lambda.chunk
+    }
+
+    pub fn lambda(&self) -> Rc<Lambda> {
+        self.lambda.clone()
+    }
+
+    pub fn upvalues(&self) -> Rc<Upvalues> {
+        self.upvalues.clone()
+    }
+}