feat(tvix/eval): implement simple arithmetic binary operations r/4410

Implements simple arithmetic operations (+, -, *, /).

There is some scaffolding included to pop and coerce pairs of numbers,
as the Nix language will let arithmetic operators apply to arbitrary
pairs of number types (always resulting in floats if the types are
mixed).

Change-Id: I5f62c363bdea8baa6ef812cc64c5406759d257cf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6074
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

1 files changed, 25 insertions, 0 deletions

diff --git a/tvix/eval/src/value.rs b/tvix/eval/src/value.rs
index 037284b144..cbfff55b49 100644
--- a/tvix/eval/src/value.rs
+++ b/tvix/eval/src/value.rs
@@ -8,3 +8,28 @@ pub enum Value {
     Integer(i64),
     Float(f64),
 }
+
+impl Value {
+    pub fn is_number(&self) -> bool {
+        match self {
+            Value::Integer(_) => true,
+            Value::Float(_) => true,
+            _ => false,
+        }
+    }
+
+    pub fn type_of(&self) -> &'static str {
+        match self {
+            Value::Null => "null",
+            Value::Bool(_) => "bool",
+            Value::Integer(_) => "int",
+            Value::Float(_) => "float",
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum NumberPair {
+    Floats(f64, f64),
+    Integer(i64, i64),
+}