feat(tvix/eval): implement unary negation operator r/4411

Change-Id: I5d012cc073e55d79d7b34b88283aab3164864293
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6075
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

3 files changed, 35 insertions, 1 deletions

diff --git a/tvix/eval/src/compiler.rs b/tvix/eval/src/compiler.rs
index 65b97cd56ccc..d71eda43aa36 100644
--- a/tvix/eval/src/compiler.rs
+++ b/tvix/eval/src/compiler.rs
@@ -31,6 +31,11 @@ impl Compiler {
                 self.compile_binop(op)
             }
 
+            rnix::SyntaxKind::NODE_UNARY_OP => {
+                let op = rnix::types::UnaryOp::cast(node).expect("TODO: (should not be possible)");
+                self.compile_unary_op(op)
+            }
+
             kind => {
                 println!("visiting unsupported node: {:?}", kind);
                 Ok(())
@@ -77,6 +82,19 @@ impl Compiler {
         self.chunk.add_op(opcode);
         Ok(())
     }
+
+    fn compile_unary_op(&mut self, op: rnix::types::UnaryOp) -> EvalResult<()> {
+        self.compile(op.value().unwrap())?;
+
+        use rnix::types::UnaryOpKind;
+        let opcode = match op.operator() {
+            UnaryOpKind::Invert => OpCode::OpInvert,
+            UnaryOpKind::Negate => OpCode::OpNegate,
+        };
+
+        self.chunk.add_op(opcode);
+        Ok(())
+    }
 }
 
 pub fn compile(ast: rnix::AST) -> EvalResult<Chunk> {
diff --git a/tvix/eval/src/opcode.rs b/tvix/eval/src/opcode.rs
index 307b695f6d9b..0aa252c4cc08 100644
--- a/tvix/eval/src/opcode.rs
+++ b/tvix/eval/src/opcode.rs
@@ -17,9 +17,13 @@ pub enum OpCode {
     OpTrue,
     OpFalse,
 
-    // Simple binary operators
+    // Arithmetic binary operators
     OpAdd,
     OpSub,
     OpMul,
     OpDiv,
+
+    // Unary operators
+    OpInvert,
+    OpNegate,
 }
diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index 077acfcc1b8d..da79867ef3f0 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -81,6 +81,18 @@ impl VM {
                     NumberPair::Integer(i1, i2) => self.push(Value::Integer(i1 / i2)),
                 },
 
+                OpCode::OpNegate => match self.pop() {
+                    Value::Integer(i) => self.push(Value::Integer(-i)),
+                    Value::Float(f) => self.push(Value::Float(-f)),
+                    v => {
+                        return Err(Error::TypeError {
+                            expected: "number (either int or float)",
+                            actual: v.type_of(),
+                        })
+                    }
+                },
+
+                OpCode::OpInvert => todo!(),
                 OpCode::OpNull => todo!(),
                 OpCode::OpTrue => todo!(),
                 OpCode::OpFalse => todo!(),