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, 28 insertions, 3 deletions

diff --git a/tvix/eval/src/compiler.rs b/tvix/eval/src/compiler.rs
index 4a23db3dcb..65b97cd56c 100644
--- a/tvix/eval/src/compiler.rs
+++ b/tvix/eval/src/compiler.rs
@@ -6,17 +6,18 @@ use crate::errors::EvalResult;
 use crate::opcode::OpCode;
 use crate::value::Value;
 use rnix;
+use rnix::types::TypedNode;
 
 struct Compiler {
     chunk: Chunk,
 }
 
 impl Compiler {
-    fn compile(&mut self, node: &rnix::SyntaxNode) -> EvalResult<()> {
+    fn compile(&mut self, node: rnix::SyntaxNode) -> EvalResult<()> {
         match node.kind() {
             // Root of a file contains no content, it's just a marker
             // type.
-            rnix::SyntaxKind::NODE_ROOT => self.compile(&node.first_child().expect("TODO")),
+            rnix::SyntaxKind::NODE_ROOT => self.compile(node.first_child().expect("TODO")),
 
             // Literals contain a single token comprising of the
             // literal itself.
@@ -25,6 +26,11 @@ impl Compiler {
                 self.compile_literal(token)
             }
 
+            rnix::SyntaxKind::NODE_BIN_OP => {
+                let op = rnix::types::BinOp::cast(node).expect("TODO (should not be possible)");
+                self.compile_binop(op)
+            }
+
             kind => {
                 println!("visiting unsupported node: {:?}", kind);
                 Ok(())
@@ -52,6 +58,25 @@ impl Compiler {
             rnix::NixValue::Path(_, _) => todo!(),
         }
     }
+
+    fn compile_binop(&mut self, op: rnix::types::BinOp) -> EvalResult<()> {
+        self.compile(op.lhs().unwrap())?;
+        self.compile(op.rhs().unwrap())?;
+
+        use rnix::types::BinOpKind;
+
+        let opcode = match op.operator().unwrap() {
+            BinOpKind::Add => OpCode::OpAdd,
+            BinOpKind::Sub => OpCode::OpSub,
+            BinOpKind::Mul => OpCode::OpMul,
+            BinOpKind::Div => OpCode::OpDiv,
+
+            _ => todo!(),
+        };
+
+        self.chunk.add_op(opcode);
+        Ok(())
+    }
 }
 
 pub fn compile(ast: rnix::AST) -> EvalResult<Chunk> {
@@ -59,7 +84,7 @@ pub fn compile(ast: rnix::AST) -> EvalResult<Chunk> {
         chunk: Chunk::default(),
     };
 
-    c.compile(&ast.node())?;
+    c.compile(ast.node())?;
 
     Ok(c.chunk)
 }