compound assignment

compiler/ast/ast.odin

@@ -84,6 +84,9 @@ Expr_Kind :: enum u8 {
 	Negate,
 	Not,
 	Add,
+	Sub,
+	Mul,
+	Div,
 	Eq,
 	Ne,
 	Lt,
@@ -126,6 +129,14 @@ Stmt_Kind :: enum u8 {
 	For,
 }
 
+Assignment_Op :: enum u8 {
+	Set,
+	Add,
+	Sub,
+	Mul,
+	Div,
+}
+
 Stmt :: struct {
 	kind:       Stmt_Kind,
 	span:       source.Span,
@@ -134,6 +145,10 @@ Stmt :: struct {
 	type:       Type_Syntax,
 	immutable:  bool,
 	pointer_capture: bool,
+	// Assignments store the lvalue in `target`, the right-hand side in `expr`,
+	// and the source operator in `assignment_op`. `Set` is ordinary `=`;
+	// the arithmetic variants are `+=`, `-=`, `*=`, and `/=`.
+	assignment_op: Assignment_Op,
 	target:     Expr_Id,
 	expr:       Expr_Id,
 	// `If` statements use `expr` as the condition, `captures` as optional