condtional multi-unwrap and guard clauses

compiler/hir/hir.odin

@@ -134,6 +134,11 @@ Local :: struct {
 	parameter: bool,
 }
 
+Conditional_Unwrap :: struct {
+	expr:  Expr_Id,
+	local: Local_Id,
+}
+
 Stmt_Kind :: enum u8 {
 	Declaration,
 	Assignment,
@@ -155,13 +160,17 @@ Stmt :: struct {
 	expr:       Expr_Id,
 	iterator_type: types.Type,
 	pointer_capture: bool,
-	// `If` statements use `expr` as the condition and `then_body`/`else_body` as
-	// the branch statement lists.
+	// Boolean `If` statements use `expr` as the condition. Conditional unwraps
+	// use `unwraps` for the ordered optional expressions and capture locals, and
+	// `guard` for the optional boolean checked after every unwrap succeeds.
+	// Both forms use `then_body`/`else_body` as the branch statement lists.
 	// `While` statements use `expr` as the condition, `then_body` as the loop
 	// body, and `update` as the optional post-iteration statement.
 	// `For` statements use `expr` as the iterable, `local` as the item capture,
 	// `index_local` as the optional sequence index, and `iterator_type` as the
 	// normalized many-item pointer type for sequence iteration.
+	unwraps:    []Conditional_Unwrap,
+	guard:      Expr_Id,
 	then_body:  []Stmt_Id,
 	else_body:  []Stmt_Id,
 	update:     Stmt_Id,
@@ -232,6 +241,7 @@ destroy_module :: proc(module: ^Module) {
 		delete(expr.args, module.allocator)
 	}
 	for statement in module.statements {
+		delete(statement.unwraps, module.allocator)
 		delete(statement.then_body, module.allocator)
 		delete(statement.else_body, module.allocator)
 	}