1 files changed, 2 insertions, 0 deletions
diff --git a/expr.h b/expr.h
index bfb372b6..a76d05f8 100644
--- a/expr.h
+++ b/expr.h
@@ -115,6 +115,8 @@ public:
   static value_t eval(const string& _expr, scope_t& scope);
 };
 
+std::ostream& operator<<(std::ostream& out, const expr_t& expr);
+
 } // namespace ledger
 
 #endif // _EXPR_H