add a comment about the trait aliases

1 files changed, 2 insertions, 0 deletions

diff --git a/src/fexpr/mod.rs b/src/fexpr/mod.rs
index f765acf..5d12051 100644
--- a/src/fexpr/mod.rs
+++ b/src/fexpr/mod.rs
@@ -11,6 +11,8 @@ use itertools::Itertools;
 use lalrpop_util::{lalrpop_mod, lexer::Token, ParseError};
 use thiserror::Error;
 
+// Lalrpop chokes on the associated type specification (it doesn't expect the =), so we need to
+// define those aliases here in Rust and then import and use them in the grammar.
 trait DateProducer = filters::values::Producer<Output = chrono::DateTime<chrono::Utc>>;
 trait DurationProducer = filters::values::Producer<Output = chrono::Duration>;
 trait CountProducer = filters::values::Producer<Output = u8>;