Move the Date struct into types and implement a get_property_numeric.

src/compare/util.rs

@@ -1,3 +1,5 @@
+use std::str::FromStr;
+
 use super::elisp_fact::GetElispFact;
 use super::sexp::Token;
 use crate::compare::sexp::unquote;
@@ -234,3 +236,23 @@ pub(crate) fn get_property_boolean<'b, 's, 'x>(
         .unwrap_or("nil")
         != "nil")
 }
+
+/// Get a named property containing an unquoted numeric value.
+///
+/// Returns None if key is not found.
+pub(crate) fn get_property_numeric<'b, 's, 'x, N: FromStr>(
+    emacs: &'b Token<'s>,
+    key: &'x str,
+) -> Result<Option<N>, Box<dyn std::error::Error>>
+where
+    <N as FromStr>::Err: std::error::Error,
+    <N as FromStr>::Err: 'static,
+{
+    let foo = get_property(emacs, key)?
+        .map(Token::as_atom)
+        .map_or(Ok(None), |r| r.map(Some))?;
+    let bar = foo
+        .map(|val| val.parse::<N>())
+        .map_or(Ok(None), |r| r.map(Some))?;
+    Ok(bar)
+}