Add eval representation of DateSpec

src/eval/formula_spec.rs

@@ -1,6 +1,8 @@
-use crate::files::commands::{self, Expr, Time, Var};
+use crate::files::commands::{self, DoneDate, Expr, Time, Var};
+use crate::files::Source;
 
 use super::delta::{Delta, DeltaStep};
+use super::{Entry, Eval, Result};
 
 pub struct FormulaSpec {
     // TODO Implement more efficient exprs and expr evaluation
@@ -66,3 +68,13 @@ impl From<&commands::WeekdaySpec> for FormulaSpec {
         }
     }
 }
+
+impl Eval {
+    pub fn eval_formula_spec(
+        &mut self,
+        spec: FormulaSpec,
+        new_entry: impl Fn(Source, Option<DoneDate>) -> Entry,
+    ) -> Result<()> {
+        todo!()
+    }
+}