pub fn expr_to_num(
expr_num: &Expr,
state: &mut EvaluationState,
traversal_state: &mut StateManager,
fns: &FunctionMap,
) -> Result<f64, Error>pub fn expr_to_num(
expr_num: &Expr,
state: &mut EvaluationState,
traversal_state: &mut StateManager,
fns: &FunctionMap,
) -> Result<f64, Error>