Function eval 

pub fn eval(
    expr: &Expr,
    invocation: &mut Invocation<'_>,
    memory: &mut Memory,
    program: &Program,
) -> Result<Value, Error>

Evaluate an expression through the single-pass frame evaluator.

Errors

Returns Error::Interp when expression lowering or flat execution fails. The recursive evaluator is retained only as a test oracle.