Function to_substrait_rex 

pub fn to_substrait_rex(
    producer: &mut impl SubstraitProducer,
    expr: &Expr,
    schema: &Arc<DFSchema>,
) -> Result<Expression, DataFusionError>

Convert DataFusion Expr to Substrait Rex

Arguments

• producer - SubstraitProducer implementation which the handles the actual conversion
• expr - DataFusion expression to convert into a Substrait expression
• schema - DataFusion input schema for looking up columns