Function interp_position 

fn interp_position(
    positional: &[RValue],
    named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Find the position (1-based index) of the first element where a predicate is TRUE.

@param f predicate function returning a logical scalar @param x vector or list to search @param right if TRUE, search from right to left @return scalar integer position, or NULL if none found