Concat previous field with a regular expression

In previous versions of Mockaroo I was able to concat a previous field value with a 9 digit regular expression - e.g. {{messageType}}\d{10} would generate something like 'AB47390846167’

This now generates {{messageType}}47390846167

Is there an equivalent way of doing this now without creating an extra field to hold the regular expression?

You can prepend the other field with an inline formula:

messageType + this

I’m not following. “this” is the \d{10} in the current field that I’m trying to append.
Maybe my question was not clear enough.
The field I originally had was defined as regex with \d{10} which correctly populated w/random 10-digit number.
Then, in same field, I added {{messageType}}\d{10} (leaving field as regex) and it correctly populated (concatenated) value of ‘messageType’ with the 10-digit number e.g. 'AB47390846167’
So ultimately, I’m asking how to concatenate the value from another field with current field of regex without creating a temporary field.