Using A ref As A Mutable Global Flag

I have written a new, small Clojure program to compare this month’s and last month’s insurance report. This is similar to a project I did a year ago, except it involves one report our personnel department gets once a month, not two different reports. 

The program involves using Clojure’s jdbc interface, and is very much a typical database report that could have been written in Perl, or if the database had been Informix, in Informix 4GL. There’s nothing special about the program, except the code base was already in Clojure, and I wanted to keep the code base the same.

The only roadblock I ran into was setting status from the result of certain difference tests between last and this month, like whether a record wasn’t there this month, last month, whether or not the insurance product or premium had changed, or if someone had gone from an active to a retired status.

I tried figuring out a way to have a let binding contain return status from these different tests, so that these status values could be written into the report. After a while, I settled on a ref and dosync to set one global flag, so that later on in the program, had their been no errors, an appropriate message could be written to the file.

I don’t know whether I crossed into the mutable dark force, but, for one, I’m not convinced that carefully used mutable variables are a bad thing, especially, if you’ve designed the rest of your program not to take these shortcuts, because of coding laziness. Can you tell I’ve absorbed guilt from Clojure’s being immutable?


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