Clojure Don’ts: Concat
Welcome to what I hope will be an ongoing series of Clojure do’s and don’ts. I want to demonstrate not just good patterns to use, but also anti-patterns to avoid.
Some of these will be personal preferences, others will be warnings from hard-won experience. I’ll try to indicate which is which.
concat is a tricky little function. The name suggests a way to combine two collections. And it is, if you have only two collections. But it’s not as general as you might think. It’s not really a collection function at all. It’s a lazy sequence function. The difference can be important.
Here’s an example that I see a lot in the wild. Say you have a loop that builds up some result collection as the concatenation of several intermediate results:1
So we have a stack overflow. But why? We used recur. Our code has no stack-consuming recursion. Or does it? (cue ominous music)
