Cleaning a Stack project

By default, if we have already compiled our project before (by using stack build, stack run or stack install), every use of stack build, stack run or stack install after that compiles only those files that have changed since the last time we compiled our project, and the files that depend on them. That's the same way make operates for C/C++ projects.

Sometimes, it is useful to ensure that all files are compiled from scratch, for example if we want to hunt down compiler warnings that we want to eliminate. To this end, we have the stack clean command. It deletes all files created by a previous run of the compiler. If we now run stack build, the project is built from scratch.

You have now learned everything you need to know to write Haskell code and to bundle it in a package you can build using Stack. Especially this section on packages was a bit dry though. Instead of working with our hello-world project and turning it into a slightly more meaningful toy project, we will spend the remaining three chapters of this book on implementing three complete projects that do something meaningful. We will implement a program that can find a path through a maze, we will implement the \(k\)-means clustering algorithm, and we will implement a parser for (phylogenetic) trees encoded in Newick format.