Add CMake file and code for post 4

content/blog/04_compiler_improvements.md

@@ -0,0 +1,68 @@
+---
+title: Compiling a Functional Language Using C++, Part 4 - Small Improvements
+date: 2019-08-06T14:26:38-07:00
+draft: true
+tags: ["C and C++", "Functional Languages", "Compilers"]
+---
+We've done quite a big push in the previous post. We defined
+type rules for our language, implemented unification,
+and then implemented unification to enforce these rules for
+our program. The post was pretty long, and even then we
+weren't able to fit quite everything into it.
+
+For instance, we threw 0 whenever an error occured. This
+gives us no indication of what actually went wrong. We should
+probably define an exception class, one that can contain
+information about the error, and report it to the user.
+
+Also, when there's no error, our compiler doesn't
+really tell us anything at all about the code besides
+the number of definitions. We probably want to see the types
+of these definitions, or at least some intermediate information.
+At the very least, we want to have the __ability__ to see
+this information.
+
+Finally, we have no build system. We are creating more
+and more source files, and so far (unless you've taken
+initiative), we've been compiling them by hand. We want
+to only compile source files that have changed,
+and we want to have a standard definition of how to
+build our program.
+
+### Setting up CMake
+This would be extremely easy if not for Flex and Bison. We start with the usual:
+{{< codelines "CMake" "compiler/04/CMakeLists.txt" 1 2 >}}
+
+Next, we want to set up Flex and Bison. CMake provides two commands for this:
+{{< codelines "CMake" "compiler/04/CMakeLists.txt" 4 5 >}}
+
+We now have access to commands that allow us to tell CMake about our parser
+and tokenizer (or scanner). We use them as follows:
+{{< codelines "CMake" "compiler/04/CMakeLists.txt" 6 12 >}}
+
+We also want CMake to know that the scanner needs to parser's header file
+in order to compile. We add this dependency:
+{{< codelines "CMake" "compiler/04/CMakeLists.txt" 13 13 >}}
+
+Finally, we add our source code to a CMake target. We use
+the `BISON_parser_OUTPUTS` and `FLEX_scanner_OUTPUTS` to
+pass in the source files generated by Flex and Bison.
+{{< codelines "CMake" "compiler/04/CMakeLists.txt" 15 22 >}}
+
+Almost there! `parser.cpp` will be generated in the `build` directory
+during an out-of-source build, and so will `parser.hpp`. When building,
+`parser.cpp` will try to look for `ast.hpp`, and `main.cpp` will look for
+`parser.hpp`. We want them to be able to find each other, so we
+add both the source directory and the build (binary) directory to
+the list of includes directories:
+
+{{< codelines "CMake" "compiler/04/CMakeLists.txt" 23 24 >}}
+
+That's it for CMake! Let's try our build:
+```
+cmake -S . -B build
+cd build && make -j8
+```
+
+We get an executable called `compiler`. Excellent! Here's the whole file:
+{{< codeblock "CMake" "compiler/04/CMakeLists.txt" >}}