Add skeleton code structure

Scaffold the basic modules for the program, and clean up unnecessary zig-init
template code. Pretty sketchy, but it's late and I don't have much time tonight
so it will have to do.

build.zig

···
 const std = @import("std");
 
-// Although this function looks imperative, it does not perform the build
-// directly and instead it mutates the build graph (`b`) that will be then
-// executed by an external runner. The functions in `std.Build` implement a DSL
-// for defining build steps and express dependencies between them, allowing the
-// build runner to parallelize the build automatically (and the cache system to
-// know when a step doesn't need to be re-run).
 pub fn build(b: *std.Build) void {
-    // Standard target options allow the person running `zig build` to choose
-    // what target to build for. Here we do not override the defaults, which
-    // means any target is allowed, and the default is native. Other options
-    // for restricting supported target set are available.
     const target = b.standardTargetOptions(.{});
-    // Standard optimization options allow the person running `zig build` to select
-    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
-    // set a preferred release mode, allowing the user to decide how to optimize.
     const optimize = b.standardOptimizeOption(.{});
-    // It's also possible to define more custom flags to toggle optional features
-    // of this build script using `b.option()`. All defined flags (including
-    // target and optimize options) will be listed when running `zig build --help`
-    // in this directory.
 
-    // This creates a module, which represents a collection of source files alongside
-    // some compilation options, such as optimization mode and linked system libraries.
-    // Zig modules are the preferred way of making Zig code available to consumers.
-    // addModule defines a module that we intend to make available for importing
-    // to our consumers. We must give it a name because a Zig package can expose
-    // multiple modules and consumers will need to be able to specify which
-    // module they want to access.
     const mod = b.addModule("rat_lisp", .{
-        // The root source file is the "entry point" of this module. Users of
-        // this module will only be able to access public declarations contained
-        // in this file, which means that if you have declarations that you
-        // intend to expose to consumers that were defined in other files part
-        // of this module, you will have to make sure to re-export them from
-        // the root file.
         .root_source_file = b.path("src/root.zig"),
-        // Later on we'll use this module as the root module of a test executable
-        // which requires us to specify a target.
         .target = target,
     });
 
-    // Here we define an executable. An executable needs to have a root module
-    // which needs to expose a `main` function. While we could add a main function
-    // to the module defined above, it's sometimes preferable to split business
-    // logic and the CLI into two separate modules.
-    //
-    // If your goal is to create a Zig library for others to use, consider if
-    // it might benefit from also exposing a CLI tool. A parser library for a
-    // data serialization format could also bundle a CLI syntax checker, for example.
-    //
-    // If instead your goal is to create an executable, consider if users might
-    // be interested in also being able to embed the core functionality of your
-    // program in their own executable in order to avoid the overhead involved in
-    // subprocessing your CLI tool.
-    //
-    // If neither case applies to you, feel free to delete the declaration you
-    // don't need and to put everything under a single module.
     const exe = b.addExecutable(.{
         .name = "rat_lisp",
         .root_module = b.createModule(.{
-            // b.createModule defines a new module just like b.addModule but,
-            // unlike b.addModule, it does not expose the module to consumers of
-            // this package, which is why in this case we don't have to give it a name.
             .root_source_file = b.path("src/main.zig"),
-            // Target and optimization levels must be explicitly wired in when
-            // defining an executable or library (in the root module), and you
-            // can also hardcode a specific target for an executable or library
-            // definition if desireable (e.g. firmware for embedded devices).
             .target = target,
             .optimize = optimize,
-            // List of modules available for import in source files part of the
-            // root module.
             .imports = &.{
-                // Here "rat_lisp" is the name you will use in your source code to
-                // import this module (e.g. `@import("rat_lisp")`). The name is
-                // repeated because you are allowed to rename your imports, which
-                // can be extremely useful in case of collisions (which can happen
-                // importing modules from different packages).
                 .{ .name = "rat_lisp", .module = mod },
             },
         }),
     });
 
-    // This declares intent for the executable to be installed into the
-    // install prefix when running `zig build` (i.e. when executing the default
-    // step). By default the install prefix is `zig-out/` but can be overridden
-    // by passing `--prefix` or `-p`.
     b.installArtifact(exe);
 
-    // This creates a top level step. Top level steps have a name and can be
-    // invoked by name when running `zig build` (e.g. `zig build run`).
-    // This will evaluate the `run` step rather than the default step.
-    // For a top level step to actually do something, it must depend on other
-    // steps (e.g. a Run step, as we will see in a moment).
     const run_step = b.step("run", "Run the app");
 
-    // This creates a RunArtifact step in the build graph. A RunArtifact step
-    // invokes an executable compiled by Zig. Steps will only be executed by the
-    // runner if invoked directly by the user (in the case of top level steps)
-    // or if another step depends on it, so it's up to you to define when and
-    // how this Run step will be executed. In our case we want to run it when
-    // the user runs `zig build run`, so we create a dependency link.
     const run_cmd = b.addRunArtifact(exe);
     run_step.dependOn(&run_cmd.step);
 
-    // By making the run step depend on the default step, it will be run from the
-    // installation directory rather than directly from within the cache directory.
     run_cmd.step.dependOn(b.getInstallStep());
 
-    // This allows the user to pass arguments to the application in the build
-    // command itself, like this: `zig build run -- arg1 arg2 etc`
     if (b.args) |args| {
         run_cmd.addArgs(args);
     }
 
-    // Creates an executable that will run `test` blocks from the provided module.
-    // Here `mod` needs to define a target, which is why earlier we made sure to
-    // set the releative field.
     const mod_tests = b.addTest(.{
         .root_module = mod,
     });
 
-    // A run step that will run the test executable.
     const run_mod_tests = b.addRunArtifact(mod_tests);
 
-    // Creates an executable that will run `test` blocks from the executable's
-    // root module. Note that test executables only test one module at a time,
-    // hence why we have to create two separate ones.
     const exe_tests = b.addTest(.{
         .root_module = exe.root_module,
     });
 
-    // A run step that will run the second test executable.
     const run_exe_tests = b.addRunArtifact(exe_tests);
 
-    // A top level step for running all tests. dependOn can be called multiple
-    // times and since the two run steps do not depend on one another, this will
-    // make the two of them run in parallel.
     const test_step = b.step("test", "Run tests");
     test_step.dependOn(&run_mod_tests.step);
     test_step.dependOn(&run_exe_tests.step);
-
-    // Just like flags, top level steps are also listed in the `--help` menu.
-    //
-    // The Zig build system is entirely implemented in userland, which means
-    // that it cannot hook into private compiler APIs. All compilation work
-    // orchestrated by the build system will result in other Zig compiler
-    // subcommands being invoked with the right flags defined. You can observe
-    // these invocations when one fails (or you pass a flag to increase
-    // verbosity) to validate assumptions and diagnose problems.
-    //
-    // Lastly, the Zig build system is relatively simple and self-contained,
-    // and reading its source code will allow you to master it.
 }

build.zig.zon

···
 .{
-    // This is the default name used by packages depending on this one. For
-    // example, when a user runs `zig fetch --save <url>`, this field is used
-    // as the key in the `dependencies` table. Although the user can choose a
-    // different name, most users will stick with this provided value.
-    //
-    // It is redundant to include "zig" in this name because it is already
-    // within the Zig package namespace.
     .name = .rat_lisp,
-    // This is a [Semantic Version](https://semver.org/).
-    // In a future version of Zig it will be used for package deduplication.
     .version = "0.0.0",
-    // Together with name, this represents a globally unique package
-    // identifier. This field is generated by the Zig toolchain when the
-    // package is first created, and then *never changes*. This allows
-    // unambiguous detection of one package being an updated version of
-    // another.
-    //
-    // When forking a Zig project, this id should be regenerated (delete the
-    // field and run `zig build`) if the upstream project is still maintained.
-    // Otherwise, the fork is *hostile*, attempting to take control over the
-    // original project's identity. Thus it is recommended to leave the comment
-    // on the following line intact, so that it shows up in code reviews that
-    // modify the field.
     .fingerprint = 0xee87fa05ccae38f0, // Changing this has security and trust implications.
-    // Tracks the earliest Zig version that the package considers to be a
-    // supported use case.
     .minimum_zig_version = "0.15.2",
-    // This field is optional.
-    // Each dependency must either provide a `url` and `hash`, or a `path`.
-    // `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
-    // Once all dependencies are fetched, `zig build` no longer requires
-    // internet connectivity.
-    .dependencies = .{
-        // See `zig fetch --save <url>` for a command-line interface for adding dependencies.
-        //.example = .{
-        //    // When updating this field to a new URL, be sure to delete the corresponding
-        //    // `hash`, otherwise you are communicating that you expect to find the old hash at
-        //    // the new URL. If the contents of a URL change this will result in a hash mismatch
-        //    // which will prevent zig from using it.
-        //    .url = "https://example.com/foo.tar.gz",
-        //
-        //    // This is computed from the file contents of the directory of files that is
-        //    // obtained after fetching `url` and applying the inclusion rules given by
-        //    // `paths`.
-        //    //
-        //    // This field is the source of truth; packages do not come from a `url`; they
-        //    // come from a `hash`. `url` is just one of many possible mirrors for how to
-        //    // obtain a package matching this `hash`.
-        //    //
-        //    // Uses the [multihash](https://multiformats.io/multihash/) format.
-        //    .hash = "...",
-        //
-        //    // When this is provided, the package is found in a directory relative to the
-        //    // build root. In this case the package's hash is irrelevant and therefore not
-        //    // computed. This field and `url` are mutually exclusive.
-        //    .path = "foo",
-        //
-        //    // When this is set to `true`, a package is declared to be lazily
-        //    // fetched. This makes the dependency only get fetched if it is
-        //    // actually used.
-        //    .lazy = false,
-        //},
-    },
-    // Specifies the set of files and directories that are included in this package.
-    // Only files and directories listed here are included in the `hash` that
-    // is computed for this package. Only files listed here will remain on disk
-    // when using the zig package manager. As a rule of thumb, one should list
-    // files required for compilation plus any license(s).
-    // Paths are relative to the build root. Use the empty string (`""`) to refer to
-    // the build root itself.
-    // A directory listed here means that all files within, recursively, are included.
+    .dependencies = .{},
     .paths = .{
         "build.zig",
         "build.zig.zon",
         "src",
-        // For example...
-        //"LICENSE",
-        //"README.md",
     },
 }

src/eval.zig

···
+//! TODO: Tree-walking s-expr evaluator.
+const std = @import("std");

src/lex.zig

···
+//! TODO: Lexing functionality. Intentionally separate from parsing.
+const std = @import("std");
+
+// Unresolved questions: OOP stateful nonsense or can we just have A Function?
+
+/// TODO: Process a code string into a flat array of tokens.
+pub fn lex(allocator: std.mem.Allocator, code: []const u8) !std.ArrayList(Lexeme) {
+    _ = allocator;
+    _ = code;
+    return error.Todo;
+}
+
+pub const Lexeme = struct {
+    text: []const u8,
+    kind: Kind,
+
+    const Kind = enum {
+        l_paren,
+        r_paren,
+        identifier,
+        number,
+        string,
+        inert,
+        ignore,
+    };
+};

src/main.zig

···
 const std = @import("std");
-const rat_lisp = @import("rat_lisp");
+const rl = @import("rat_lisp");
 
 pub fn main() !void {
-    // Prints to stderr, ignoring potential errors.
-    std.debug.print("All your {s} are belong to us.\n", .{"codebase"});
-    try rat_lisp.bufferedPrint();
-}
-
-test "simple test" {
-    const gpa = std.testing.allocator;
-    var list: std.ArrayList(i32) = .empty;
-    defer list.deinit(gpa); // Try commenting this out and see if zig detects the memory leak!
-    try list.append(gpa, 42);
-    try std.testing.expectEqual(@as(i32, 42), list.pop());
-}
-
-test "fuzz example" {
-    const Context = struct {
-        fn testOne(context: @This(), input: []const u8) anyerror!void {
-            _ = context;
-            // Try passing `--fuzz` to `zig build test` and see if it manages to fail this test case!
-            try std.testing.expect(!std.mem.eql(u8, "canyoufindme", input));
-        }
-    };
-    try std.testing.fuzz(Context{}, Context.testOne, .{});
+    var gpa: std.heap.DebugAllocator(.{}) = .init;
+    const allocator = gpa.allocator();
+    // TODO: somehow turn this into a proper REPL
+    // TODO: the prompt for the repl should be `:>` ofc
+    const code = @embedFile("example.rats");
+    _ = try rl.read(allocator, code);
+    // TODO: eval
+    // TODO: print
+    // TODO: loop!
 }

src/parse.zig

···
+//! TODO: Parsing functionality. Intentionally separate from lexing.
+const std = @import("std");
+
+const lex = @import("lex.zig");
+
+pub fn parse(allocator: std.mem.Allocator, lexemes: std.ArrayList(lex.Lexeme)) !Ast {
+    _ = allocator;
+    _ = lexemes;
+    return error.Todo;
+}
+
+// TODO: AST
+// the AST will be a flat array(list?) of nodes, indexed by a handle type. nodes that contain other
+// nodes will merely contain these handles.
+
+pub const Ast = struct {
+    nodes: std.ArrayList(Node),
+
+    pub const Node = union(enum) {
+        pair: struct { car: Handle, cdr: Handle },
+        boolean: bool,
+        number: f64,
+        symbol: []const u8, // TODO: interning!
+        string: []const u8, // TODO: interning?
+        inert,
+        ignore,
+
+        pub const Handle = enum(u32) { _ };
+    };
+};

src/root.zig

···
-//! By convention, root.zig is the root source file when making a library.
+//! TODO: Root library module.
 const std = @import("std");
 
-pub fn bufferedPrint() !void {
-    // Stdout is for the actual output of your application, for example if you
-    // are implementing gzip, then only the compressed bytes should be sent to
-    // stdout, not any debugging messages.
-    var stdout_buffer: [1024]u8 = undefined;
-    var stdout_writer = std.fs.File.stdout().writer(&stdout_buffer);
-    const stdout = &stdout_writer.interface;
+const lex = @import("lex.zig");
+const parse = @import("parse.zig");
+const eval = @import("eval.zig");
 
-    try stdout.print("Run `zig build test` to run the tests.\n", .{});
+// TODO: io/reader function(s)
 
-    try stdout.flush(); // Don't forget to flush!
-}
-
-pub fn add(a: i32, b: i32) i32 {
-    return a + b;
-}
-
-test "basic add functionality" {
-    try std.testing.expect(add(3, 7) == 10);
+/// TODO: Lex and parse a string of source code and return the AST.
+pub fn read(allocator: std.mem.Allocator, code: []const u8) !parse.Ast {
+    const lexemes = try lex.lex(allocator, code);
+    return parse.parse(allocator, lexemes);
 }