From 7b85276fc98643b1138df6f322b8bd657339ea96 Mon Sep 17 00:00:00 2001
From: Mathias Magnusson <mathias@magnusson.space>
Date: Wed, 28 May 2025 23:00:32 +0200
Subject: initial commit

---
 .gitignore    |  2 ++
 build.zig     | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 build.zig.zon | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/lexer.zig | 66 +++++++++++++++++++++++++++++++++++++++++++++
 src/main.zig  | 46 ++++++++++++++++++++++++++++++++
 src/parse.zig | 50 ++++++++++++++++++++++++++++++++++
 src/peek.zig  | 51 +++++++++++++++++++++++++++++++++++
 7 files changed, 380 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 build.zig
 create mode 100644 build.zig.zon
 create mode 100644 src/lexer.zig
 create mode 100644 src/main.zig
 create mode 100644 src/parse.zig
 create mode 100644 src/peek.zig

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..db3cb54
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/.zig-cache/
+/zig-out/
diff --git a/build.zig b/build.zig
new file mode 100644
index 0000000..33e8492
--- /dev/null
+++ b/build.zig
@@ -0,0 +1,79 @@
+const std = @import("std");
+
+// Although this function looks imperative, note that its job is to
+// declaratively construct a build graph that will be executed by an external
+// runner.
+pub fn build(b: *std.Build) void {
+    // Standard target options allows 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(.{});
+
+    // We will also create a module for our other entry point, 'main.zig'.
+    const exe_mod = b.createModule(.{
+        // `root_source_file` is the Zig "entry point" of the module. If a module
+        // only contains e.g. external object files, you can make this `null`.
+        // In this case the main source file is merely a path, however, in more
+        // complicated build scripts, this could be a generated file.
+        .root_source_file = b.path("src/main.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+
+    // This creates another `std.Build.Step.Compile`, but this one builds an executable
+    // rather than a static library.
+    const exe = b.addExecutable(.{
+        .name = "huginn2",
+        .root_module = exe_mod,
+        .use_llvm = false,
+        .use_lld = false,
+    });
+
+    // This declares intent for the executable to be installed into the
+    // standard location when the user invokes the "install" step (the default
+    // step when running `zig build`).
+    b.installArtifact(exe);
+
+    // This *creates* a Run step in the build graph, to be executed when another
+    // step is evaluated that depends on it. The next line below will establish
+    // such a dependency.
+    const run_cmd = b.addRunArtifact(exe);
+
+    // By making the run step depend on the install step, it will be run from the
+    // installation directory rather than directly from within the cache directory.
+    // This is not necessary, however, if the application depends on other installed
+    // files, this ensures they will be present and in the expected location.
+    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);
+    }
+
+    // This creates a build step. It will be visible in the `zig build --help` menu,
+    // and can be selected like this: `zig build run`
+    // This will evaluate the `run` step rather than the default, which is "install".
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+
+    const exe_unit_tests = b.addTest(.{
+        .root_module = exe_mod,
+        .use_llvm = false,
+        .use_lld = false,
+    });
+
+    const run_exe_unit_tests = b.addRunArtifact(exe_unit_tests);
+
+    // Similar to creating the run step earlier, this exposes a `test` step to
+    // the `zig build --help` menu, providing a way for the user to request
+    // running the unit tests.
+    const test_step = b.step("test", "Run unit tests");
+    test_step.dependOn(&run_exe_unit_tests.step);
+}
diff --git a/build.zig.zon b/build.zig.zon
new file mode 100644
index 0000000..0ddded9
--- /dev/null
+++ b/build.zig.zon
@@ -0,0 +1,86 @@
+.{
+    // 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 = .huginn2,
+
+    // 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 = 0x6206a3d97ac08ad8, // 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 = "0.14.0",
+
+    // 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.
+    .paths = .{
+        "build.zig",
+        "build.zig.zon",
+        "src",
+        // For example...
+        //"LICENSE",
+        //"README.md",
+    },
+}
diff --git a/src/lexer.zig b/src/lexer.zig
new file mode 100644
index 0000000..93ed6cc
--- /dev/null
+++ b/src/lexer.zig
@@ -0,0 +1,66 @@
+pub const Token = struct {
+    start: usize,
+    end: usize,
+    type: Type,
+
+    pub const Type = union(enum) {
+        LeftParen,
+        RightParen,
+        IntegerLiteral: usize,
+        Plus,
+        Invalid,
+        Eof,
+    };
+};
+
+source: []const u8,
+last_end: usize = 0,
+pos: usize = 0,
+
+pub fn next(self: *Self) ?Token {
+    return s: switch (self.eat() orelse return self.create(.Eof)) {
+        '(' => self.create(.LeftParen),
+        ')' => self.create(.RightParen),
+        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' => |d| self.integerLiteral(d),
+        '+' => self.create(.Plus),
+        ' ' => {
+            self.last_end = self.pos;
+            continue :s (self.eat() orelse return self.create(.Eof));
+        },
+        else => self.create(.Invalid),
+    };
+}
+
+fn integerLiteral(self: *Self, first: u8) Token {
+    var value: usize = @intCast(digitValue(first).?);
+    while (digitValue(self.peek())) |d| {
+        _ = self.eat();
+        value = value *| 10 +| d;
+    }
+    return self.create(.{ .IntegerLiteral = value });
+}
+
+fn create(self: *Self, tajp: Token.Type) Token {
+    const start = self.last_end;
+    self.last_end = self.pos;
+    return .{ .start = start, .end = self.pos, .type = tajp };
+}
+
+fn eat(self: *Self) ?u8 {
+    const token = self.peek();
+    if (token != null) self.pos += 1;
+    return token;
+}
+
+fn peek(self: *Self) ?u8 {
+    return if (self.pos < self.source.len) self.source[self.pos] else null;
+}
+
+const Self = @This();
+
+fn digitValue(c: ?u8) ?u8 {
+    return switch (c orelse return null) {
+        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' => c.? - '0',
+        else => null,
+    };
+}
diff --git a/src/main.zig b/src/main.zig
new file mode 100644
index 0000000..e897d41
--- /dev/null
+++ b/src/main.zig
@@ -0,0 +1,46 @@
+pub const peekable = peek.peekable;
+pub const Peekable = peek.Peekable;
+
+pub fn main() !void {
+    var arena: std.heap.ArenaAllocator = .init(std.heap.smp_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+
+    var bw = std.io.bufferedWriter(std.io.getStdOut().writer());
+    const stdout = bw.writer();
+
+    // var br = std.io.bufferedReader(std.io.getStdIn().reader());
+    // const stdin = br.reader();
+    //
+    // var line: std.ArrayList(u8) = .init(alloc);
+    // defer line.deinit();
+    // while (true) {
+    //     try stdin.streamUntilDelimiter(line.writer(), '\n', null);
+    //
+    //     const lexer = Lexer{.source = line};
+    //
+    //     try stdout.print("{s}\n", .{line.items});
+    // }
+
+    const source = "69 + (32 + 1) + 2";
+    // var lexer = Lexer{ .source = source };
+    // while (true) {
+    //     const token = lexer.next().?;
+    //     try stdout.print("{}\n", .{token});
+    //     if (token.type == .Eof) break;
+    // }
+    // try stdout.print("\n", .{});
+    var lexer2 = peekable(Lexer{ .source = source });
+    try stdout.print("{}\n", .{try parse.expression(allocator, &lexer2)});
+
+    try bw.flush(); // Don't forget to flush!
+}
+
+const std = @import("std");
+const Lexer = @import("./lexer.zig");
+const parse = @import("./parse.zig");
+const peek = @import("./peek.zig");
+
+test {
+    _ = peek;
+}
diff --git a/src/parse.zig b/src/parse.zig
new file mode 100644
index 0000000..8ceabeb
--- /dev/null
+++ b/src/parse.zig
@@ -0,0 +1,50 @@
+pub const Expr = union(enum) {
+    IntegerLiteral: Token,
+    BinOp: struct { lhs: *const Expr, op: Token, rhs: *const Expr },
+    Invalid: Token,
+};
+
+pub fn expression(allocator: Allocator, lexer: *Peekable(Lexer)) error{OutOfMemory}!*Expr {
+    return addExpr(allocator, lexer);
+}
+
+pub fn addExpr(allocator: Allocator, lexer: *Peekable(Lexer)) !*Expr {
+    const lhs = try primaryExpr(allocator, lexer);
+    const token: ?Lexer.Token = lexer.peek();
+    const op = (if (token) |t| if (t.type == .Plus) t else null else null) orelse return lhs;
+    _ = lexer.next();
+
+    const rhs = try primaryExpr(allocator, lexer);
+    return allocate(allocator, .{ .BinOp = .{ .lhs = lhs, .op = op, .rhs = rhs } });
+}
+
+pub fn primaryExpr(allocator: Allocator, lexer: *Peekable(Lexer)) !*Expr {
+    const token = lexer.next().?;
+    // std.debug.print("term {}\n", .{token});
+    return allocate(allocator, switch (token.type) {
+        .LeftParen => {
+            const res = expression(allocator, lexer);
+            const right_paren = lexer.next().?;
+            if (right_paren.type != .RightParen)
+                return allocate(allocator, .{ .Invalid = right_paren });
+            return res;
+        },
+        .IntegerLiteral => .{ .IntegerLiteral = token },
+        else => .{ .Invalid = token },
+    });
+}
+
+fn allocate(allocator: Allocator, expr: Expr) !*Expr {
+    const res = try allocator.create(Expr);
+    res.* = expr;
+    return res;
+}
+
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+
+const Lexer = @import("./lexer.zig");
+const Token = Lexer.Token;
+const root = @import("root");
+const Peekable = root.Peekable;
+const peekable = root.peekable;
diff --git a/src/peek.zig b/src/peek.zig
new file mode 100644
index 0000000..58911e9
--- /dev/null
+++ b/src/peek.zig
@@ -0,0 +1,51 @@
+pub fn peekable(iterator: anytype) Peekable(@TypeOf(iterator)) {
+    return .{ .iterator = iterator };
+}
+
+pub fn Peekable(Iterator: type) type {
+    const ActualIterator = switch (@typeInfo(Iterator)) {
+        .pointer => |p| p.child,
+        else => Iterator,
+    };
+    const Next = @typeInfo(@TypeOf(ActualIterator.next)).@"fn";
+    const Item = switch (@typeInfo(Next.return_type.?)) {
+        .optional => |o| o.child,
+        else => |i| i,
+    };
+    return struct {
+        iterator: Iterator,
+        peeked: ?Item = null,
+
+        pub fn peek(self: *Self) ?Item {
+            if (self.peeked) |peeked| return peeked;
+            const item = self.iterator.next();
+            self.peeked = item;
+            return item;
+        }
+
+        pub fn next(self: *Self) ?Item {
+            const item = if (self.peeked) |peeked| peeked else self.iterator.next();
+            self.peeked = null;
+            return item;
+        }
+
+        const Self = @This();
+    };
+}
+
+test peekable {
+    const expect = std.testing.expect;
+    // std.meta.de
+
+    var it = std.mem.window(u8, &[_]u8{ 1, 2, 3 }, 1, 1);
+    var peek = peekable(&it);
+    try expect(peek.next().?[0] == 1);
+    try expect(peek.peek().?[0] == 2);
+    try expect(peek.peek().?[0] == 2);
+    try expect(peek.next().?[0] == 2);
+    try expect(peek.next().?[0] == 3);
+    try expect(peek.peek() == null);
+    try expect(peek.next() == null);
+}
+
+const std = @import("std");
-- 
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