4 files changed, 213 insertions, 0 deletions
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");