diff --git a/README.md b/README.md
index 8e51aea..fe487a6 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,5 @@
 # Zig CLI
 
-A command argument parser library for Zig.
+A command argument parser library for Zig. Now it's in a heavy development.
+
+See `demo.zig` for the usage.
diff --git a/build.zig b/build.zig
index 184ebb1..8e1e579 100644
--- a/build.zig
+++ b/build.zig
@@ -1,18 +1,39 @@
 const std = @import("std");
 
 pub fn build(b: *std.Build) void {
-    // b.addModule("cli", .{ .source_file = .{ .path = "cli.zig" } });
-
     const target = b.standardTargetOptions(.{});
     const optimize = b.standardOptimizeOption(.{});
 
+    const cli_mod = b.addModule("cli", .{ .root_source_file = .{ .path = "cli.zig" } });
+    const demo_exe = b.addExecutable(.{
+        .name = "cli-demo",
+        .root_source_file = .{ .path = "demo.zig" },
+        .optimize = optimize,
+        .target = target,
+        .link_libc = true,
+    });
+    demo_exe.root_module.addImport("cli", cli_mod);
+
+    // compile
+    const compile_step = b.step("compile", "Compile demo executable");
+    compile_step.dependOn(&demo_exe.step);
+
+    // install
+    b.installArtifact(demo_exe);
+
+    // run test
+    const run_demo_exe1 = b.addRunArtifact(demo_exe);
+    run_demo_exe1.addArgs(&[_][]const u8{ "-e", "4" });
+    const run_demo_exe2 = b.addRunArtifact(demo_exe);
+    run_demo_exe2.addArgs(&[_][]const u8{"subexample"});
     const unit_tests = b.addTest(.{
         .root_source_file = .{ .path = "cli.zig" },
         .target = target,
         .optimize = optimize,
     });
-
     const run_unit_tests = b.addRunArtifact(unit_tests);
     const test_step = b.step("test", "Run unit tests");
     test_step.dependOn(&run_unit_tests.step);
+    test_step.dependOn(&run_demo_exe1.step);
+    test_step.dependOn(&run_demo_exe2.step);
 }
diff --git a/build.zig.zon b/build.zig.zon
new file mode 100644
index 0000000..41f2968
--- /dev/null
+++ b/build.zig.zon
@@ -0,0 +1,12 @@
+.{
+    .name = "zig-cli",
+    .version = "0.0.1",
+    .paths = .{
+        "README.md",
+        "build.zig",
+        "build.zig.zon",
+        "util.zig",
+        "cli.zig",
+        "demo.zig",
+    },
+}
diff --git a/cli.zig b/cli.zig
index 6912efc..6ee7fde 100644
--- a/cli.zig
+++ b/cli.zig
@@ -1,77 +1,199 @@
 const std = @import("std");
-const heap = std.heap;
+const io = std.io;
 const mem = std.mem;
 const process = std.process;
-const testing = std.testing;
-const Allocator = std.mem.Allocator;
-const Arena = std.heap.ArenaAllocator;
+const ArrayList = std.ArrayList;
+const StringHashMap = std.StringHashMap;
+const util = @import("./util.zig");
 
-pub fn Option(T: type) Option {
-    return struct {
-        const Self = @This();
-        const Action = fn (e: T) void;
+pub const Option = struct {
+    short: []const u8,
+    long: []const u8,
+    optional: bool,
+    global: bool,
+    description: []const u8,
+    value_string: []const u8 = "",
+    value_int: i32 = 0,
+    value_float: f32 = 0.0,
+    value_bool: bool = false,
+    value_type: ValueType,
 
-        short: []const u8,
-        long: []const u8,
-        description: []const u8,
-        value: T,
-        action: Action,
+    const ValueType = enum {
+        STRING,
+        BOOL,
+        INT,
+        FLOAT,
     };
-}
+};
 
 pub const Command = struct {
-    name: []const u8,
-    commands: std.ArrayList(*Command),
-    options: std.ArrayList(*Option),
-    allocator: *Allocator,
+    const Commands = StringHashMap(Command);
+    const Options = StringHashMap(Option);
+    const Args = ArrayList([]const u8);
+    pub const CommandConfig = struct {
+        name: []const u8,
+        short_description: []const u8,
+        long_description: []const u8,
+        usage: []const u8,
+        version: []const u8 = "0.0.1",
+        run: *const fn (cmd: *Command) void = undefined,
+    };
 
-    pub fn init(name: []const u8, allocator: *Allocator) Command {
-        const command = Command{
-            .name = name,
+    subcommands: Commands,
+    options: Options,
+    arguments: Args,
+    cmd_args: Args,
+    allocator: mem.Allocator,
+    config: CommandConfig,
+
+    pub fn init(allocator: mem.Allocator, args: CommandConfig) Command {
+        return Command{
+            .subcommands = Commands.init(allocator),
+            .options = Options.init(allocator),
+            .arguments = Args.init(allocator),
+            .cmd_args = Args.init(allocator),
             .allocator = allocator,
+            .config = args,
         };
-        command.commands = std.ArrayList(*Command).init(command.allocator);
-        command.options = std.ArrayList(*Option).init(command.allocator);
-        return command;
     }
 
     pub fn deinit(self: *Command) void {
-        self.commands.deinit();
+        self.subcommands.deinit();
         self.options.deinit();
+        self.arguments.deinit();
+        self.cmd_args.deinit();
     }
 
-    pub fn addCommand(self: *Command, command: *Command) void {
-        _ = command;
-        _ = self;
+    pub fn addOption(self: *Command, option: Option) !void {
+        try self.options.put(option.long, option);
     }
 
-    pub fn addOption(self: *Command, option: *Option) void {
-        _ = option;
-        _ = self;
+    pub fn addCommand(self: *Command, command: Command) !void {
+        try self.subcommands.put(command.config.name, command);
     }
-};
 
-pub const Parser = struct {
-    allocator: *Allocator,
-    command: Command,
+    pub fn help(self: *Command) !void {
+        const description = if (self.config.long_description.len > 0)
+            self.config.long_description
+        else if (self.config.short_description.len > 0)
+            self.config.short_description
+        else
+            self.config.name;
 
-    pub fn parse(self: *Parser, argsIterator: process.ArgIterator) void {
-        _ = self;
-        _ = argsIterator.skip();
-        for (argsIterator.next()) |arg| {
-            _ = arg;
+        var builder = ArrayList(u8).init(self.allocator);
+        defer builder.deinit();
+        try builder.appendSlice(description);
+        try builder.appendSlice("\n\n");
+        try builder.appendSlice("Usage: ");
+        try builder.appendSlice(self.config.usage);
+        try builder.appendSlice("\n\n");
+
+        if (self.subcommands.count() > 0) {
+            try builder.appendSlice("Subcommands: \n");
+            var entry_iterator = self.subcommands.iterator();
+            while (entry_iterator.next()) |subcommand| {
+                try builder.appendSlice("    ");
+                try builder.appendSlice(subcommand.key_ptr.*);
+                try builder.appendSlice("\t\t\t");
+                try builder.appendSlice(subcommand.value_ptr.*.config.short_description);
+                try builder.appendSlice("\n");
+            }
+            try builder.appendSlice("\n");
         }
+
+        if (self.options.count() > 0) {
+            try builder.appendSlice("Options: \n");
+            var entry_iterator = self.options.iterator();
+            while (entry_iterator.next()) |entry| {
+                const option = entry.value_ptr.*;
+                try builder.appendSlice("    -");
+                try builder.appendSlice(option.short);
+                try builder.appendSlice(", --");
+                try builder.appendSlice(option.long);
+                try builder.appendSlice("\t\t");
+                try builder.appendSlice(option.description);
+                if (!option.optional) {
+                    try builder.appendSlice(" (required)");
+                }
+                try builder.appendSlice("\n");
+            }
+        }
+        _ = try io.getStdOut().write(builder.items);
+    }
+
+    pub fn printVersion(self: *Command) !void {
+        _ = try io.getStdOut().write(try mem.concat(self.allocator, u8, &[_][]const u8{ self.config.version, "\n" }));
+    }
+
+    fn parse(self: *Command) !void {
+        var i: usize = 0;
+        var current_command = self.*;
+        var current_option: Option = undefined;
+        var parsing_option = false;
+        parse_while_blk: while (i < self.cmd_args.items.len) {
+            const current_arg = self.cmd_args.items[i];
+            if (!parsing_option) {
+                if (current_command.subcommands.get(current_arg)) |subcommand| {
+                    current_command = subcommand;
+                    i += 1;
+                    continue :parse_while_blk;
+                }
+            }
+            var entry_iterator = current_command.options.iterator();
+            while (entry_iterator.next()) |entry| {
+                const option = entry.value_ptr.*;
+                if (parsing_option) {
+                    switch (current_option.value_type) {
+                        .STRING => current_option.value_string = current_arg,
+                        .INT => current_option.value_int = util.strToInt(current_arg.ptr),
+                        .FLOAT => current_option.value_float = util.strToFloat(current_arg.ptr),
+                        else => {},
+                    }
+                    try self.options.put(entry.key_ptr.*, current_option);
+                    parsing_option = false;
+                    i += 1;
+                    continue :parse_while_blk;
+                } else if (mem.eql(u8, current_arg, try mem.concat(self.allocator, u8, &[_][]const u8{ "-", option.short })) or
+                    mem.eql(u8, current_arg, try mem.concat(self.allocator, u8, &[_][]const u8{ "--", option.long })))
+                {
+                    current_option = option;
+                    parsing_option = true;
+                    if (current_option.value_type == .BOOL) {
+                        current_option.value_bool = true;
+                        try self.options.put(entry.key_ptr.*, current_option);
+                        parsing_option = false;
+                    }
+                    i += 1;
+                    continue :parse_while_blk;
+                }
+            }
+            try self.arguments.append(current_arg);
+            i += 1;
+        }
+        current_command.config.run(&current_command);
+    }
+
+    pub fn execute(self: *Command) !void {
+        var arg_iterator = process.args();
+        while (arg_iterator.next()) |arg| {
+            try self.cmd_args.append(arg);
+        }
+        try self.parse();
+    }
+
+    pub fn getBoolOption(self: *Command, option_name: []const u8) bool {
+        return if (self.options.get(option_name)) |option| option.value_bool else false;
+    }
+
+    pub fn getStringOption(self: *Command, option_name: []const u8) []const u8 {
+        return if (self.options.get(option_name)) |option| option.value_string else "";
+    }
+
+    pub fn getIntOption(self: *Command, option_name: []const u8) i32 {
+        return if (self.options.get(option_name)) |option| option.value_int else 0;
+    }
+
+    pub fn getFloatOption(self: *Command, option_name: []const u8) f32 {
+        return if (self.options.get(option_name)) |option| option.value_float else 0.0;
     }
 };
-
-test {
-    const argsIterator = process.args();
-    const arena = Arena.init(heap.page_allocator);
-    const allocator = arena.child_allocator;
-    defer arena.deinit();
-
-    const command = Command{ .name = "test" };
-
-    const parser = Parser{ .allocator = allocator, .command = command };
-    parser.parse(argsIterator);
-}
diff --git a/demo.zig b/demo.zig
new file mode 100644
index 0000000..139b171
--- /dev/null
+++ b/demo.zig
@@ -0,0 +1,46 @@
+const std = @import("std");
+const heap = std.heap;
+const cli = @import("cli");
+const Command = cli.Command;
+const Option = cli.Option;
+
+fn rootRun(cmd: *Command) void {
+    const e = cmd.getIntOption("example");
+    std.debug.print("{d}\n", .{e});
+}
+
+fn subcommandRun(cmd: *Command) void {
+    std.debug.print("{s}\n", .{cmd.config.name});
+}
+
+pub fn main() !void {
+    var gpa = heap.GeneralPurposeAllocator(.{}){};
+    const allocator = gpa.allocator();
+    const config = Command.CommandConfig{
+        .short_description = "Example",
+        .long_description = "Example command",
+        .usage = "example",
+        .name = "example",
+        .run = rootRun,
+    };
+    var root_command = Command.init(allocator, config);
+    try root_command.addCommand(Command.init(allocator, .{
+        .short_description = "SubExample",
+        .long_description = "Subcommand example",
+        .usage = "subexample",
+        .name = "subexample",
+        .run = subcommandRun,
+    }));
+    try root_command.addOption(Option{
+        .short = "e",
+        .long = "example",
+        .description = "example option",
+        .optional = false,
+        .global = false,
+        .value_type = .INT,
+        .value_int = 3,
+    });
+    try root_command.execute();
+    try root_command.help();
+    try root_command.printVersion();
+}
diff --git a/util.zig b/util.zig
new file mode 100644
index 0000000..cec9d3a
--- /dev/null
+++ b/util.zig
@@ -0,0 +1,18 @@
+const std = @import("std");
+const testing = std.testing;
+const stdlib = @cImport({
+    @cInclude("stdlib.h");
+});
+
+pub fn strToFloat(str: [*c]const u8) f32 {
+    return @floatCast(stdlib.atof(str));
+}
+
+pub fn strToInt(str: [*c]const u8) i32 {
+    return @intCast(stdlib.atoi(str));
+}
+
+test "string cast to number" {
+    try testing.expect(3 == strToInt("3"));
+    try testing.expect(3.2 == strToFloat("3.2"));
+}