diff --git a/lib/vaporware/compiler.rb b/lib/vaporware/compiler.rb
index 96f6493..bb270a6 100644
--- a/lib/vaporware/compiler.rb
+++ b/lib/vaporware/compiler.rb
@@ -40,7 +40,7 @@ def compile(compiler: "gcc", compiler_options: ["-O0"])
       end
       output.close
       compiler_options += @generator.compile_shared_option if @generator.shared
-      @generator.call_compiler(compiler:, compiler_options:)
+      @generator.to_elf(input: @generator.precompile, compiler:, compiler_options:, debug: @generator.debug)
     end
   end
 end
diff --git a/lib/vaporware/compiler/generator.rb b/lib/vaporware/compiler/generator.rb
index b0eb4eb..19f17d0 100644
--- a/lib/vaporware/compiler/generator.rb
+++ b/lib/vaporware/compiler/generator.rb
@@ -31,16 +31,22 @@ def register_var_and_method(node)
 
       def already_build_methods? = defined_methods.sort == @doned.to_a.sort
 
-      def call_compiler(output: precompile, compiler: "gcc", compiler_options: ["-O0"])
-        base_name = File.basename(output, ".*")
+      def to_elf(input: precompile, compiler: "gcc", compiler_options: ["-O0"], debug: false)
+        base_name = File.basename(input, ".*")
         name = shared ? "lib#{base_name}.so" : base_name
-        compile_commands = [compiler, *compiler_options, "-o", name, output].compact
-        IO.popen(compile_commands).close
+        if compiler.nil?
+          Vaporware::Compiler::Assemble.compile!(name, input)
+        else
+          compile_commands = [compiler, *compiler_options, "-o", name, input].compact
+          call_compiler(compile_commands)
+        end
 
-        File.delete(output) unless debug
+        File.delete(input) unless debug
         nil
       end
 
+      def call_compiler(compile_commands) = IO.popen(compile_commands).close
+
       def epilogue(output)
         output.puts "  mov rsp, rbp"
         output.puts "  pop rbp"
diff --git a/sig/vaporware.rbs b/sig/vaporware.rbs
index fb62e27..3e9535e 100644
--- a/sig/vaporware.rbs
+++ b/sig/vaporware.rbs
@@ -3,4 +3,57 @@ module Vaporware
   # See the writing guide of rbs: https://github.com/ruby/rbs#guides
   class Error
   end
+  class Compiler
+    # class methods
+    def self.compile: (String, ?compiler: String, ?dest: String, ?debug: bool, ?compiler_options: Array[String], ?shared: bool) -> nil
+    def initialize: (String, ?_precompile: String, ?debug: bool, ?shared: bool) -> untyped
+    @generator: Vaporware::Compiler::Generator
+    # instance methods
+    def compile: (?compiler: String, ?compiler_options: Array[String]) -> nil
+    class Generator
+      REGISTER: Array[String]
+      # instance variables
+      @precompile: String
+      @debug: bool
+      @doned: Set[Symbol]
+      @defined_methods: Set[Symbol]
+      @defined_variables: Set[Symbol]
+      @seq: Integer
+      @main: bool
+      @shared: bool
+      # temporarily using untyped types since parser.gem's rbs information is unchecked.
+      @ast: untyped
+      # class methods
+      def initialize: (String, precompile: String, debug: bool, shared: bool) -> untyped
+
+      # attr reader for instance variables
+      def precompile: -> String
+      def ast: -> untyped # Parser::AST::Node
+      def defined_methods: -> Set[Symbol]
+      def defined_variables: -> Set[Symbol]
+      def debug: -> bool
+      def doned: -> Set[Symbol]
+      def seq: -> Integer
+      def shared: -> bool
+      # instance private methods
+      def already_build_methods?: -> bool
+      def args: (untyped, File) -> nil
+      def build: (untyped, File, ?bool) -> nil
+      def call_compiler: (Array[String]) -> nil
+      def call_method: (untyped, File, bool) -> nil
+      def comp: (String, File) -> nil
+      def compile_shared_option: () -> Array[String]
+      def define_method_prologue: (untyped, File) -> nil
+      def epilogue: (File) -> nil
+      def lvar: (untyped, File) -> nil
+      def method: (Symbol, untyped, File) -> nil
+      def prologue: (untyped, File) -> nil
+      def prologue_methods: (File) -> nil
+      def ret: (File) -> nil
+      def lvar_offset: (Symbol | nil) -> Integer
+      def register_var_and_method: (untyped) -> nil
+      def to_elf: (?input: String, ?compiler: String, ?compiler_options: Array[String], ?debug: bool) -> nil
+      def variable_or_method?: (Symbol) -> bool
+    end
+  end
 end