diff --git a/lib/vaporware/compiler/assembler/elf/section/text.rb b/lib/vaporware/compiler/assembler/elf/section/text.rb
index 3f1777b..e660b6e 100644
--- a/lib/vaporware/compiler/assembler/elf/section/text.rb
+++ b/lib/vaporware/compiler/assembler/elf/section/text.rb
@@ -43,7 +43,7 @@ def opecode(op, *operands)
     when "ret"
       [0xc3]
     else
-      raise Compiler::Assembler::ERROR
+      raise Vaporware::Compiler::Assembler::ELF::Error, "yet implemented operations: #{op}"
     end
   end
 
@@ -99,16 +99,18 @@ def pop(operands)
 
   def reg(r)
     case r
-    in "rsp"
+    when "rsp"
       0xec
-    in "rbp"
+    when "rbp"
       0x5e
-    in "rax"
+    when "rax"
       0x29
-    in "rdi"
+    when "rdi"
       0xf8
-    in /\d+/
+    when /\d+/
       ("%02x" % r).to_i(16)
+    else
+      raise Vaporware::Compiler::Assembler::ELF::Error, "yet implemented operand address: #{r}"
     end
   end
 end
diff --git a/sig/vaporware/compiler/assembler/elf.rbs b/sig/vaporware/compiler/assembler/elf.rbs
index ba3e3cb..dd644c5 100644
--- a/sig/vaporware/compiler/assembler/elf.rbs
+++ b/sig/vaporware/compiler/assembler/elf.rbs
@@ -1,4 +1,3 @@
 class Vaporware::Compiler::Assembler::ELF
-  class Error
-  end
+  Error: singleton(StandardError)
 end
diff --git a/sig/vaporware/compiler/assembler/elf/section/text.rbs b/sig/vaporware/compiler/assembler/elf/section/text.rbs
index 26926ac..bc41571 100644
--- a/sig/vaporware/compiler/assembler/elf/section/text.rbs
+++ b/sig/vaporware/compiler/assembler/elf/section/text.rbs
@@ -3,18 +3,18 @@ class Vaporware::Compiler::Assembler::ELF::Section::Text
   REGISTER_CODE: Hash[Symbol, Integer]
   OPECODE: Hash[Symbol, Integer]
 
-  @bytes: Array[untyped]?
+  @bytes: Array[untyped]
 
-  attr_reader size: Integer
   attr_reader offset: Integer
 
   def initialize: () -> void
   def assemble!: (String) -> void
   def align!: (Integer) -> void
+  def build: () -> String
 
   private
 
-  def opecode: ((String | Symbol), Array[String]) -> (Array[Integer] | nil)
+  def opecode: ((String | Symbol)?, *String) -> Array[Integer]
   def mov: ((String | Symbol), Array[String]) -> Array[Integer]
   def calc: ((String | Symbol), Array[String]) -> Array[Integer]
   def push: (Array[String]) -> Array[Integer]