diff --git a/src/crisp/core.cr b/src/crisp/core.cr
index 5ad38a3..aaaa01c 100644
--- a/src/crisp/core.cr
+++ b/src/crisp/core.cr
@@ -43,7 +43,7 @@ module Crisp
   end
 
   def pr_str(args)
-    args.map{|a| Priter.new.print(a)}.join(" ")
+    args.map{|a| Printer.new.print(a)}.join(" ")
   end
 
   def str(args)
diff --git a/src/crisp/error.cr b/src/crisp/error.cr
index b9a2a49..5d02374 100644
--- a/src/crisp/error.cr
+++ b/src/crisp/error.cr
@@ -1,4 +1,6 @@
 module Crisp
+  extend self
+
   class ParseException < Exception
   end
 
diff --git a/src/crisp/interpreter.cr b/src/crisp/interpreter.cr
index c9ad86c..93931a6 100644
--- a/src/crisp/interpreter.cr
+++ b/src/crisp/interpreter.cr
@@ -14,7 +14,7 @@ require "./error"
 module Crisp
 
   class Interpreter
-    def initialize(args)
+    def initialize(args = nil)
       @env = Crisp::Env.new
 
       Crisp::NameSpace.each{|k,v| @curent_env.set(k, Crisp::Type.new(v))}
diff --git a/src/crisp/printer.cr b/src/crisp/printer.cr
index 237afea..1b0716e 100644
--- a/src/crisp/printer.cr
+++ b/src/crisp/printer.cr
@@ -10,14 +10,14 @@ module Crisp
         when Nil          then "nil"
         when Bool         then value.to_s
         when Int32        then value.to_s
-        when Crisp::List    then "(#{value.map{|v| pr_str(v, @print_readably) as String}.join(" ")})"
-        when Crisp::Vector  then "[#{value.map{|v| pr_str(v, @print_readably) as String}.join(" ")}]"
+        when Crisp::List    then "(#{value.map{|v| print(v) as String}.join(" ")})"
+        when Crisp::Vector  then "[#{value.map{|v| print(v) as String}.join(" ")}]"
         when Crisp::Symbol  then value.str.to_s
         when Crisp::Func    then "<function>"
         when Crisp::Closure then "<closure>"
         when Crisp::HashMap
         # step1_read_print.cr requires specifying type
-        "{#{value.map{|k, v| "#{pr_str(k, @print_readably)} #{pr_str(v, @print_readably)}" as String}.join(" ")}}"
+        "{#{value.map{|k, v| "#{print(k)} #{print(v)}"}.join(" ")}}"
         when String
         case
         when value.empty?()
@@ -28,14 +28,14 @@ module Crisp
             @print_readably ? value.inspect : value
         end
         when Crisp::Atom
-        "(atom #{pr_str(value.val, @print_readably)})"
+        "(atom #{print(value.val)})"
         else
         raise "invalid CrispType: #{value.to_s}"
         end
     end
 
     def print(t : Crisp::Type)
-        print(t.unwrap, @print_readably) + (t.macro? ? " (macro)" : "")
+        print(t.unwrap) + (t.macro? ? " (macro)" : "")
     end
   end
 end