commit 7fd4ac01853765d8f41fcb8dd38ef5b933f21a0e
Author: rhysd <lin90162@yahoo.co.jp>
Date:   Thu Jun 4 00:35:19 2015 +0900

    import from my Mal implementation

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..d1f2bed
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+.crystal
diff --git a/src/core.cr b/src/core.cr
new file mode 100644
index 0000000..15f870d
--- /dev/null
+++ b/src/core.cr
@@ -0,0 +1,413 @@
+require "time"
+
+require "./types"
+require "./error"
+require "./printer"
+require "./reader"
+require "./readline"
+
+module Mal
+
+macro calc_op(op)
+  -> (args : Array(Mal::Type)) {
+    x, y = args[0].unwrap, args[1].unwrap
+    eval_error "invalid arguments for binary operator {{op.id}}" unless x.is_a?(Int32) && y.is_a?(Int32)
+    Mal::Type.new(x {{op.id}} y)
+  }
+end
+
+def self.list(args)
+  args.to_mal
+end
+
+def self.list?(args)
+  args.first.unwrap.is_a? Mal::List
+end
+
+def self.empty?(args)
+  a = args.first.unwrap
+  a.is_a?(Array) ? a.empty? : false
+end
+
+def self.count(args)
+  a = args.first.unwrap
+  case a
+  when Array
+    a.size as Int32
+  when Nil
+    0
+  else
+    eval_error "invalid argument for function 'count'"
+  end
+end
+
+def self.pr_str_(args)
+  args.map{|a| pr_str(a)}.join(" ")
+end
+
+def self.str(args)
+  args.map{|a| pr_str(a, false)}.join
+end
+
+def self.prn(args)
+  puts self.pr_str_(args)
+  nil
+end
+
+def self.println(args)
+  puts args.map{|a| pr_str(a, false)}.join(" ")
+  nil
+end
+
+def self.read_string(args)
+  head = args.first.unwrap
+  eval_error "argument of read-str must be string" unless head.is_a? String
+  read_str head
+end
+
+def self.slurp(args)
+  head = args.first.unwrap
+  eval_error "argument of slurp must be string" unless head.is_a? String
+  begin
+    File.read head
+  rescue e : Errno
+    eval_error "no such file"
+  end
+end
+
+def self.cons(args)
+  head, tail = args[0] as Mal::Type, args[1].unwrap
+  eval_error "2nd arg of cons must be list" unless tail.is_a? Array
+  ([head] + tail).to_mal
+end
+
+def self.concat(args)
+  args.each_with_object(Mal::List.new) do |arg, list|
+    a = arg.unwrap
+    eval_error "arguments of concat must be list" unless a.is_a?(Array)
+    a.each{|e| list << e}
+  end
+end
+
+def self.nth(args)
+  a0, a1 = args[0].unwrap, args[1].unwrap
+  eval_error "1st argument of nth must be list or vector" unless a0.is_a? Array
+  eval_error "2nd argument of nth must be integer" unless a1.is_a? Int32
+  a0[a1]
+end
+
+def self.first(args)
+  a0 = args[0].unwrap
+
+  return nil if a0.nil?
+  eval_error "1st argument of first must be list or vector or nil" unless a0.is_a? Array
+  a0.empty? ? nil : a0.first
+end
+
+def self.rest(args)
+  a0 = args[0].unwrap
+
+  return Mal::List.new if a0.nil?
+  eval_error "1st argument of first must be list or vector or nil" unless a0.is_a? Array
+  return Mal::List.new if a0.empty?
+  a0[1..-1].to_mal
+end
+
+def self.apply(args)
+  eval_error "apply must take at least 2 arguments" unless args.size >= 2
+
+  head = args.first.unwrap
+  last = args.last.unwrap
+
+  eval_error "last argument of apply must be list or vector" unless last.is_a? Array
+
+  case head
+  when Mal::Closure
+    head.fn.call(args[1..-2] + last)
+  when Mal::Func
+    head.call(args[1..-2] + last)
+  else
+    eval_error "1st argument of apply must be function or closure"
+  end
+end
+
+def self.map(args)
+  func = args.first.unwrap
+  list = args[1].unwrap
+
+  eval_error "2nd argument of map must be list or vector" unless list.is_a? Array
+
+  f = case func
+      when Mal::Closure then func.fn
+      when Mal::Func    then func
+      else                   eval_error "1st argument of map must be function"
+      end
+
+  list.each_with_object(Mal::List.new) do |elem, mapped|
+    mapped << f.call([elem])
+  end
+end
+
+def self.nil?(args)
+  args.first.unwrap.nil?
+end
+
+def self.true?(args)
+  a = args.first.unwrap
+  a.is_a?(Bool) && a
+end
+
+def self.false?(args)
+  a = args.first.unwrap
+  a.is_a?(Bool) && !a
+end
+
+def self.symbol?(args)
+  args.first.unwrap.is_a?(Mal::Symbol)
+end
+
+def self.symbol(args)
+  head = args.first.unwrap
+  eval_error "1st argument of symbol function must be string" unless head.is_a? String
+  Mal::Symbol.new head
+end
+
+def self.keyword(args)
+  head = args.first.unwrap
+  eval_error "1st argument of symbol function must be string" unless head.is_a? String
+  "\u029e" + head
+end
+
+def self.keyword?(args)
+  head = args.first.unwrap
+  head.is_a?(String) && !head.empty? && head[0] == '\u029e'
+end
+
+def self.vector(args)
+  args.to_mal(Mal::Vector)
+end
+
+def self.vector?(args)
+  args.first.unwrap.is_a? Mal::Vector
+end
+
+def self.hash_map(args)
+  eval_error "hash-map must take even number of arguments" unless args.size.even?
+  map = Mal::HashMap.new
+  args.each_slice(2) do |kv|
+    k = kv[0].unwrap
+    eval_error "key must be string" unless k.is_a? String
+    map[k] = kv[1]
+  end
+  map
+end
+
+def self.map?(args)
+  args.first.unwrap.is_a? Mal::HashMap
+end
+
+def self.assoc(args)
+  head = args.first.unwrap
+  eval_error "1st argument of assoc must be hashmap" unless head.is_a? Mal::HashMap
+  eval_error "assoc must take a list and even number of arguments" unless (args.size - 1).even?
+
+  map = Mal::HashMap.new
+  head.each{|k, v| map[k] = v}
+
+  args[1..-1].each_slice(2) do |kv|
+    k = kv[0].unwrap
+    eval_error "key must be string" unless k.is_a? String
+    map[k] = kv[1]
+  end
+
+  map
+end
+
+def self.dissoc(args)
+  head = args.first.unwrap
+  eval_error "1st argument of assoc must be hashmap" unless head.is_a? Mal::HashMap
+
+  map = Mal::HashMap.new
+  head.each{|k,v| map[k] = v}
+
+  args[1..-1].each do |arg|
+    key = arg.unwrap
+    eval_error "key must be string" unless key.is_a? String
+    map.delete key
+  end
+
+  map
+end
+
+def self.get(args)
+  a0, a1 = args[0].unwrap, args[1].unwrap
+  return nil unless a0.is_a? Mal::HashMap
+  eval_error "2nd argument of get must be string" unless a1.is_a? String
+
+  # a0[a1]? isn't available because type ofa0[a1] is infered NoReturn
+  a0.has_key?(a1) ? a0[a1] : nil
+end
+
+def self.contains?(args)
+  a0, a1 = args[0].unwrap, args[1].unwrap
+  eval_error "1st argument of get must be hashmap" unless a0.is_a? Mal::HashMap
+  eval_error "2nd argument of get must be string" unless a1.is_a? String
+  a0.has_key? a1
+end
+
+def self.keys(args)
+  head = args.first.unwrap
+  eval_error "1st argument of assoc must be hashmap" unless head.is_a? Mal::HashMap
+  head.keys.each_with_object(Mal::List.new){|e,l| l << Mal::Type.new(e)}
+end
+
+def self.vals(args)
+  head = args.first.unwrap
+  eval_error "1st argument of assoc must be hashmap" unless head.is_a? Mal::HashMap
+  head.values.to_mal
+end
+
+def self.sequential?(args)
+  args.first.unwrap.is_a? Array
+end
+
+def self.readline(args)
+  head = args.first.unwrap
+  eval_error "1st argument of readline must be string" unless head.is_a? String
+  my_readline head
+end
+
+def self.meta(args)
+  m = args.first.meta
+  m.nil? ? nil : m
+end
+
+def self.with_meta(args)
+  t = args.first.dup
+  t.meta = args[1]
+  t
+end
+
+def self.atom(args)
+  Mal::Atom.new args.first
+end
+
+def self.atom?(args)
+  args.first.unwrap.is_a? Mal::Atom
+end
+
+def self.deref(args)
+  head = args.first.unwrap
+  eval_error "1st argument of deref must be atom" unless head.is_a? Mal::Atom
+  head.val
+end
+
+def self.reset!(args)
+  head = args.first.unwrap
+  eval_error "1st argument of reset! must be atom" unless head.is_a? Mal::Atom
+  head.val = args[1]
+end
+
+def self.swap!(args)
+  atom = args.first.unwrap
+  eval_error "1st argument of swap! must be atom" unless atom.is_a? Mal::Atom
+
+  a = [atom.val] + args[2..-1]
+
+  func = args[1].unwrap
+  case func
+  when Mal::Func
+    atom.val = func.call a
+  when Mal::Closure
+    atom.val = func.fn.call a
+  else
+    eval_error "2nd argumetn of swap! must be function"
+  end
+end
+
+def self.conj(args)
+  seq = args.first.unwrap
+  case seq
+  when Mal::List
+    (args[1..-1].reverse + seq).to_mal
+  when Mal::Vector
+    (seq + args[1..-1]).to_mal(Mal::Vector)
+  else
+    eval_error "1st argument of conj must be list or vector"
+  end
+end
+
+def self.time_ms(args)
+  (Time.now.to_i.to_i32) * 1000
+end
+
+# Note:
+# Simply using ->self.some_func doesn't work
+macro func(name)
+  -> (args : Array(Mal::Type)) { Mal::Type.new self.{{name.id}}(args) }
+end
+
+macro rel_op(op)
+-> (args : Array(Mal::Type)) { Mal::Type.new (args[0] {{op.id}} args[1]) }
+end
+
+NS = {
+  "+"           => calc_op(:+)
+  "-"           => calc_op(:-)
+  "*"           => calc_op(:*)
+  "/"           => calc_op(:/)
+  "list"        => func(:list)
+  "list?"       => func(:list?)
+  "empty?"      => func(:empty?)
+  "count"       => func(:count)
+  "="           => rel_op(:==)
+  "<"           => rel_op(:<)
+  ">"           => rel_op(:>)
+  "<="          => rel_op(:<=)
+  ">="          => rel_op(:>=)
+  "pr-str"      => func(:pr_str_)
+  "str"         => func(:str)
+  "prn"         => func(:prn)
+  "println"     => func(:println)
+  "read-string" => func(:read_string)
+  "slurp"       => func(:slurp)
+  "cons"        => func(:cons)
+  "concat"      => func(:concat)
+  "nth"         => func(:nth)
+  "first"       => func(:first)
+  "rest"        => func(:rest)
+  "throw"       => -> (args : Array(Mal::Type)) { raise Mal::RuntimeException.new args[0] }
+  "apply"       => func(:apply)
+  "map"         => func(:map)
+  "nil?"        => func(:nil?)
+  "true?"       => func(:true?)
+  "false?"      => func(:false?)
+  "symbol?"     => func(:symbol?)
+  "symbol"      => func(:symbol)
+  "keyword"     => func(:keyword)
+  "keyword?"    => func(:keyword?)
+  "vector"      => func(:vector)
+  "vector?"     => func(:vector?)
+  "hash-map"    => func(:hash_map)
+  "map?"        => func(:map?)
+  "assoc"       => func(:assoc)
+  "dissoc"      => func(:dissoc)
+  "get"         => func(:get)
+  "contains?"   => func(:contains?)
+  "keys"        => func(:keys)
+  "vals"        => func(:vals)
+  "sequential?" => func(:sequential?)
+  "readline"    => func(:readline)
+  "meta"        => func(:meta)
+  "with-meta"   => func(:with_meta)
+  "atom"        => func(:atom)
+  "atom?"       => func(:atom?)
+  "deref"       => func(:deref)
+  "deref"       => func(:deref)
+  "reset!"      => func(:reset!)
+  "swap!"       => func(:swap!)
+  "conj"        => func(:conj)
+  "time-ms"     => func(:time_ms)
+} of String => Mal::Func
+
+end
diff --git a/src/env.cr b/src/env.cr
new file mode 100644
index 0000000..9f38d68
--- /dev/null
+++ b/src/env.cr
@@ -0,0 +1,68 @@
+require "./types"
+require "./error"
+
+module Mal
+
+  class Env
+    property data
+
+    def initialize(@outer)
+      @data = {} of String => Mal::Type
+    end
+
+    def initialize(@outer, binds, exprs : Array(Mal::Type))
+      @data = {} of String => Mal::Type
+
+      eval_error "binds must be list or vector" unless binds.is_a? Array
+
+      # Note:
+      # Array#zip() can't be used because overload resolution failed
+      (0...binds.size).each do |idx|
+        sym = binds[idx].unwrap
+        eval_error "bind name must be symbol" unless sym.is_a? Mal::Symbol
+
+        if sym.str == "&"
+          eval_error "missing variable parameter name" if binds.size == idx
+          next_param = binds[idx+1].unwrap
+          eval_error "bind name must be symbol" unless next_param.is_a? Mal::Symbol
+          var_args = Mal::List.new
+          exprs[idx..-1].each{|e| var_args << e} if idx < exprs.size
+          @data[next_param.str] = Mal::Type.new var_args
+          break
+        end
+
+        @data[sym.str] = exprs[idx]
+      end
+    end
+
+    def dump
+      puts "ENV BEGIN".colorize.red
+      @data.each do |k, v|
+        puts "  #{k} -> #{print(v)}".colorize.red
+      end
+      puts "ENV END".colorize.red
+    end
+
+    def set(key, value)
+      @data[key] = value
+    end
+
+    def find(key)
+      return self if @data.has_key? key
+
+      o = @outer
+      if o
+        o.find key
+      else
+        nil
+      end
+    end
+
+    def get(key)
+      e = find key
+      eval_error "'#{key}' not found" unless e
+      e.data[key]
+    end
+  end
+
+end
diff --git a/src/error.cr b/src/error.cr
new file mode 100644
index 0000000..6df309d
--- /dev/null
+++ b/src/error.cr
@@ -0,0 +1,22 @@
+module Mal
+  class ParseException < Exception
+  end
+
+  class EvalException < Exception
+  end
+
+  class RuntimeException < Exception
+    getter :thrown
+    def initialize(@thrown)
+      super()
+    end
+  end
+end
+
+def eval_error(msg)
+  raise Mal::EvalException.new msg
+end
+
+def parse_error(msg)
+  raise Mal::ParseException.new msg
+end
diff --git a/src/printer.cr b/src/printer.cr
new file mode 100644
index 0000000..7444cb2
--- /dev/null
+++ b/src/printer.cr
@@ -0,0 +1,34 @@
+require "./types"
+
+def pr_str(value, print_readably = true)
+  case value
+  when Nil          then "nil"
+  when Bool         then value.to_s
+  when Int32        then value.to_s
+  when Mal::List    then "(#{value.map{|v| pr_str(v, print_readably) as String}.join(" ")})"
+  when Mal::Vector  then "[#{value.map{|v| pr_str(v, print_readably) as String}.join(" ")}]"
+  when Mal::Symbol  then value.str.to_s
+  when Mal::Func    then "<function>"
+  when Mal::Closure then "<closure>"
+  when Mal::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(" ")}}"
+  when String
+    case
+    when value.empty?()
+      print_readably ? value.inspect : value
+    when value[0] == '\u029e'
+      ":#{value[1..-1]}"
+    else
+      print_readably ? value.inspect : value
+    end
+  when Mal::Atom
+    "(atom #{pr_str(value.val, print_readably)})"
+  else
+    raise "invalid MalType: #{value.to_s}"
+  end
+end
+
+def pr_str(t : Mal::Type, print_readably = true)
+  pr_str(t.unwrap, print_readably) + (t.macro? ? " (macro)" : "")
+end
diff --git a/src/reader.cr b/src/reader.cr
new file mode 100644
index 0000000..74a5605
--- /dev/null
+++ b/src/reader.cr
@@ -0,0 +1,137 @@
+require "./types"
+require "./error"
+
+class Reader
+  def initialize(@tokens)
+    @pos = 0
+  end
+
+  def current_token
+    @tokens[@pos] rescue nil
+  end
+
+  def peek
+    t = current_token
+
+    if t && t[0] == ';'
+      @pos += 1
+      peek
+    else
+      t
+    end
+  end
+
+  def next
+    peek
+  ensure
+    @pos += 1
+  end
+
+  def read_sequence(init, open, close)
+    token = self.next
+    parse_error "expected '#{open}', got EOF" unless token
+    parse_error "expected '#{open}', got #{token}" unless  token[0] == open
+
+    loop do
+      token = peek
+      parse_error "expected '#{close}', got EOF" unless token
+      break if token[0] == close
+
+      init << read_form
+      peek
+    end
+
+    self.next
+    init
+  end
+
+  def read_list
+    Mal::Type.new read_sequence(Mal::List.new, '(', ')')
+  end
+
+  def read_vector
+    Mal::Type.new read_sequence(Mal::Vector.new, '[', ']')
+  end
+
+  def read_hashmap
+    types = read_sequence([] of Mal::Type, '{', '}')
+
+    parse_error "odd number of elements for hash-map: #{types.size}" if types.size.odd?
+    map = Mal::HashMap.new
+
+    types.each_slice(2) do |kv|
+      k, v = kv[0].unwrap, kv[1]
+      case k
+      when String
+        map[k] = v
+      else
+        parse_error("key of hash-map must be string or keyword")
+      end
+    end
+
+    Mal::Type.new map
+  end
+
+  def read_atom
+    token = self.next
+    parse_error "expected Atom but got EOF" unless token
+
+    Mal::Type.new case
+    when token =~ /^-?\d+$/ then token.to_i
+    when token == "true"    then true
+    when token == "false"   then false
+    when token == "nil"     then nil
+    when token[0] == '"'    then token[1..-2].gsub(/\\"/, "\"")
+    when token[0] == ':'    then "\u029e#{token[1..-1]}"
+    else                         Mal::Symbol.new token
+    end
+  end
+
+  def list_of(symname)
+    Mal::List.new << gen_type(Mal::Symbol, symname) << read_form
+  end
+
+  def read_form
+    token = peek
+
+    parse_error "unexpected EOF" unless token
+    parse_error "unexpected comment" if token[0] == ';'
+
+    Mal::Type.new case token
+    when "("  then read_list
+    when ")"  then parse_error "unexpected ')'"
+    when "["  then read_vector
+    when "]"  then parse_error "unexpected ']'"
+    when "{"  then read_hashmap
+    when "}"  then parse_error "unexpected '}'"
+    when "'"  then self.next; list_of("quote")
+    when "`"  then self.next; list_of("quasiquote")
+    when "~"  then self.next; list_of("unquote")
+    when "~@" then self.next; list_of("splice-unquote")
+    when "@"  then self.next; list_of("deref")
+    when "^"
+      self.next
+      meta = read_form
+      list_of("with-meta") << meta
+    else read_atom
+    end
+  end
+
+end
+
+def tokenize(str)
+  regex = /[\s,]*(~@|[\[\]{}()'`~^@]|"(?:\\.|[^\\"])*"|;.*|[^\s\[\]{}('"`,;)]*)/
+  str.scan(regex).map{|m| m[1]}.reject(&.empty?)
+end
+
+def read_str(str)
+  r = Reader.new(tokenize(str))
+  begin
+    r.read_form
+  ensure
+    unless r.peek.nil?
+      raise Mal::ParseException.new "expected EOF, got #{r.peek.to_s}"
+    end
+  end
+end
+
diff --git a/src/readline.cr b/src/readline.cr
new file mode 100644
index 0000000..e57099a
--- /dev/null
+++ b/src/readline.cr
@@ -0,0 +1,21 @@
+# Note:
+# Crystal already has "readline" library.
+# I implemented a subset of it again for practice.
+
+@[Link("readline")]
+lib LibReadline
+  fun readline(prompt : UInt8*) : UInt8*
+  fun add_history(line : UInt8*)
+end
+
+def my_readline(prompt = "")
+  line = LibReadline.readline(prompt)
+  if line
+    LibReadline.add_history(line)
+    String.new(line)
+  else
+    nil
+  end
+ensure
+  LibC.free(line as Void*) if line
+end
diff --git a/src/step0_repl.cr b/src/step0_repl.cr
new file mode 100755
index 0000000..e1fe58a
--- /dev/null
+++ b/src/step0_repl.cr
@@ -0,0 +1,26 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def read(x)
+    x
+end
+
+def eval(x)
+    x
+end
+
+def print(x)
+    x
+end
+
+def rep(x)
+    read(eval(print(x)))
+end
+
+while line = my_readline("user> ")
+    puts rep(line)
+end
diff --git a/src/step1_read_print.cr b/src/step1_read_print.cr
new file mode 100755
index 0000000..1f3896d
--- /dev/null
+++ b/src/step1_read_print.cr
@@ -0,0 +1,32 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+require "./reader"
+require "./printer"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def read(str)
+  read_str str
+end
+
+def eval(x)
+    x
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str)))
+end
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/step2_eval.cr b/src/step2_eval.cr
new file mode 100755
index 0000000..a9bf00d
--- /dev/null
+++ b/src/step2_eval.cr
@@ -0,0 +1,90 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+require "./reader"
+require "./printer"
+require "./types"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def eval_error(msg)
+  raise Mal::EvalException.new msg
+end
+
+def num_func(func)
+  -> (args : Array(Mal::Type)) {
+    x, y = args[0].unwrap, args[1].unwrap
+    eval_error "invalid arguments" unless x.is_a?(Int32) && y.is_a?(Int32)
+    Mal::Type.new func.call(x, y)
+  }
+end
+
+$repl_env = {
+  "+" => num_func(->(x : Int32, y : Int32){ x + y }),
+  "-" => num_func(->(x : Int32, y : Int32){ x - y }),
+  "*" => num_func(->(x : Int32, y : Int32){ x * y }),
+  "/" => num_func(->(x : Int32, y : Int32){ x / y }),
+} of String => Mal::Func
+
+def eval_ast(a, env)
+  return a.map{|n| eval(n, env) as Mal::Type} if a.is_a? Mal::List
+  return a unless a
+
+  ast = a.unwrap
+  case ast
+  when Mal::Symbol
+    if env.has_key? ast.str
+      env[ast.str]
+    else
+      eval_error "'#{ast.str}' not found"
+    end
+  when Mal::List
+    ast.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
+  when Mal::Vector
+    ast.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
+  when Mal::HashMap
+    ast.each{|k, v| ast[k] = eval(v, env)}
+  else
+    ast
+  end
+end
+
+def read(str)
+  read_str str
+end
+
+def eval(t, env)
+  Mal::Type.new case ast = t.unwrap
+  when Mal::List
+    eval_error "empty list" if ast.empty?
+
+    f = eval_ast(ast.first, env)
+    ast.shift(1)
+    args = eval_ast(ast, env)
+
+    if f.is_a?(Mal::Func)
+      f.call(args)
+    else
+      eval_error "expected function symbol as the first symbol of list"
+    end
+  else
+    eval_ast(t, env)
+  end
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str), $repl_env))
+end
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/step3_env.cr b/src/step3_env.cr
new file mode 100755
index 0000000..9c7fc99
--- /dev/null
+++ b/src/step3_env.cr
@@ -0,0 +1,115 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+require "./reader"
+require "./printer"
+require "./types"
+require "./env"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def eval_error(msg)
+  raise Mal::EvalException.new msg
+end
+
+def num_func(func)
+  -> (args : Array(Mal::Type)) {
+    x, y = args[0].unwrap, args[1].unwrap
+    eval_error "invalid arguments" unless x.is_a?(Int32) && y.is_a?(Int32)
+    Mal::Type.new func.call(x, y)
+  }
+end
+
+$repl_env = Mal::Env.new nil
+$repl_env.set("+", Mal::Type.new num_func(->(x : Int32, y : Int32){ x + y }))
+$repl_env.set("-", Mal::Type.new num_func(->(x : Int32, y : Int32){ x - y }))
+$repl_env.set("*", Mal::Type.new num_func(->(x : Int32, y : Int32){ x * y }))
+$repl_env.set("/", Mal::Type.new num_func(->(x : Int32, y : Int32){ x / y }))
+
+def eval_ast(a, env)
+  return a.map{|n| eval(n, env) } if a.is_a? Array
+
+  Mal::Type.new case ast = a.unwrap
+  when Mal::Symbol
+    if e = env.get(ast.str)
+      e
+    else
+      eval_error "'#{ast.str}' not found"
+    end
+  when Mal::List
+    ast.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
+  when Mal::Vector
+    ast.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
+  when Mal::HashMap
+    new_map = Mal::HashMap.new
+    ast.each{|k, v| new_map[k] = eval(v, env)}
+    new_map
+  else
+    ast
+  end
+end
+
+def read(str)
+  read_str str
+end
+
+def eval(t, env)
+  ast = t.unwrap
+
+  return eval_ast(t, env) unless ast.is_a?(Mal::List)
+
+  eval_error "empty list" if ast.empty?
+
+  sym = ast.first.unwrap
+  eval_error "first element of list must be a symbol" unless sym.is_a?(Mal::Symbol)
+
+  Mal::Type.new case sym.str
+  when "def!"
+    eval_error "wrong number of argument for 'def!'" unless ast.size == 3
+    a1 = ast[1].unwrap
+    eval_error "1st argument of 'def!' must be symbol" unless a1.is_a?(Mal::Symbol)
+    env.set(a1.str, eval(ast[2], env) as Mal::Type)
+  when "let*"
+    eval_error "wrong number of argument for 'def!'" unless ast.size == 3
+
+    bindings = ast[1].unwrap
+    eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a?(Array)
+    eval_error "size of binding list must be even" unless bindings.size.even?
+
+    new_env = Mal::Env.new env
+    bindings.each_slice(2) do |binding|
+      name, value = binding[0].unwrap, binding[1]
+      eval_error "name of binding must be specified as symbol" unless name.is_a?(Mal::Symbol)
+      new_env.set(name.str, eval(value, new_env))
+    end
+
+    eval(ast[2], new_env)
+  else
+    f = eval_ast(ast.first, env)
+    ast.shift(1)
+    args = eval_ast(ast, env)
+
+    if f.is_a?(Mal::Type) && (f2 = f.unwrap).is_a?(Mal::Func)
+      f2.call(args as Array(Mal::Type))
+    else
+      eval_error "expected function symbol as the first symbol of list"
+    end
+  end
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str), $repl_env))
+end
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/step4_if_fn_do.cr b/src/step4_if_fn_do.cr
new file mode 100755
index 0000000..3dc861c
--- /dev/null
+++ b/src/step4_if_fn_do.cr
@@ -0,0 +1,130 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+require "./reader"
+require "./printer"
+require "./types"
+require "./env"
+require "./core"
+require "./error"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def func_of(env, binds, body)
+  -> (args : Array(Mal::Type)) {
+    new_env = Mal::Env.new(env, binds, args)
+    eval(body, new_env)
+  } as Mal::Func
+end
+
+def eval_ast(ast, env)
+  return ast.map{|n| eval(n, env) as Mal::Type} if ast.is_a? Mal::List
+
+  val = ast.unwrap
+
+  Mal::Type.new case val
+  when Mal::Symbol
+    if e = env.get(val.str)
+      e
+    else
+      eval_error "'#{val.str}' not found"
+    end
+  when Mal::List
+    val.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
+  when Mal::Vector
+    val.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
+  when Mal::HashMap
+    val.each{|k, v| val[k] = eval(v, env)}
+    val
+  else
+    val
+  end
+end
+
+def eval_invocation(list, env)
+  f = eval(list.first, env).unwrap
+  eval_error "expected function symbol as the first symbol of list" unless f.is_a? Mal::Func
+  f.call eval_ast(list[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, env)
+end
+
+def read(str)
+  read_str str
+end
+
+def eval(ast, env)
+  list = ast.unwrap
+
+  return eval_ast(ast, env)          unless list.is_a? Mal::List
+  return gen_type Mal::List if list.empty?
+
+  head = list.first.unwrap
+
+  Mal::Type.new case head
+  when Mal::Symbol
+    case head.str
+    when "def!"
+      eval_error "wrong number of argument for 'def!'" unless list.size == 3
+      a1 = list[1].unwrap
+      eval_error "1st argument of 'def!' must be symbol" unless a1.is_a? Mal::Symbol
+      env.set(a1.str, eval(list[2], env))
+    when "let*"
+      eval_error "wrong number of argument for 'def!'" unless list.size == 3
+
+      bindings = list[1].unwrap
+      eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
+      eval_error "size of binding list must be even" unless bindings.size.even?
+
+      new_env = Mal::Env.new env
+      bindings.each_slice(2) do |binding|
+        key, value = binding
+        name = key.unwrap
+        eval_error "name of binding must be specified as symbol" unless name.is_a? Mal::Symbol
+        new_env.set(name.str, eval(value, new_env))
+      end
+
+      eval(list[2], new_env)
+    when "do"
+      list.shift 1
+      eval_ast(list, env).last
+    when "if"
+      cond = eval(list[1], env).unwrap
+      case cond
+      when Nil
+        list.size >= 4 ? eval(list[3], env) : nil
+      when false
+        list.size >= 4 ?  eval(list[3], env) : nil
+      else
+        eval(list[2], env)
+      end
+    when "fn*"
+      # Note:
+      # If writing lambda expression here directly, compiler will fail to infer type of 'list'. (Error 'Nil for empty?')
+      func_of(env, list[1].unwrap, list[2])
+    else
+      eval_invocation(list, env)
+    end
+  else
+    eval_invocation(list, env)
+  end
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str), $repl_env))
+end
+
+$repl_env = Mal::Env.new nil
+Mal::NS.each{|k,v| $repl_env.set(k, Mal::Type.new(v))}
+rep "(def! not (fn* (a) (if a false true)))"
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/step5_tco.cr b/src/step5_tco.cr
new file mode 100755
index 0000000..450e399
--- /dev/null
+++ b/src/step5_tco.cr
@@ -0,0 +1,164 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+require "./reader"
+require "./printer"
+require "./types"
+require "./env"
+require "./core"
+require "./error"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def func_of(env, binds, body)
+  -> (args : Array(Mal::Type)) {
+    new_env = Mal::Env.new(env, binds, args)
+    eval(body, new_env)
+  } as Mal::Func
+end
+
+def eval_ast(ast, env)
+  return ast.map{|n| eval(n, env) as Mal::Type} if ast.is_a? Mal::List
+
+  val = ast.unwrap
+
+  Mal::Type.new case val
+  when Mal::Symbol
+    if e = env.get(val.str)
+      e
+    else
+      eval_error "'#{val.str}' not found"
+    end
+  when Mal::List
+    val.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
+  when Mal::Vector
+    val.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
+  when Array(Mal::Type)
+    val.map{|n| eval(n, env)}
+  when Mal::HashMap
+    val.each{|k, v| val[k] = eval(v, env)}
+    val
+  else
+    val
+  end
+end
+
+def eval_invocation(list, env)
+  f = eval(list.first, env).unwrap
+  case f
+  when Mal::Closure
+    f.fn.call eval_ast(list[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, env)
+  when Mal::Func
+    f.call eval_ast(list[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, env)
+  else
+    eval_error "expected function as the first argument"
+  end
+end
+
+def read(str)
+  read_str str
+end
+
+macro invoke_list(l)
+  f = eval({{l}}.first, env).unwrap
+  args = eval_ast({{l}}[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, env)
+  case f
+  when Mal::Closure
+    ast = f.ast
+    env = Mal::Env.new(f.env, f.params, args)
+    next # TCO
+  when Mal::Func
+    return f.call args
+  else
+    eval_error "expected function as the first argument"
+  end
+end
+
+def eval(ast, env)
+  # 'next' in 'do...end' has a bug in crystal 0.7.1
+  # https://github.com/manastech/crystal/issues/659
+  while true
+    list = ast.unwrap
+
+    return eval_ast(ast, env) unless list.is_a? Mal::List
+    return gen_type Mal::List if list.empty?
+
+    head = list.first.unwrap
+
+    unless head.is_a? Mal::Symbol
+      invoke_list list
+    end
+
+    return Mal::Type.new case head.str
+      when "def!"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+        a1 = list[1].unwrap
+        eval_error "1st argument of 'def!' must be symbol" unless a1.is_a? Mal::Symbol
+        env.set(a1.str, eval(list[2], env))
+      when "let*"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+
+        bindings = list[1].unwrap
+        eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
+        eval_error "size of binding list must be even" unless bindings.size.even?
+
+        new_env = Mal::Env.new env
+        bindings.each_slice(2) do |binding|
+          key, value = binding
+          name = key.unwrap
+          eval_error "name of binding must be specified as symbol" unless name.is_a? Mal::Symbol
+          new_env.set(name.str, eval(value, new_env))
+        end
+
+        ast, env = list[2], new_env
+        next # TCO
+      when "do"
+        if list.empty?
+          ast = Mal::Type.new nil
+          next
+        end
+
+        eval_ast(list[1..-2].each_with_object(Mal::List.new){|i,l| l << i}, env)
+        ast = list.last
+        next # TCO
+      when "if"
+        ast = unless eval(list[1], env).unwrap
+          list.size >= 4 ? list[3] : Mal::Type.new(nil)
+        else
+          list[2]
+        end
+        next # TCO
+      when "fn*"
+        # Note:
+        # If writing lambda expression here directly, compiler will fail to infer type of 'list'. (Error 'Nil for empty?')
+        params = list[1].unwrap
+        unless params.is_a?(Mal::List) || params.is_a?(Mal::Vector)
+          eval_error "'fn*' parameters must be list"
+        end
+        Mal::Closure.new(list[2], params, env, func_of(env, list[1].unwrap, list[2]))
+      else
+        invoke_list list
+      end
+  end
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str), $repl_env))
+end
+
+$repl_env = Mal::Env.new nil
+Mal::NS.each{|k,v| $repl_env.set(k, Mal::Type.new(v))}
+rep "(def! not (fn* (a) (if a false true)))"
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/step6_file.cr b/src/step6_file.cr
new file mode 100755
index 0000000..1ffe493
--- /dev/null
+++ b/src/step6_file.cr
@@ -0,0 +1,177 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+require "./reader"
+require "./printer"
+require "./types"
+require "./env"
+require "./core"
+require "./error"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def func_of(env, binds, body)
+  -> (args : Array(Mal::Type)) {
+    new_env = Mal::Env.new(env, binds, args)
+    eval(body, new_env)
+  } as Mal::Func
+end
+
+def eval_ast(ast, env)
+  return ast.map{|n| eval(n, env) as Mal::Type} if ast.is_a? Mal::List
+
+  val = ast.unwrap
+
+  Mal::Type.new case val
+  when Mal::Symbol
+    if e = env.get(val.str)
+      e
+    else
+      eval_error "'#{val.str}' not found"
+    end
+  when Mal::List
+    val.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
+  when Mal::Vector
+    val.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
+  when Array(Mal::Type)
+    val.map{|n| eval(n, env)}
+  when Mal::HashMap
+    val.each{|k, v| val[k] = eval(v, env)}
+    val
+  else
+    val
+  end
+end
+
+def eval_invocation(list, env)
+  f = eval(list.first, env).unwrap
+  case f
+  when Mal::Closure
+    f.fn.call eval_ast(list[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, env)
+  when Mal::Func
+    f.call eval_ast(list[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, env)
+  else
+    eval_error "expected function as the first argument"
+  end
+end
+
+def read(str)
+  read_str str
+end
+
+macro invoke_list(l, env)
+  f = eval({{l}}.first, {{env}}).unwrap
+  args = eval_ast({{l}}[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, {{env}})
+  case f
+  when Mal::Closure
+    ast = f.ast
+    {{env}} = Mal::Env.new(f.env, f.params, args)
+    next # TCO
+  when Mal::Func
+    return f.call args
+  else
+    eval_error "expected function as the first argument"
+  end
+end
+
+def eval(ast, env)
+  # 'next' in 'do...end' has a bug in crystal 0.7.1
+  # https://github.com/manastech/crystal/issues/659
+  while true
+    list = ast.unwrap
+
+    return eval_ast(ast, env) unless list.is_a? Mal::List
+    return gen_type Mal::List if list.empty?
+
+    head = list.first.unwrap
+
+    unless head.is_a? Mal::Symbol
+      invoke_list(list, env)
+    end
+
+    return Mal::Type.new case head.str
+      when "def!"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+        a1 = list[1].unwrap
+        eval_error "1st argument of 'def!' must be symbol" unless a1.is_a? Mal::Symbol
+        env.set(a1.str, eval(list[2], env))
+      when "let*"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+
+        bindings = list[1].unwrap
+        eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
+        eval_error "size of binding list must be even" unless bindings.size.even?
+
+        new_env = Mal::Env.new env
+        bindings.each_slice(2) do |binding|
+          key, value = binding
+          name = key.unwrap
+          eval_error "name of binding must be specified as symbol" unless name.is_a? Mal::Symbol
+          new_env.set(name.str, eval(value, new_env))
+        end
+
+        ast, env = list[2], new_env
+        next # TCO
+      when "do"
+        if list.empty?
+          ast = Mal::Type.new nil
+          next
+        end
+
+        eval_ast(list[1..-2].each_with_object(Mal::List.new){|i,l| l << i}, env)
+        ast = list.last
+        next # TCO
+      when "if"
+        ast = unless eval(list[1], env).unwrap
+          list.size >= 4 ? list[3] : Mal::Type.new(nil)
+        else
+          list[2]
+        end
+        next # TCO
+      when "fn*"
+        params = list[1].unwrap
+        unless params.is_a?(Mal::List) || params.is_a?(Mal::Vector)
+          eval_error "'fn*' parameters must be list"
+        end
+        Mal::Closure.new(list[2], params, env, func_of(env, params, list[2]))
+      else
+        invoke_list(list, env)
+      end
+  end
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str), $repl_env))
+end
+
+$repl_env = Mal::Env.new nil
+Mal::NS.each{|k,v| $repl_env.set(k, Mal::Type.new(v))}
+$repl_env.set("eval", Mal::Type.new -> (args: Array(Mal::Type)){ eval(args[0], $repl_env) })
+rep "(def! not (fn* (a) (if a false true)))"
+rep "(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))"
+$argv = Mal::List.new
+$repl_env.set("*ARGV*", Mal::Type.new $argv)
+
+unless ARGV.empty?
+  if ARGV.size > 1
+    ARGV[1..-1].each do |a|
+      $argv << Mal::Type.new(a)
+    end
+  end
+
+  rep "(load-file \"#{ARGV[0]}\")"
+  exit
+end
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/step7_quote.cr b/src/step7_quote.cr
new file mode 100755
index 0000000..2c43818
--- /dev/null
+++ b/src/step7_quote.cr
@@ -0,0 +1,207 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+require "./reader"
+require "./printer"
+require "./types"
+require "./env"
+require "./core"
+require "./error"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def func_of(env, binds, body)
+  -> (args : Array(Mal::Type)) {
+    new_env = Mal::Env.new(env, binds, args)
+    eval(body, new_env)
+  } as Mal::Func
+end
+
+def eval_ast(ast, env)
+  return ast.map{|n| eval(n, env) as Mal::Type} if ast.is_a? Mal::List
+
+  val = ast.unwrap
+
+  Mal::Type.new case val
+  when Mal::Symbol
+    if e = env.get(val.str)
+      e
+    else
+      eval_error "'#{val.str}' not found"
+    end
+  when Mal::List
+    val.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
+  when Mal::Vector
+    val.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
+  when Array(Mal::Type)
+    val.map{|n| eval(n, env)}
+  when Mal::HashMap
+    val.each{|k, v| val[k] = eval(v, env)}
+    val
+  else
+    val
+  end
+end
+
+def read(str)
+  read_str str
+end
+
+macro is_pair(list)
+  {{list}}.is_a?(Array) && !{{list}}.empty?
+end
+
+def quasiquote(ast)
+  list = ast.unwrap
+
+  unless is_pair(list)
+    return Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "quote") << ast
+    )
+  end
+
+  head = list.first.unwrap
+
+  case
+  # ("unquote" ...)
+  when head.is_a?(Mal::Symbol) && head.str == "unquote"
+    list[1]
+  # (("splice-unquote" ...) ...)
+  when is_pair(head) && (arg0 = head.first.unwrap).is_a?(Mal::Symbol) && arg0.str == "splice-unquote"
+    tail = Mal::Type.new list[1..-1].each_with_object(Mal::List.new){|e,l| l << e}
+    Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "concat") << head[1] << quasiquote(tail)
+    )
+  else
+    tail = Mal::Type.new list[1..-1].each_with_object(Mal::List.new){|e,l| l << e}
+    Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "cons") << quasiquote(list.first) << quasiquote(tail)
+    )
+  end
+end
+
+macro invoke_list(l, env)
+  f = eval({{l}}.first, {{env}}).unwrap
+  args = eval_ast({{l}}[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, {{env}})
+  case f
+  when Mal::Closure
+    ast = f.ast
+    {{env}} = Mal::Env.new(f.env, f.params, args)
+    next # TCO
+  when Mal::Func
+    return f.call args
+  else
+    eval_error "expected function as the first argument"
+  end
+end
+
+def eval(ast, env)
+  # 'next' in 'do...end' has a bug in crystal 0.7.1
+  # https://github.com/manastech/crystal/issues/659
+  while true
+    list = ast.unwrap
+
+    return eval_ast(ast, env) unless list.is_a? Mal::List
+    return gen_type Mal::List if list.empty?
+
+    head = list.first.unwrap
+
+    unless head.is_a? Mal::Symbol
+      return invoke_list(list, env)
+    end
+
+    return Mal::Type.new case head.str
+      when "def!"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+        a1 = list[1].unwrap
+        eval_error "1st argument of 'def!' must be symbol" unless a1.is_a? Mal::Symbol
+        env.set(a1.str, eval(list[2], env))
+      when "let*"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+
+        bindings = list[1].unwrap
+        eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
+        eval_error "size of binding list must be even" unless bindings.size.even?
+
+        new_env = Mal::Env.new env
+        bindings.each_slice(2) do |binding|
+          key, value = binding
+          name = key.unwrap
+          eval_error "name of binding must be specified as symbol" unless name.is_a? Mal::Symbol
+          new_env.set(name.str, eval(value, new_env))
+        end
+
+        ast, env = list[2], new_env
+        next # TCO
+      when "do"
+        if list.empty?
+          ast = Mal::Type.new nil
+          next
+        end
+
+        eval_ast(list[1..-2].each_with_object(Mal::List.new){|i,l| l << i}, env)
+        ast = list.last
+        next # TCO
+      when "if"
+        ast = unless eval(list[1], env).unwrap
+          list.size >= 4 ? list[3] : Mal::Type.new(nil)
+        else
+          list[2]
+        end
+        next # TCO
+      when "fn*"
+        params = list[1].unwrap
+        unless params.is_a?(Mal::List) || params.is_a?(Mal::Vector)
+          eval_error "'fn*' parameters must be list"
+        end
+        Mal::Closure.new(list[2], params, env, func_of(env, params, list[2]))
+      when "quote"
+        list[1]
+      when "quasiquote"
+        ast = quasiquote list[1]
+        next # TCO
+      else
+        invoke_list(list, env)
+      end
+  end
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str), $repl_env))
+end
+
+$repl_env = Mal::Env.new nil
+Mal::NS.each{|k,v| $repl_env.set(k, Mal::Type.new(v))}
+$repl_env.set("eval", Mal::Type.new -> (args: Array(Mal::Type)){ eval(args[0], $repl_env) })
+rep "(def! not (fn* (a) (if a false true)))"
+rep "(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))"
+$argv = Mal::List.new
+$repl_env.set("*ARGV*", Mal::Type.new $argv)
+
+unless ARGV.empty?
+  if ARGV.size > 1
+    ARGV[1..-1].each do |a|
+      $argv << Mal::Type.new(a)
+    end
+  end
+
+  begin
+    rep "(load-file \"#{ARGV[0]}\")"
+  rescue e
+    STDERR.puts e
+  end
+  exit
+end
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/step8_macros.cr b/src/step8_macros.cr
new file mode 100755
index 0000000..73f1470
--- /dev/null
+++ b/src/step8_macros.cr
@@ -0,0 +1,253 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+require "./reader"
+require "./printer"
+require "./types"
+require "./env"
+require "./core"
+require "./error"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def func_of(env, binds, body)
+  -> (args : Array(Mal::Type)) {
+    new_env = Mal::Env.new(env, binds, args)
+    eval(body, new_env)
+  } as Mal::Func
+end
+
+def eval_ast(ast, env)
+  return ast.map{|n| eval(n, env) as Mal::Type} if ast.is_a? Mal::List
+
+  val = ast.unwrap
+
+  Mal::Type.new case val
+  when Mal::Symbol
+    if e = env.get(val.str)
+      e
+    else
+      eval_error "'#{val.str}' not found"
+    end
+  when Mal::List
+    val.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
+  when Mal::Vector
+    val.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
+  when Array(Mal::Type)
+    val.map{|n| eval(n, env)}
+  when Mal::HashMap
+    val.each{|k, v| val[k] = eval(v, env)}
+    val
+  else
+    val
+  end
+end
+
+def read(str)
+  read_str str
+end
+
+macro pair?(list)
+  {{list}}.is_a?(Array) && !{{list}}.empty?
+end
+
+def quasiquote(ast)
+  list = ast.unwrap
+
+  unless pair?(list)
+    return Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "quote") << ast
+    )
+  end
+
+  head = list.first.unwrap
+
+  case
+  # ("unquote" ...)
+  when head.is_a?(Mal::Symbol) && head.str == "unquote"
+    list[1]
+  # (("splice-unquote" ...) ...)
+  when pair?(head) && (arg0 = head.first.unwrap).is_a?(Mal::Symbol) && arg0.str == "splice-unquote"
+    tail = Mal::Type.new list[1..-1].each_with_object(Mal::List.new){|e,l| l << e}
+    Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "concat") << head[1] << quasiquote(tail)
+    )
+  else
+    tail = Mal::Type.new list[1..-1].each_with_object(Mal::List.new){|e,l| l << e}
+    Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "cons") << quasiquote(list.first) << quasiquote(tail)
+    )
+  end
+end
+
+def macro_call?(ast, env)
+  list = ast.unwrap
+  return false unless list.is_a? Mal::List
+
+  sym = list.first.unwrap
+  return false unless sym.is_a? Mal::Symbol
+
+  func = env.find(sym.str).try(&.data[sym.str])
+  return false unless func && func.macro?
+
+  true
+end
+
+def macroexpand(ast, env)
+  while macro_call?(ast, env)
+
+    # Already checked in macro_call?
+    list = ast.unwrap as Mal::List
+    func_sym = list[0].unwrap as Mal::Symbol
+    func = env.get(func_sym.str).unwrap
+
+    case func
+    when Mal::Func
+      ast = func.call(list[1..-1])
+    when Mal::Closure
+      ast = func.fn.call(list[1..-1])
+    else
+      eval_error "macro '#{func_sym.str}' must be function: #{ast}"
+    end
+  end
+
+  ast
+end
+
+macro invoke_list(l, env)
+  f = eval({{l}}.first, {{env}}).unwrap
+  args = eval_ast({{l}}[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, {{env}})
+  case f
+  when Mal::Closure
+    ast = f.ast
+    {{env}} = Mal::Env.new(f.env, f.params, args)
+    next # TCO
+  when Mal::Func
+    return f.call args
+  else
+    eval_error "expected function as the first argument: #{f}"
+  end
+end
+
+def eval(ast, env)
+  # 'next' in 'do...end' has a bug in crystal 0.7.1
+  # https://github.com/manastech/crystal/issues/659
+  while true
+    return eval_ast(ast, env) unless ast.unwrap.is_a? Mal::List
+
+    ast = macroexpand(ast, env)
+
+    list = ast.unwrap
+
+    return ast unless list.is_a? Mal::List
+    return ast if list.empty?
+
+    head = list.first.unwrap
+
+    return invoke_list(list, env) unless head.is_a? Mal::Symbol
+
+    return Mal::Type.new case head.str
+      when "def!"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+        a1 = list[1].unwrap
+        eval_error "1st argument of 'def!' must be symbol: #{a1}" unless a1.is_a? Mal::Symbol
+        env.set(a1.str, eval(list[2], env))
+      when "let*"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+
+        bindings = list[1].unwrap
+        eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
+        eval_error "size of binding list must be even" unless bindings.size.even?
+
+        new_env = Mal::Env.new env
+        bindings.each_slice(2) do |binding|
+          key, value = binding
+          name = key.unwrap
+          eval_error "name of binding must be specified as symbol #{name}" unless name.is_a? Mal::Symbol
+          new_env.set(name.str, eval(value, new_env))
+        end
+
+        ast, env = list[2], new_env
+        next # TCO
+      when "do"
+        if list.empty?
+          ast = Mal::Type.new nil
+          next
+        end
+
+        eval_ast(list[1..-2].each_with_object(Mal::List.new){|i,l| l << i}, env)
+        ast = list.last
+        next # TCO
+      when "if"
+        ast = unless eval(list[1], env).unwrap
+          list.size >= 4 ? list[3] : Mal::Type.new(nil)
+        else
+          list[2]
+        end
+        next # TCO
+      when "fn*"
+        params = list[1].unwrap
+        unless params.is_a? Array
+          eval_error "'fn*' parameters must be list or vector: #{params}"
+        end
+        Mal::Closure.new(list[2], params, env, func_of(env, params, list[2]))
+      when "quote"
+        list[1]
+      when "quasiquote"
+        ast = quasiquote list[1]
+        next # TCO
+      when "defmacro!"
+        eval_error "wrong number of argument for 'defmacro!'" unless list.size == 3
+        a1 = list[1].unwrap
+        eval_error "1st argument of 'defmacro!' must be symbol: #{a1}" unless a1.is_a? Mal::Symbol
+        env.set(a1.str, eval(list[2], env).tap{|n| n.is_macro = true})
+      when "macroexpand"
+        macroexpand(list[1], env)
+      else
+        invoke_list(list, env)
+      end
+  end
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str), $repl_env))
+end
+
+$repl_env = Mal::Env.new nil
+Mal::NS.each{|k,v| $repl_env.set(k, Mal::Type.new(v))}
+$repl_env.set("eval", Mal::Type.new -> (args: Array(Mal::Type)){ eval(args[0], $repl_env) })
+rep "(def! not (fn* (a) (if a false true)))"
+rep "(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))"
+rep "(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw \"odd number of forms to cond\")) (cons 'cond (rest (rest xs)))))))"
+rep "(defmacro! or (fn* (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs) `(let* (or_FIXME ~(first xs)) (if or_FIXME or_FIXME (or ~@(rest xs))))))))"
+
+$argv = Mal::List.new
+$repl_env.set("*ARGV*", Mal::Type.new $argv)
+
+unless ARGV.empty?
+  if ARGV.size > 1
+    ARGV[1..-1].each do |a|
+      $argv << Mal::Type.new(a)
+    end
+  end
+
+  begin
+    rep "(load-file \"#{ARGV[0]}\")"
+  rescue e
+    STDERR.puts e
+  end
+  exit
+end
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/step9_try.cr b/src/step9_try.cr
new file mode 100755
index 0000000..3d2c964
--- /dev/null
+++ b/src/step9_try.cr
@@ -0,0 +1,270 @@
+#! /usr/bin/env crystal run
+
+require "./readline"
+require "./reader"
+require "./printer"
+require "./types"
+require "./env"
+require "./core"
+require "./error"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def func_of(env, binds, body)
+  -> (args : Array(Mal::Type)) {
+    new_env = Mal::Env.new(env, binds, args)
+    eval(body, new_env)
+  } as Mal::Func
+end
+
+def eval_ast(ast, env)
+  return ast.map{|n| eval(n, env) as Mal::Type} if ast.is_a? Mal::List
+
+  val = ast.unwrap
+
+  Mal::Type.new case val
+  when Mal::Symbol
+    if e = env.get(val.str)
+      e
+    else
+      eval_error "'#{val.str}' not found"
+    end
+  when Mal::List
+    val.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
+  when Mal::Vector
+    val.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
+  when Array(Mal::Type)
+    val.map{|n| eval(n, env)}
+  when Mal::HashMap
+    val.each{|k, v| val[k] = eval(v, env)}
+    val
+  else
+    val
+  end
+end
+
+def read(str)
+  read_str str
+end
+
+macro pair?(list)
+  {{list}}.is_a?(Array) && !{{list}}.empty?
+end
+
+def quasiquote(ast)
+  list = ast.unwrap
+
+  unless pair?(list)
+    return Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "quote") << ast
+    )
+  end
+
+  head = list.first.unwrap
+
+  case
+  # ("unquote" ...)
+  when head.is_a?(Mal::Symbol) && head.str == "unquote"
+    list[1]
+  # (("splice-unquote" ...) ...)
+  when pair?(head) && (arg0 = head.first.unwrap).is_a?(Mal::Symbol) && arg0.str == "splice-unquote"
+    tail = Mal::Type.new list[1..-1].to_mal
+    Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "concat") << head[1] << quasiquote(tail)
+    )
+  else
+    tail = Mal::Type.new list[1..-1].to_mal
+    Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "cons") << quasiquote(list.first) << quasiquote(tail)
+    )
+  end
+end
+
+def macro_call?(ast, env)
+  list = ast.unwrap
+  return false unless list.is_a? Mal::List
+
+  sym = list.first.unwrap
+  return false unless sym.is_a? Mal::Symbol
+
+  func = env.find(sym.str).try(&.data[sym.str])
+  return false unless func && func.macro?
+
+  true
+end
+
+def macroexpand(ast, env)
+  while macro_call?(ast, env)
+
+    # Already checked in macro_call?
+    list = ast.unwrap as Mal::List
+    func_sym = list[0].unwrap as Mal::Symbol
+    func = env.get(func_sym.str).unwrap
+
+    case func
+    when Mal::Func
+      ast = func.call(list[1..-1])
+    when Mal::Closure
+      ast = func.fn.call(list[1..-1])
+    else
+      eval_error "macro '#{func_sym.str}' must be function: #{ast}"
+    end
+  end
+
+  ast
+end
+
+macro invoke_list(l, env)
+  f = eval({{l}}.first, {{env}}).unwrap
+  args = eval_ast({{l}}[1..-1].to_mal, {{env}})
+  case f
+  when Mal::Closure
+    ast = f.ast
+    {{env}} = Mal::Env.new(f.env, f.params, args)
+    next # TCO
+  when Mal::Func
+    return f.call args
+  else
+    eval_error "expected function as the first argument: #{f}"
+  end
+end
+
+def eval(ast, env)
+  # 'next' in 'do...end' has a bug in crystal 0.7.1
+  # https://github.com/manastech/crystal/issues/659
+  while true
+    return eval_ast(ast, env) unless ast.unwrap.is_a? Mal::List
+
+    ast = macroexpand(ast, env)
+
+    list = ast.unwrap
+
+    return ast unless list.is_a? Mal::List
+    return ast if list.empty?
+
+    head = list.first.unwrap
+
+    return invoke_list(list, env) unless head.is_a? Mal::Symbol
+
+    return Mal::Type.new case head.str
+      when "def!"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+        a1 = list[1].unwrap
+        eval_error "1st argument of 'def!' must be symbol: #{a1}" unless a1.is_a? Mal::Symbol
+        env.set(a1.str, eval(list[2], env))
+      when "let*"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+
+        bindings = list[1].unwrap
+        eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
+        eval_error "size of binding list must be even" unless bindings.size.even?
+
+        new_env = Mal::Env.new env
+        bindings.each_slice(2) do |binding|
+          key, value = binding
+          name = key.unwrap
+          eval_error "name of binding must be specified as symbol #{name}" unless name.is_a? Mal::Symbol
+          new_env.set(name.str, eval(value, new_env))
+        end
+
+        ast, env = list[2], new_env
+        next # TCO
+      when "do"
+        if list.empty?
+          ast = Mal::Type.new nil
+          next
+        end
+
+        eval_ast(list[1..-2].to_mal, env)
+        ast = list.last
+        next # TCO
+      when "if"
+        ast = unless eval(list[1], env).unwrap
+          list.size >= 4 ? list[3] : Mal::Type.new(nil)
+        else
+          list[2]
+        end
+        next # TCO
+      when "fn*"
+        params = list[1].unwrap
+        unless params.is_a? Array
+          eval_error "'fn*' parameters must be list or vector: #{params}"
+        end
+        Mal::Closure.new(list[2], params, env, func_of(env, params, list[2]))
+      when "quote"
+        list[1]
+      when "quasiquote"
+        ast = quasiquote list[1]
+        next # TCO
+      when "defmacro!"
+        eval_error "wrong number of argument for 'defmacro!'" unless list.size == 3
+        a1 = list[1].unwrap
+        eval_error "1st argument of 'defmacro!' must be symbol: #{a1}" unless a1.is_a? Mal::Symbol
+        env.set(a1.str, eval(list[2], env).tap{|n| n.is_macro = true})
+      when "macroexpand"
+        macroexpand(list[1], env)
+      when "try*"
+        catch_list = list[2].unwrap
+        return eval(list[1], env) unless catch_list.is_a? Mal::List
+
+        catch_head = catch_list.first.unwrap
+        return eval(list[1], env) unless catch_head.is_a? Mal::Symbol
+        return eval(list[1], env) unless catch_head.str == "catch*"
+
+        begin
+          eval(list[1], env)
+        rescue e : Mal::RuntimeException
+          new_env = Mal::Env.new(env, [catch_list[1]], [e.thrown])
+          eval(catch_list[2], new_env)
+        rescue e
+          new_env = Mal::Env.new(env, [catch_list[1]], [Mal::Type.new e.message])
+          eval(catch_list[2], new_env)
+        end
+      else
+        invoke_list(list, env)
+      end
+  end
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str), $repl_env))
+end
+
+$repl_env = Mal::Env.new nil
+Mal::NS.each{|k,v| $repl_env.set(k, Mal::Type.new(v))}
+$repl_env.set("eval", Mal::Type.new -> (args: Array(Mal::Type)){ eval(args[0], $repl_env) })
+rep "(def! not (fn* (a) (if a false true)))"
+rep "(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))"
+rep "(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw \"odd number of forms to cond\")) (cons 'cond (rest (rest xs)))))))"
+rep "(defmacro! or (fn* (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs) `(let* (or_FIXME ~(first xs)) (if or_FIXME or_FIXME (or ~@(rest xs))))))))"
+
+$argv = Mal::List.new
+$repl_env.set("*ARGV*", Mal::Type.new $argv)
+
+unless ARGV.empty?
+  if ARGV.size > 1
+    ARGV[1..-1].each do |a|
+      $argv << Mal::Type.new(a)
+    end
+  end
+
+  begin
+    rep "(load-file \"#{ARGV[0]}\")"
+  rescue e
+    STDERR.puts e
+  end
+  exit
+end
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/stepA_mal.cr b/src/stepA_mal.cr
new file mode 100755
index 0000000..49361ef
--- /dev/null
+++ b/src/stepA_mal.cr
@@ -0,0 +1,280 @@
+#! /usr/bin/env crystal run
+
+require "colorize"
+
+require "./readline"
+require "./reader"
+require "./printer"
+require "./types"
+require "./env"
+require "./core"
+require "./error"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+def func_of(env, binds, body)
+  -> (args : Array(Mal::Type)) {
+    new_env = Mal::Env.new(env, binds, args)
+    eval(body, new_env)
+  } as Mal::Func
+end
+
+def eval_ast(ast, env)
+  return ast.map{|n| eval(n, env) as Mal::Type} if ast.is_a? Array
+
+  val = ast.unwrap
+
+  Mal::Type.new case val
+  when Mal::Symbol
+    if e = env.get(val.str)
+      e
+    else
+      eval_error "'#{val.str}' not found"
+    end
+  when Mal::List
+    val.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
+  when Mal::Vector
+    val.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
+  when Mal::HashMap
+    new_map = Mal::HashMap.new
+    val.each{|k, v| new_map[k] = eval(v, env)}
+    new_map
+  else
+    val
+  end
+end
+
+def read(str)
+  read_str str
+end
+
+macro pair?(list)
+  {{list}}.is_a?(Array) && !{{list}}.empty?
+end
+
+def quasiquote(ast)
+  list = ast.unwrap
+
+  unless pair?(list)
+    return Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "quote") << ast
+    )
+  end
+
+  head = list.first.unwrap
+
+  case
+  # ("unquote" ...)
+  when head.is_a?(Mal::Symbol) && head.str == "unquote"
+    list[1]
+  # (("splice-unquote" ...) ...)
+  when pair?(head) && (arg0 = head.first.unwrap).is_a?(Mal::Symbol) && arg0.str == "splice-unquote"
+    tail = Mal::Type.new list[1..-1].to_mal
+    Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "concat") << head[1] << quasiquote(tail)
+    )
+  else
+    tail = Mal::Type.new list[1..-1].to_mal
+    Mal::Type.new(
+      Mal::List.new << gen_type(Mal::Symbol, "cons") << quasiquote(list.first) << quasiquote(tail)
+    )
+  end
+end
+
+def macro_call?(ast, env)
+  list = ast.unwrap
+  return false unless list.is_a? Mal::List
+  return false if list.empty?
+
+  sym = list.first.unwrap
+  return false unless sym.is_a? Mal::Symbol
+
+  func = env.find(sym.str).try(&.data[sym.str])
+  return false unless func && func.macro?
+
+  true
+end
+
+def macroexpand(ast, env)
+  while macro_call?(ast, env)
+
+    # Already checked in macro_call?
+    list = ast.unwrap as Mal::List
+    func_sym = list[0].unwrap as Mal::Symbol
+    func = env.get(func_sym.str).unwrap
+
+    case func
+    when Mal::Func
+      ast = func.call(list[1..-1])
+    when Mal::Closure
+      ast = func.fn.call(list[1..-1])
+    else
+      eval_error "macro '#{func_sym.str}' must be function: #{ast}"
+    end
+  end
+
+  ast
+end
+
+macro invoke_list(l, env)
+  f = eval({{l}}.first, {{env}}).unwrap
+  args = eval_ast({{l}}[1..-1], {{env}}) as Array
+
+  case f
+  when Mal::Closure
+    ast = f.ast
+    {{env}} = Mal::Env.new(f.env, f.params, args)
+    next # TCO
+  when Mal::Func
+    return f.call args
+  else
+    eval_error "expected function as the first argument: #{f}"
+  end
+end
+
+def debug(ast)
+  puts print(ast).colorize.red
+end
+
+def eval(ast, env)
+  # 'next' in 'do...end' has a bug in crystal 0.7.1
+  # https://github.com/manastech/crystal/issues/659
+  while true
+    return eval_ast(ast, env) unless ast.unwrap.is_a? Mal::List
+
+    ast = macroexpand(ast, env)
+
+    list = ast.unwrap
+
+    return ast unless list.is_a? Mal::List
+    return ast if list.empty?
+
+    head = list.first.unwrap
+
+    return invoke_list(list, env) unless head.is_a? Mal::Symbol
+
+    return Mal::Type.new case head.str
+      when "def!"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+        a1 = list[1].unwrap
+        eval_error "1st argument of 'def!' must be symbol: #{a1}" unless a1.is_a? Mal::Symbol
+        env.set(a1.str, eval(list[2], env))
+      when "let*"
+        eval_error "wrong number of argument for 'def!'" unless list.size == 3
+
+        bindings = list[1].unwrap
+        eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
+        eval_error "size of binding list must be even" unless bindings.size.even?
+
+        new_env = Mal::Env.new env
+        bindings.each_slice(2) do |binding|
+          key, value = binding
+          name = key.unwrap
+          eval_error "name of binding must be specified as symbol #{name}" unless name.is_a? Mal::Symbol
+          new_env.set(name.str, eval(value, new_env))
+        end
+
+        ast, env = list[2], new_env
+        next # TCO
+      when "do"
+        if list.empty?
+          ast = Mal::Type.new nil
+          next
+        end
+
+        eval_ast(list[1..-2].to_mal, env)
+        ast = list.last
+        next # TCO
+      when "if"
+        ast = unless eval(list[1], env).unwrap
+          list.size >= 4 ? list[3] : Mal::Type.new(nil)
+        else
+          list[2]
+        end
+        next # TCO
+      when "fn*"
+        params = list[1].unwrap
+        unless params.is_a? Array
+          eval_error "'fn*' parameters must be list or vector: #{params}"
+        end
+        Mal::Closure.new(list[2], params, env, func_of(env, params, list[2]))
+      when "quote"
+        list[1]
+      when "quasiquote"
+        ast = quasiquote list[1]
+        next # TCO
+      when "defmacro!"
+        eval_error "wrong number of argument for 'defmacro!'" unless list.size == 3
+        a1 = list[1].unwrap
+        eval_error "1st argument of 'defmacro!' must be symbol: #{a1}" unless a1.is_a? Mal::Symbol
+        env.set(a1.str, eval(list[2], env).tap{|n| n.is_macro = true})
+      when "macroexpand"
+        macroexpand(list[1], env)
+      when "try*"
+        catch_list = list[2].unwrap
+        return eval(list[1], env) unless catch_list.is_a? Mal::List
+
+        catch_head = catch_list.first.unwrap
+        return eval(list[1], env) unless catch_head.is_a? Mal::Symbol
+        return eval(list[1], env) unless catch_head.str == "catch*"
+
+        begin
+          eval(list[1], env)
+        rescue e : Mal::RuntimeException
+          new_env = Mal::Env.new(env, [catch_list[1]], [e.thrown])
+          eval(catch_list[2], new_env)
+        rescue e
+          new_env = Mal::Env.new(env, [catch_list[1]], [Mal::Type.new e.message])
+          eval(catch_list[2], new_env)
+        end
+      else
+        invoke_list(list, env)
+      end
+  end
+end
+
+def print(result)
+  pr_str(result, true)
+end
+
+def rep(str)
+  print(eval(read(str), $repl_env))
+end
+
+$repl_env = Mal::Env.new nil
+Mal::NS.each{|k,v| $repl_env.set(k, Mal::Type.new(v))}
+$repl_env.set("eval", Mal::Type.new -> (args: Array(Mal::Type)){ eval(args[0], $repl_env) })
+rep "(def! not (fn* (a) (if a false true)))"
+rep "(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))"
+rep "(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw \"odd number of forms to cond\")) (cons 'cond (rest (rest xs)))))))"
+rep "(defmacro! or (fn* (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs) `(let* (or_FIXME ~(first xs)) (if or_FIXME or_FIXME (or ~@(rest xs))))))))"
+rep("(def! *host-language* \"crystal\")")
+
+$argv = Mal::List.new
+$repl_env.set("*ARGV*", Mal::Type.new $argv)
+
+unless ARGV.empty?
+  if ARGV.size > 1
+    ARGV[1..-1].each do |a|
+      $argv << Mal::Type.new(a)
+    end
+  end
+
+  begin
+    rep "(load-file \"#{ARGV[0]}\")"
+  rescue e
+    STDERR.puts e
+  end
+  exit
+end
+
+rep("(println (str \"Mal [\" *host-language* \"]\"))")
+
+while line = my_readline("user> ")
+  begin
+    puts rep(line)
+  rescue e
+    STDERR.puts e
+  end
+end
diff --git a/src/types.cr b/src/types.cr
new file mode 100644
index 0000000..af61cb7
--- /dev/null
+++ b/src/types.cr
@@ -0,0 +1,114 @@
+require "./printer"
+
+module Mal
+  class Symbol
+    property :str
+    def initialize(@str)
+    end
+
+    def ==(other : Symbol)
+      @str == other.str
+    end
+  end
+
+  class List < Array(Type)
+  end
+
+  class Vector < Array(Type)
+  end
+
+  class HashMap < Hash(String, Type)
+  end
+
+  class Atom
+    property :val
+    def initialize(@val)
+    end
+
+    def ==(rhs : Atom)
+      @val == rhs.val
+    end
+  end
+
+  class Closure
+    property :ast, :params, :env, :fn
+    def initialize(@ast, @params, @env, @fn)
+    end
+  end
+
+  class Type
+    alias Func = (Array(Type) -> Type)
+    alias ValueType = Nil | Bool | Int32 | String | Symbol | List | Vector | HashMap | Func | Closure | Atom
+
+    is_macro :: Bool
+    meta :: Type
+
+    property :is_macro, :meta
+
+    def initialize(@val : ValueType)
+      @is_macro = false
+      @meta = nil
+    end
+
+    def initialize(other : Type)
+      @val = other.unwrap
+      @is_macro = other.is_macro
+      @meta = other.meta
+    end
+
+    def unwrap
+      @val
+    end
+
+    def macro?
+      @is_macro
+    end
+
+    def to_s
+      pr_str(self)
+    end
+
+    def dup
+      Type.new(@val).tap do |t|
+        t.is_macro = @is_macro
+        t.meta = @meta
+      end
+    end
+
+    def ==(other : Type)
+      @val == other.unwrap
+    end
+
+    macro rel_op(*ops)
+      {% for op in ops %}
+        def {{op.id}}(other : Mal::Type)
+          l, r = @val, other.unwrap
+            {% for t in [Int32, String] %}
+              if l.is_a?({{t}}) && r.is_a?({{t}})
+                return (l) {{op.id}} (r)
+              end
+            {% end %}
+            if l.is_a?(Symbol) && r.is_a?(Symbol)
+              return l.str {{op.id}} r.str
+            end
+          false
+        end
+      {% end %}
+    end
+
+    rel_op :<, :>, :<=, :>=
+  end
+
+  alias Func = Type::Func
+end
+
+macro gen_type(t, *args)
+  Mal::Type.new {{t.id}}.new({{*args}})
+end
+
+class Array
+  def to_mal(t = Mal::List)
+    each_with_object(t.new){|e, l| l << e}
+  end
+end
+