crystal/step4_if_fn_do.cr

   1 #! /usr/bin/env crystal run
   2
   3 require "./readline"
   4 require "./reader"
   5 require "./printer"
   6 require "./types"
   7 require "./env"
   8 require "./core"
   9 require "./error"
  10
  11 # Note:
  12 # Employed downcase names because Crystal prohibits uppercase names for methods
  13
  14 def func_of(env, binds, body)
  15   -> (args : Array(Mal::Type)) {
  16     new_env = Mal::Env.new(env, binds, args)
  17     eval(body, new_env)
  18   } as Mal::Func
  19 end
  20
  21 def eval_ast(ast, env)
  22   return ast.map{|n| eval(n, env) as Mal::Type} if ast.is_a? Mal::List
  23
  24   val = ast.unwrap
  25
  26   Mal::Type.new case val
  27   when Mal::Symbol
  28     if e = env.get(val.str)
  29       e
  30     else
  31       eval_error "'#{val.str}' not found"
  32     end
  33   when Mal::List
  34     val.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
  35   when Mal::Vector
  36     val.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
  37   when Mal::HashMap
  38     val.each{|k, v| val[k] = eval(v, env)}
  39     val
  40   else
  41     val
  42   end
  43 end
  44
  45 def read(str)
  46   read_str str
  47 end
  48
  49 def eval(ast, env)
  50   list = ast.unwrap
  51
  52   return eval_ast(ast, env)          unless list.is_a? Mal::List
  53   return Mal::Type.new Mal::List.new if list.empty?
  54
  55   head = list.first.unwrap
  56
  57   Mal::Type.new case head
  58   when Mal::Symbol
  59     case head.str
  60     when "def!"
  61       eval_error "wrong number of argument for 'def!'" unless list.size == 3
  62       a1 = list[1].unwrap
  63       eval_error "1st argument of 'def!' must be symbol" unless a1.is_a? Mal::Symbol
  64       env.set(a1.str, eval(list[2], env))
  65     when "let*"
  66       eval_error "wrong number of argument for 'def!'" unless list.size == 3
  67
  68       bindings = list[1].unwrap
  69       eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
  70       eval_error "size of binding list must be even" unless bindings.size.even?
  71
  72       new_env = Mal::Env.new env
  73       bindings.each_slice(2) do |binding|
  74         key, value = binding
  75         name = key.unwrap
  76         eval_error "name of binding must be specified as symbol" unless name.is_a? Mal::Symbol
  77         new_env.set(name.str, eval(value, new_env))
  78       end
  79
  80       eval(list[2], new_env)
  81     when "do"
  82       list.shift(1)
  83       eval_ast(list, env).last
  84     when "if"
  85       cond = eval(list[1], env)
  86       case cond
  87       when Nil
  88         list.size >= 4 ? eval(list[3], env) : nil
  89       when false
  90         list.size >= 4 ?  eval(list[3], env) : nil
  91       else
  92         eval(list[2], env)
  93       end
  94     when "fn*"
  95       # Note:
  96       # If writing lambda expression here directly, compiler will fail to infer type of 'list'. (Error 'Nil for empty?')
  97       func_of(env, list[1].unwrap, list[2])
  98     else
  99       f = eval_ast(list.first, env).unwrap
 100       eval_error "expected function symbol as the first symbol of list" unless f.is_a? Mal::Func
 101       list.shift(1)
 102       f.call eval_ast(list, env)
 103     end
 104   else
 105     f = eval(list.first, env).unwrap
 106     eval_error "expected function symbol as the first symbol of list" unless f.is_a? Mal::Func
 107     list.shift(1)
 108     f.call eval_ast(list, env)
 109   end
 110 end
 111
 112 def print(result)
 113   pr_str(result, true)
 114 end
 115
 116 def rep(str)
 117   print(eval(read(str), $repl_env))
 118 end
 119
 120 $repl_env = Mal::Env.new nil
 121 Mal::NS.each{|k,v| $repl_env.set(k, Mal::Type.new(v))}
 122
 123 while line = my_readline("user> ")
 124   begin
 125     puts rep(line)
 126   rescue e
 127     STDERR.puts e
 128   end
 129 end