crystal/step5_tco.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 module Mal
  15   extend self
  16
  17   def func_of(env, binds, body)
  18     -> (args : Array(Mal::Type)) {
  19       new_env = Mal::Env.new(env, binds, args)
  20       eval(body, new_env)
  21     } as Mal::Func
  22   end
  23
  24   def eval_ast(ast, env)
  25     return ast.map{|n| eval(n, env) as Mal::Type} if ast.is_a? Mal::List
  26
  27     val = ast.unwrap
  28
  29     Mal::Type.new case val
  30     when Mal::Symbol
  31       if e = env.get(val.str)
  32         e
  33       else
  34         eval_error "'#{val.str}' not found"
  35       end
  36     when Mal::List
  37       val.each_with_object(Mal::List.new){|n, l| l << eval(n, env)}
  38     when Mal::Vector
  39       val.each_with_object(Mal::Vector.new){|n, l| l << eval(n, env)}
  40     when Array(Mal::Type)
  41       val.map{|n| eval(n, env)}
  42     when Mal::HashMap
  43       val.each{|k, v| val[k] = eval(v, env)}
  44       val
  45     else
  46       val
  47     end
  48   end
  49
  50   def eval_invocation(list, env)
  51     f = eval(list.first, env).unwrap
  52     case f
  53     when Mal::Closure
  54       f.fn.call eval_ast(list[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, env)
  55     when Mal::Func
  56       f.call eval_ast(list[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, env)
  57     else
  58       eval_error "expected function as the first argument"
  59     end
  60   end
  61
  62   def read(str)
  63     read_str str
  64   end
  65
  66   macro invoke_list(l)
  67     f = eval({{l}}.first, env).unwrap
  68     args = eval_ast({{l}}[1..-1].each_with_object(Mal::List.new){|i, l| l << i}, env)
  69     case f
  70     when Mal::Closure
  71       ast = f.ast
  72       env = Mal::Env.new(f.env, f.params, args)
  73       next # TCO
  74     when Mal::Func
  75       return f.call args
  76     else
  77       eval_error "expected function as the first argument"
  78     end
  79   end
  80
  81   def eval(ast, env)
  82     # 'next' in 'do...end' has a bug in crystal 0.7.1
  83     # https://github.com/manastech/crystal/issues/659
  84     while true
  85       list = ast.unwrap
  86
  87       return eval_ast(ast, env) unless list.is_a? Mal::List
  88       return gen_type Mal::List if list.empty?
  89
  90       head = list.first.unwrap
  91
  92       unless head.is_a? Mal::Symbol
  93         invoke_list list
  94       end
  95
  96       return Mal::Type.new case head.str
  97         when "def!"
  98           eval_error "wrong number of argument for 'def!'" unless list.size == 3
  99           a1 = list[1].unwrap
 100           eval_error "1st argument of 'def!' must be symbol" unless a1.is_a? Mal::Symbol
 101           env.set(a1.str, eval(list[2], env))
 102         when "let*"
 103           eval_error "wrong number of argument for 'def!'" unless list.size == 3
 104
 105           bindings = list[1].unwrap
 106           eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
 107           eval_error "size of binding list must be even" unless bindings.size.even?
 108
 109           new_env = Mal::Env.new env
 110           bindings.each_slice(2) do |binding|
 111             key, value = binding
 112             name = key.unwrap
 113             eval_error "name of binding must be specified as symbol" unless name.is_a? Mal::Symbol
 114             new_env.set(name.str, eval(value, new_env))
 115           end
 116
 117           ast, env = list[2], new_env
 118           next # TCO
 119         when "do"
 120           if list.empty?
 121             ast = Mal::Type.new nil
 122             next
 123           end
 124
 125           eval_ast(list[1..-2].each_with_object(Mal::List.new){|i,l| l << i}, env)
 126           ast = list.last
 127           next # TCO
 128         when "if"
 129           ast = unless eval(list[1], env).unwrap
 130             list.size >= 4 ? list[3] : Mal::Type.new(nil)
 131           else
 132             list[2]
 133           end
 134           next # TCO
 135         when "fn*"
 136           # Note:
 137           # If writing lambda expression here directly, compiler will fail to infer type of 'list'. (Error 'Nil for empty?')
 138           params = list[1].unwrap
 139           unless params.is_a?(Mal::List) || params.is_a?(Mal::Vector)
 140             eval_error "'fn*' parameters must be list"
 141           end
 142           Mal::Closure.new(list[2], params, env, func_of(env, list[1].unwrap, list[2]))
 143         else
 144           invoke_list list
 145         end
 146     end
 147   end
 148
 149   def print(result)
 150     pr_str(result, true)
 151   end
 152
 153   def rep(str)
 154     print(eval(read(str), $repl_env))
 155   end
 156 end
 157
 158 $repl_env = Mal::Env.new nil
 159 Mal::NS.each{|k,v| $repl_env.set(k, Mal::Type.new(v))}
 160 Mal.rep "(def! not (fn* (a) (if a false true)))"
 161
 162 while line = my_readline("user> ")
 163   begin
 164     puts Mal.rep(line)
 165   rescue e
 166     STDERR.puts e
 167   end
 168 end