HCrisp/src/step8_macros.cr

#! /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