Class: Lisp

Inherits:
Object show all
Defined in:
lib/missinglisp.rb

Instance Method Summary collapse

Instance Method Details

#_parse(tokens) ⇒ Object 



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# File 'lib/missinglisp.rb', line 59

def _parse(tokens)
  return if tokens.empty?

  token = tokens.shift

  case token
  when :L
    list = []

    while tokens.first != :J
      raise 'unexpected end of input' if tokens.empty?

      list << _parse(tokens)
    end
    tokens.shift

    list
  when :J
    raise 'unexpected \'J\''
  else
    token
  end
end

#eval(exp, env) ⇒ Object 



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# File 'lib/missinglisp.rb', line 25

def eval(exp, env)
  return exp if exp.is_a? Numeric
  return env[exp] if exp.is_a? Symbol

  # list
  # Special forms
  if exp[0] == :quote
    return exp[1..]
  elsif exp[0] == :if
    _, test, e1, e2 = exp
    test = self.eval(test, env)
    return self.eval(e1, env) if test.is_a?(Array) && !test.empty?
    return self.eval(e1, env) unless test.is_a?(Array) || !test

    return self.eval(e2, env)
  elsif exp[0] == :define
    _, var, e = exp
    env[var] = self.eval(e, env)
    return []
  elsif exp[0] == :lambda
    _, params, e = exp
    return ->(*args) { self.eval(e, env.merge(Hash[params.zip(args)])) }
  end

  args = exp[1..].map { |c| self.eval(c, env) }
  env[exp.first]
    .call(*args)
end

#initial_env ⇒ Object 



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# File 'lib/missinglisp.rb', line 2

def initial_env
  {
    car: ->(*ls) { ls[0][0] },
    cdr: ->(*ls) { ls[0].drop 1 },
    cons: ->(e, cell, *) { [e] + cell },
    list: ->(*ls) { ls },
    add: ->(*ls) { ls.sum },
    sub: ->(hd, *tl) { tl.reduce(hd) { |sum, v| sum - v } },
    mult: ->(*ls) { ls.reduce(:*) },
    div: ->(hd, *tl) { tl.reduce(hd) { |sum, v| sum / v } },

    eq: ->(a, b, *) { a == b },
    lt: ->(a, b, *) { a < b },
    leq: ->(a, b, *) { a <= b },
    gt: ->(a, b, *) { a > b },
    geq: ->(a, b, *) { a >= b },

    p: ->(*ls) { p ls },

    nil: []
  }
end

#parse(program) ⇒ Object 



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# File 'lib/missinglisp.rb', line 54

def parse(program)
  tokens = tokenize program
  _parse tokens
end

#tokenize(s) ⇒ Object 



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# File 'lib/missinglisp.rb', line 83

def tokenize(s)
  res = []
  cur = ''
  is_reading_digit = false
  s.each_char do |c|
    case c
    when '_'
      if cur != ''
        if is_reading_digit
          res.push cur.to_i
        else
          res.push cur.to_sym
        end

        cur = ''
        is_reading_digit = false
      end
    when 'L'
      if cur != ''
        if is_reading_digit
          res.push cur.to_i
          cur = ''
          is_reading_digit = false
          res.push :L
          next
        end

        cur += 'L' and next
      end

      res.push :L
    when 'J'
      if cur != ''
        if is_reading_digit
          res.push cur.to_i
          cur = ''
          is_reading_digit = false
          res.push :J
          next
        end

        cur += 'J' and next
      end

      res.push :J
    when '0'..'9'
      cur += c and next if cur != ''

      is_reading_digit = true
      cur = c
    else
      if is_reading_digit
        res.push cur.to_i
        cur = ''
        is_reading_digit = false
      end

      cur += c
    end
  end

  res.push cur.to_sym if cur != ''

  res
end