# File lib/type_checker.rb, line 597
  def process_iasgn(exp)
    var = exp.shift
    val = process exp.shift

    var_type = @env.lookup var rescue nil
    if var_type.nil? then
      @env.add var, val.sexp_type
    else
      val.sexp_type.unify var_type
    end

    return t(:iasgn, var, val, val.sexp_type)
  end