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  "signature": "sha256:0d0a916691e6035e241a2d6097ddd91a4515843d8bdb4727bed7f2fa742e7912"
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 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "code",
     "collapsed": true,
     "input": [
      "import time"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%time\n",
      "\n",
      "time.sleep(.138)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "CPU times: user 446 \u00b5s, sys: 1 \u00b5s, total: 447 \u00b5s\n",
        "Wall time: 138 ms\n"
       ]
      }
     ],
     "prompt_number": 11
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%%time\n",
      "\n",
      "time.sleep(.000639 * 10)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "CPU times: user 311 \u00b5s, sys: 0 ns, total: 311 \u00b5s\n",
        "Wall time: 6.52 ms\n"
       ]
      }
     ],
     "prompt_number": 20
    },
    {
     "cell_type": "code",
     "collapsed": true,
     "input": [
      "class Symbol(str):\n",
      "    \"Class to define symbols, which should be unique items\"\n",
      "    def __repr__(self):\n",
      "        return str.__repr__(self)[1:-1] # don't show quotation marks\n",
      "    \n",
      "EmptyList = Symbol(\"()\")\n",
      "void = Symbol(\"<void>\")\n",
      "        \n",
      "class Cons(object):\n",
      "    \"A cell/link used to construct linked-list\"\n",
      "    def __init__(self, car, cdr):\n",
      "        self.car = car\n",
      "        self.cdr = cdr\n",
      "    def __repr__(self):\n",
      "        if self.car == \"closure-exp\":\n",
      "            return \"#<procedure>\"\n",
      "        retval = \"\"\n",
      "        current = self\n",
      "        while current is not EmptyList and isinstance(current, Cons):\n",
      "            if retval != \"\":\n",
      "                retval += \" \"\n",
      "            retval += str(current.car) # recursion here!\n",
      "            current = current.cdr\n",
      "        if current is not EmptyList:\n",
      "            retval += \" . \" + str(current)\n",
      "        return \"(%s)\" % retval\n",
      "             \n",
      "class String(str):\n",
      "    \"Class to wrap strings so that we can define repr\"\n",
      "    def __repr__(self):\n",
      "        return '\"%s\"' % str.__repr__(self)[1:-1]\n",
      "    def __str__(self):\n",
      "        return self.__repr__()\n",
      "\n",
      "def List(*args):\n",
      "    \"Create a linked-list of items\"\n",
      "    retval = EmptyList\n",
      "    for arg in reversed(args):\n",
      "        retval = cons(arg, retval)\n",
      "    return retval\n",
      "        \n",
      "def car(exp):\n",
      "    return exp.car\n",
      "def cadr(exp):\n",
      "    return exp.cdr.car\n",
      "def caddr(exp):\n",
      "    return exp.cdr.cdr.car\n",
      "def cadddr(exp):\n",
      "    return exp.cdr.cdr.cdr.car\n",
      "\n",
      "def cdr(exp):\n",
      "    return exp.cdr\n",
      "def cddr(exp):\n",
      "    return exp.cdr.cdr\n",
      "def cdddr(exp):\n",
      "    return exp.cdr.cdr.cdr\n",
      "def cddddr(exp):\n",
      "    return exp.cdr.cdr.cdr.cdr\n",
      "\n",
      "def cons(item1, item2):\n",
      "    return Cons(item1, item2)\n",
      "\n",
      "def length(item, handler):\n",
      "    current = item\n",
      "    count = 0\n",
      "    while current is not EmptyList and isinstance(current, Cons):\n",
      "        current = current.cdr\n",
      "        count += 1\n",
      "    if current is not EmptyList:\n",
      "        return handler(\"Attempt to take length of improper list\")\n",
      "    return count\n",
      "\n",
      "def rac(item):\n",
      "    current = item\n",
      "    previous = None\n",
      "    while current is not EmptyList:\n",
      "        previous = current.car\n",
      "        current = current.cdr\n",
      "    return previous\n",
      "\n",
      "## We use \"_q\" in Python to represent \"?\" in Scheme.\n",
      "\n",
      "def pair_q(item):\n",
      "    return isinstance(item, Cons)\n",
      "\n",
      "def null_q(lst):\n",
      "    return lst is EmptyList"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 28
    },
    {
     "cell_type": "code",
     "collapsed": true,
     "input": [
      "def list_to_vector(lst):\n",
      "    retval = []\n",
      "    current = lst\n",
      "    while current is not EmptyList:\n",
      "        retval.append(current.car)\n",
      "        current = current.cdr\n",
      "    return retval\n",
      "\n",
      "def extend_env(vars, vals, env):\n",
      "    return [dict(map(list,zip(list_to_vector(vars), \n",
      "                              list_to_vector(vals)))), env]"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 32
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "extend_env(List(\"x\", \"y\"), List(1, 2), [])"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 33,
       "text": [
        "[{'x': 1, 'y': 2}, []]"
       ]
      }
     ],
     "prompt_number": 33
    },
    {
     "cell_type": "code",
     "collapsed": true,
     "input": [],
     "language": "python",
     "metadata": {},
     "outputs": []
    }
   ],
   "metadata": {}
  }
 ]
}