Python实现Scheme

近一周，学习Scheme有点上瘾，我对Scheme的兴趣源自其简单的语法，只有成对的()。学习Scheme，加上自己的Python编程，能很快的抄出一个Scheme解释器：

https://github.com/zhangyun00...

仔细看程序注释里的论文链接，介绍了绍python实现的scheme子集。我拿来改了改，加了for和while循环，break跳出循环，可以使用元组、列表，字典，class定义类。

运行python ZhScheme.py

ZhScheme> (tuple 1 2)
['tuple', 1, 2]
(1, 2)
ZhScheme> (list  5 6 6 )
['list', 5, 6, 6]
[5, 6, 6]
ZhScheme> (dict (list (list 5 6) (list 56 34 )))
['dict', ['list', ['list', 5, 6], ['list', 56, 34]]]
{5: 6, 56: 34}
ZhScheme> (sin 12)
['sin', 12]-0.5365729180004349ZhScheme> (sin 34)
['sin', 34]0.5290826861200238ZhScheme> (list 3 4 5)
['list', 3, 4, 5]
(3 4 5)
ZhScheme> (list (list 3 4 5) (list 456  45))
['list', ['list', 3, 4, 5], ['list', 456, 45]]
((3 4 5) (456 45ZhScheme> (define i 4)
['define', 'i', 4]
ZhScheme> ii4ZhScheme> (while (< i 23) (begin (print i) (set i (+ i 1))(if (eq? i 12) break))
)
['while', ['<', 'i', 23], ['begin', ['print', 'i'], ['set', 'i', ['+', 'i', 1]],
 ['if', ['eq?', 'i', 12], 'break']]]4567891011ZhScheme> (for (set i 23) (< i 45) (set i (+ i 2)) (begin (print i) (if (eq? i3) break)))
['for', ['set', 'i', 23], ['<', 'i', 45], ['set', 'i', ['+', 'i', 2]], ['begin'
 ['print', 'i'], ['if', ['eq?', 'i', 43], 'break']]]2325272931333537394143ZhScheme> (env)
['env']
variables ...

+  :  <built-in function add>-  :  <built-in function sub>*  :  <built-in function mul>/  :  <built-in function truediv>>  :  <built-in function gt><  :  <built-in function lt>>=  :  <built-in function ge><=  :  <built-in function le>=  :  <built-in function eq>not  :  <built-in function not_>eq?  :  <built-in function is_>equal?  :  <built-in function eq>max  :  <built-in function max>min  :  <built-in function min>abs  :  <built-in function abs>round  :  <built-in function round>car  :  <function <lambda> at 0x0000cdr  :  <function <lambda> at 0x0000list  :  <function <lambda> at 0x000list-ref  :  <function <lambda> at 0append  :  <built-in function add>len  :  <built-in function len>map  :  <class 'map'>
print  :  <built-in function print>exit  :  Use exit() or Ctrl-Z plus R
open  :  <function <lambda> at 0x000call/cc  :  <function callcc at 0x00procedure?  :  <built-in function canull?  :  <function <lambda> at 0x00number?  :  <function <lambda> at 0xstring?  :  <function <lambda> at 0xlist?  :  <function <lambda> at 0x00struct?  :  <function <lambda> at 0xdict?  :  <function <lambda> at 0x00int  :  {}
__name__  :  math
__doc__  :  This module is always av
mathematical functions defined by th
__package__  :
__loader__  :  <class '_frozen_impor
__spec__  :  ModuleSpec(name='math',
orter'>, origin='built-in')acos  :  <built-in function acos>acosh  :  <built-in function acosh>asin  :  <built-in function asin>asinh  :  <built-in function asinh>atan  :  <built-in function atan>atan2  :  <built-in function atan2>atanh  :  <built-in function atanh>ceil  :  <built-in function ceil>copysign  :  <built-in function copycos  :  <built-in function cos>cosh  :  <built-in function cosh>degrees  :  <built-in function degreerf  :  <built-in function erf>erfc  :  <built-in function erfc>exp  :  <built-in function exp>expm1  :  <built-in function expm1>fabs  :  <built-in function fabs>factorial  :  <built-in function facfloor  :  <built-in function floor>fmod  :  <built-in function fmod>frexp  :  <built-in function frexp>fsum  :  <built-in function fsum>gamma  :  <built-in function gamma>gcd  :  <built-in function gcd>hypot  :  <built-in function hypot>isclose  :  <built-in function iscloisfinite  :  <built-in function isfiisinf  :  <built-in function isinf>isnan  :  <built-in function isnan>ldexp  :  <built-in function ldexp>lgamma  :  <built-in function lgammalog  :  <built-in function log>log1p  :  <built-in function log1p>log10  :  <built-in function log10>log2  :  <built-in function log2>modf  :  <built-in function modf>pow  :  <built-in function pow>radians  :  <built-in function radiasin  :  <built-in function sin>sinh  :  <built-in function sinh>sqrt  :  <built-in function sqrt>tan  :  <built-in function tan>tanh  :  <built-in function tanh>trunc  :  <built-in function trunc>pi  :  3.141592653589793e  :  2.718281828459045tau  :  6.283185307179586inf  :  infnan  :  nani  :  43struct ...

总之，这个scheme的目标是可以调用Python里的各种常用函数，以上env结果中的变量和函数都是你可以使用的。

现在可解释执行，以行为单位的文件了：

python ZhScheme.py test.s

test.s文件内容：

(quote must write code as lines)

(+ 2 5)

(define i 1)i(if (< i 19) (print (+ i 1)))
(while (< i 23) (begin (print i) (set i (+ i 1))(if (eq? i 12) break)))
(for (set i 23) (< i 45) (set i (+ i 2)) (begin (print i) (if (eq? i 43) break)))

(define f (open test.ss r))
((. f read))

(define define 12)

define

(class point (list (list n 2)(list m (lambda x (* 2 x)))))
(define x (point))
(. x n)
((. x m) 4)

有在ZhScheme加入静态数据类型的想法，也就是说，除了能define x 12之外，还可以使用 int y 34，定义一个整形变量，如果set y 2.3会导致一个类型错误 -- 把浮点值付给了整型值，多数静态类型语言都是这么做的。