使用Python编写一个Lisp语言的解释器

################ lis.py: Scheme Interpreter in Python 3.10
## (c) Peter Norvig, 2010-18; See http://norvig.com/lispy.html
## Type hints and minor additions by Luciano Ramalho
 
import math
import operator as op
from collections import ChainMap
from itertools import chain
from typing import Any, NoReturn
from typing import Union, List, MutableMapping, Optional, Iterator
 
Symbol = str
Atom = Union[float, int, Symbol]
Expression = Union[Atom, List]
 
Environment = MutableMapping[Symbol, object]
 
print(Atom, Expression)
print(Environment)

def parse(program: str) -> Expression:
    "Read a Scheme expression from a string."
    return read_from_tokens(tokenize(program))
 
def tokenize(s: str) -> List[str]:
    "Convert a string into a list of tokens."
    return s.replace('(', ' ( ').replace(')', ' ) ').split()
 
def read_from_tokens(tokens: List[str]) -> Expression:
    "Read an expression from a sequence of tokens."
    if len(tokens) == 0:
        raise SyntaxError('unexpected EOF while reading')
    token = tokens.pop(0)
    if '(' == token:
        exp = []
        while tokens[0] != ')':
            exp.append(read_from_tokens(tokens))
        tokens.pop(0)  # discard ')'
        return exp
    elif ')' == token:
        raise SyntaxError('unexpected )')
    else:
        return parse_atom(token)
 
def parse_atom(token: str) -> Atom:
    "Numbers become numbers; every other token is a symbol."
    try:
        return int(token)
    except ValueError:
        try:
            return float(token)
        except ValueError:
            return Symbol(token)

def standard_env() -> Environment:
    "An environment with some Scheme standard procedures."
    env: Environment = {}
    env.update(vars(math))   # sin, cos, sqrt, pi, ...
    env.update(
        {
            '+': op.add,
            '-': op.sub,
            '*': op.mul,
            '/': op.truediv, # 小数除
            'quotient': op.floordiv, # 商 地板除法 整数除
            '>': op.gt,
            '<': op.lt,
            '>=': op.ge,
            '<=': op.le,
            '=': op.eq,
            'abs': abs,
            'append': lambda *args: list(chain(*args)),          
            'apply': lambda proc, args: proc(*args),
            'begin': lambda *x: x[-1],
            '起': lambda *x: x[-1],
            'car': lambda x: x[0],
            'cdr': lambda x: x[1:],
            'cons': lambda x, y: [x] + y,
            'eq?': op.is_,
            'equal?': op.eq,
            'filter': lambda *args: list(filter(*args)),
            'length': len,
            'list': lambda *x: list(x),
            'list?': lambda x: isinstance(x, list),
            'map': lambda *args: list(map(*args)),
            'max': max,
            'min': min,
            'not': op.not_,
            'null?': lambda x: x == [],
            'number?': lambda x: isinstance(x, (int, float)),
            'procedure?': callable,
            'round': round,
            'symbol?': lambda x: isinstance(x, Symbol),
            'display': lambda x: print(lispstr(x), end=''),
            '显': lambda x: print(lispstr(x), end=''),
            'newline': lambda: print(),
        }
    )
    return env

def evaluate(x: Expression, env: Environment) -> Any:
    "Evaluate an expression in an environment."
    if isinstance(x, str):                       # variable reference
        return env[x]
    elif not isinstance(x, list):                # constant literal
        return x
    elif x[0] == 'define':                       # (define var exp)
        _, var, exp = x
        env[var] = evaluate(exp, env)
    elif x[0] == 'lambda':                       # (lambda (var...) body)
        _, parms, body = x
        return Procedure(parms, body, env)
    elif x[0] == 'quote':                        # (quote exp)
        _, exp = x
        return exp
    elif x[0] == 'if':                           # (if test consequence alternative)
        _, test, consequence, alternative = x
        if evaluate(test, env):
            return evaluate(consequence, env)
        else:
            return evaluate(alternative, env)
    elif x[0] == '设':                       # (define var exp)
        _, var, exp = x
        env[var] = evaluate(exp, env)
    elif x[0] == '函':                       # (lambda (var...) body)
        _, parms, body = x
        return Procedure(parms, body, env)
    elif x[0] == '引':                        # (quote exp)
        _, exp = x
        return exp
    elif x[0] == '若':                           # (if test consequence alternative)
        _, test, consequence, alternative = x
        if evaluate(test, env):
            return evaluate(consequence, env)
        else:
            return evaluate(alternative, env)
    else:                                        # (proc arg...)
        proc_exp, *args = x
        proc = evaluate(proc_exp, env)
        arg_values = [evaluate(exp, env) for exp in args]
        return proc(*arg_values)

def run_lines(source: str, env: Optional[Environment] = None) -> Iterator[Any]:
    global_env: Environment = ChainMap({}, standard_env())
    if env is not None:
        global_env.update(env)
    tokens = tokenize(source)
    while tokens:
        exp = read_from_tokens(tokens)
        yield evaluate(exp, global_env)
 
 
def run(source: str, env: Optional[Environment] = None) -> Any:
    # 实际上，这个函数只是简单地迭代了run_lines的所有结果，并没有对其进行任何操作。
    # 最后，返回run_lines的最后一个结果。
    for result in run_lines(source, env):
        pass
    return result

percent = """
(define a 126)
(define b (* 6 50))
(* (/ a b) 100)
"""
run(percent)

percent = """
(设 a 126)
(设 b (* 6 50))
(* (/ a b) 100)
"""
run(percent)