用Python写了一个简陋Scheme解释器

from Tkinter import *

def frame(root,side):
w=Frame(root)
w.pack(side=side,expand=YES,fill=BOTH)
return w

def button(root,side,text,command=None):
w=Button(root,text=text,command=command)
w.pack(side=side,expand=YES,fill=BOTH)
return w

class Calculator(Frame):
def __init__(self):
Frame.__init__(self)
self.pack(expand=YES,fill=BOTH)
self.master.title('Simple Calculator')

display=StringVar()
Entry(self,relief=SUNKEN,
textvariable=display).pack(side=TOP,expand=YES,
fill=BOTH)[/u][/u][/u]
for key in ("123","456","789","-0."):
keyF=frame(self,TOP)
for char in key:
button(keyF,LEFT,char,
lambda w=dispay,s='%s'%char:w.set(w.get()+s))

opsF=frame(self,TOP)
for char in "+-*/=":
if char == '+':
btn=button(opsF,LEFT,char)
btn.bind('<ButtonRelease-1>',
lambda e,s=self,w=display:s.calc(w),'+')
else:
btn=button(opsF,LEFT,char,
lambda w=display,c=char:w.set(w.get()+''+c+''))

clearF=frame(self,display)
button(clearF,LEFT,'Clr',lambda w=display:w.get(''))

def calc(self,display):
try:
display.set('eval(display.get()')
except ValueError:
display.set("ERROR")

if __name__=="__main__":
Calculator().mainloop()