User:Marinus/Minimal-2D interpreter

#!/usr/bin/env python
# Minimal-2D interpreter

import sys

def addvec((x1,y1),(x2,y2)):
   return (x1+x2, y1+y2)
def mulvec((x,y),m):
   return (x*m, y*m)

# bidirectional infinite tape
class Tape:
   def __init__(self):
      self.tape = [0]
      self.offset = 0
      self.pos = 0
   
   def left(self):
      self.pos -= 1
      if self.pos == -1:
         self.offset += 1
         self.pos = 0
         self.tape.insert(0, 0)
   
   def right(self):
      self.pos += 1
      if len(self.tape) >= self.pos + self.offset:
         self.tape.append(0)
   
   def get(self):
      return self.tape[self.pos+self.offset]
   
   def set(self, v):
      self.tape[self.pos+self.offset] = v

# program field
class Field:
   def __init__(self, f, emptychar=' '):
      self.lines = [line[:-1] for line in f.readlines()]
      self.ybound = len(self.lines)
      self.xbound = max([len(line) for line in self.lines])
      self.emptychar = emptychar
      
   def __getitem__(self, (x, y)):
      if 0<=x<self.xbound and 0<=y<self.ybound:
         try:
            return self.lines[y][x]
         except IndexError:
            return self.emptychar 
      else:
         raise IndexError("coordinates are outside field")
         
         
# program head
class Head:
   U,D,L,R = (0,-1), (0,1), (-1,0), (1,0)
   def __init__(self, tape, field):
      self.tape=tape
      self.field=field
      self.ip=[0,0]
      self.dir=self.R
      
      self.cmds = { '<': self.tape.left, 
                    '>': self.tape.right,
                    '+': self.inc,
                    '-': self.dec,
                    '.': self.out,
                    ',': self.inp,
                    '/': self.skip,
                    'U': self.sdir(self.U),
                    'D': self.sdir(self.D),
                    'L': self.sdir(self.L),
                    'R': self.sdir(self.R) }
                    
   def inc(self): self.tape.set(self.tape.get()+1)
   def dec(self): self.tape.set(self.tape.get()-1)
   def out(self): sys.stdout.write(chr(self.tape.get()%256))
   def inp(self):
      ch = sys.stdin.read(1)
      self.tape.set(ch and ord(ch) or -1)
   def skip(self): self.ip = addvec(self.ip, mulvec(self.dir, not self.tape.get()))
   def sdir(self, d):
      def f():
         self.dir=d
      return f
   
   def step(self):
      try:
         if self.field[self.ip] in self.cmds.keys():
            self.cmds[self.field[self.ip]]()
         self.ip = addvec(self.ip, self.dir)
         return True
      except IndexError:
         # end program, we've left the field
         return False
         
         
def main(argv):
   if len(argv) != 2:
      print "usage: %s program" % argv[0]
      sys.exit()
   
   try:
      h = Head(Tape(), Field(file(argv[1])))
      while h.step(): pass
   except IOError, e:
      print "error: can't read %s: %s" % (argv[1], e)

if __name__=='__main__': main(sys.argv)