Beam interpreter in Pyhton

beam.py

#!/usr/bin/python

import sys


if(len(sys.argv) < 5):
  print 'Usage: ./beam.py path <debug> <debugpoints> <memsize>'
  print '  debug: on or off'
  print '  debugpoints: ;-seperated list of coordinates (e.g. 0,9;0,2)'
  print '               (use -1,-1 for none)'
  print '  memsize: how many memory cells'
  sys.exit(-3)
  
debug = False
cycles = 0
bps = sys.argv[3].split(';')
bps = map(lambda a: a.split(','),bps)
bps = map(lambda ds: (int(ds[0]),int(ds[1])),bps)
memsize = int(sys.argv[4])

if(sys.argv[2] == 'on'):
  debug = True
elif(sys.argv[2] == 'off'):
  debug = False
else:
  print 'Unknown option: ' + sys.argv[2]
  sys.exit(-2)

fpath = sys.argv[1]

fhandle = open(fpath, 'r')
fcontents = fhandle.read()

lines = fcontents.splitlines()
chars = map(list,lines)


x = 0
y = 0
h = len(lines)
xd = 1
yd = 0
beam = 0
store = 0
memory = [0] * memsize

while True:



  cycles += 1

  if y < 0 or y >= h:
    sys.stderr.write("y out of bounds: " + str(x) + "," + str(y) + "\n")
    sys.exit(-1)
    
  w = len(lines[y])
  if x < 0 or x >= w:
    sys.stderr.write("x out of bounds: " + str(x) + "," + str(y) + "\n")
    sys.exit(-2)
    
  if((x,y) in bps):
    print
    print '== DEBUGPOINT =='
    print 'Beam := %d, Store := %d' % (beam, store)
    print 'Cycles := %d' % (cycles)
    print 'C := %s' % (lines[y][x])
    print ' ** MEMORY **'
    print memory
      
    
  c = lines[y][x]
  
  if(debug): print '%d,%d: %s ; %d,%d' % (x,y,c,beam,store)
  
  if(c == 'H'):
    break
  elif(c == '>'):
    xd = 1; yd = 0
  elif(c == '<'):
    xd = -1; yd = 0
  elif(c == '^'):
    yd = -1; xd = 0
  elif(c == 'v'):
    yd = 1; xd = 0
  elif(c == '+'):
    beam += 1
    if(beam >= 256): beam = 0
  elif(c == '-'):
    beam -= 1
    if(beam < 0): beam = 255
  elif(c == '@'):
    sys.stdout.write(chr(beam))
  elif(c == ':'):
    sys.stdout.write(str(beam))
  elif(c == '/'):
    if(xd == -1):
      yd = 1; xd = 0;
    elif(yd == -1):
      xd = 1; yd = 0;
    elif(xd == 1):
      yd = -1; xd = 0;
    elif(yd == 1):
      xd = -1; yd = 0;
  elif(c == '\\'):
    if(xd == 1):
      yd = 1; xd = 0;
    elif(yd == -1):
      xd = -1; yd = 0;
    elif(yd == 1):
      xd = 1; yd = 0;
    elif(xd == -1):
      yd = -1; xd = 0
  elif(c == '!'):
    if(beam != 0):
      xd *= -1
      yd *= -1
  elif(c == '?'):
    if(beam == 0):
      xd *= -1
      yd *= -1
  elif(c == '|'):
    if(yd == 0):
      xd *= -1; yd = 0
  elif(c == '_'):
    if(xd == 0):
      yd *= -1; xd = 0
  elif(c == 'S'):
    store = beam
  elif(c == 'L'):
    beam = store
    beam %= 256
  elif(c == 's'):
    memory[beam] = store % 256
  elif(c == 'g'):
    store = memory[beam]
  elif(c == 'P'):
    memory[store] = beam
  elif(c == 'p'):
    beam = memory[store]
  elif(c == 'u'):
    if(beam != store):
      yd = -1; xd = 0;
  elif(c == 'n'):
    if(beam != store):
      yd = 1; xd = 0;
  elif(c == '`'):
    store -= 1
    if(store < 0): store = 255
  elif(c == '\''):
    store += 1
  elif(c == ')'):
    if(store != 0): xd = -1; yd = 0;
  elif(c == '('):
    if(store != 0): xd = 1; yd = 0;
  elif(c == 'r'):
    s = sys.stdin.read(1)
    if(len(s) != 0):
      beam = ord(s)
    else:
      beam = 0
    
    
    
  x += xd
  y += yd
  
print ""
print ""
print "Took %d cycles." % (cycles)

Hi, with the store decrementer the value is set to 255 if less than 0, but there is no reciprocal rule on the incrementer.

The store is an arbitrarily large positive integer as by the Beam specification.

However, line

if(beam < 0): beam = 256

should be beam = 255. I'll fix it.

fixed