Demo/threads/squasher.py

   1 # Coroutine example:  general coroutine transfers
   2 #
   3 # The program is a variation of a Simula 67 program due to Dahl & Hoare,
   4 # who in turn credit the original example to Conway.
   5 #
   6 # We have a number of input lines, terminated by a 0 byte.  The problem
   7 # is to squash them together into output lines containing 72 characters
   8 # each.  A semicolon must be added between input lines.  Runs of blanks
   9 # and tabs in input lines must be squashed into single blanks.
  10 # Occurrences of "**" in input lines must be replaced by "^".
  11 #
  12 # Here's a test case:
  13
  14 test = """\
  15    d    =   sqrt(b**2  -  4*a*c)
  16 twoa    =   2*a
  17    L    =   -b/twoa
  18    R    =   d/twoa
  19   A1    =   L + R
  20   A2    =   L - R\0
  21 """
  22
  23 # The program should print:
  24
  25 # d = sqrt(b^2 - 4*a*c);twoa = 2*a; L = -b/twoa; R = d/twoa; A1 = L + R;
  26 #A2 = L - R
  27 #done
  28
  29 # getline: delivers the next input line to its invoker
  30 # disassembler: grabs input lines from getline, and delivers them one
  31 #    character at a time to squasher, also inserting a semicolon into
  32 #    the stream between lines
  33 # squasher:  grabs characters from disassembler and passes them on to
  34 #    assembler, first replacing "**" with "^" and squashing runs of
  35 #    whitespace
  36 # assembler: grabs characters from squasher and packs them into lines
  37 #    with 72 character each, delivering each such line to putline;
  38 #    when it sees a null byte, passes the last line to putline and
  39 #    then kills all the coroutines
  40 # putline: grabs lines from assembler, and just prints them
  41
  42 from Coroutine import *
  43
  44 def getline(text):
  45     for line in string.splitfields(text, '\n'):
  46         co.back(line)
  47
  48 def disassembler():
  49     while 1:
  50         card = co.tran(cogetline)
  51         for i in range(len(card)):
  52             co.tran(cosquasher, card[i])
  53         co.tran(cosquasher, ';')
  54
  55 def squasher():
  56     while 1:
  57         ch = co.tran(codisassembler)
  58         if ch == '*':
  59             ch2 = co.tran(codisassembler)
  60             if ch2 == '*':
  61                 ch = '^'
  62             else:
  63                 co.tran(coassembler, ch)
  64                 ch = ch2
  65         if ch in ' \t':
  66             while 1:
  67                 ch2 = co.tran(codisassembler)
  68                 if ch2 not in ' \t':
  69                     break
  70             co.tran(coassembler, ' ')
  71             ch = ch2
  72         co.tran(coassembler, ch)
  73
  74 def assembler():
  75     line = ''
  76     while 1:
  77         ch = co.tran(cosquasher)
  78         if ch == '\0':
  79             break
  80         if len(line) == 72:
  81             co.tran(coputline, line)
  82             line = ''
  83         line = line + ch
  84     line = line + ' ' * (72 - len(line))
  85     co.tran(coputline, line)
  86     co.kill()
  87
  88 def putline():
  89     while 1:
  90         line = co.tran(coassembler)
  91         print line
  92
  93 import string
  94 co = Coroutine()
  95 cogetline = co.create(getline, test)
  96 coputline = co.create(putline)
  97 coassembler = co.create(assembler)
  98 codisassembler = co.create(disassembler)
  99 cosquasher = co.create(squasher)
 100
 101 co.tran(coputline)
 102 print 'done'
 103
 104 # end of example