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 # (Dahl/Dijkstra/Hoare, Structured Programming; Academic Press, 1972)
   5 # who in turn credit the original example to Conway.
   6 #
   7 # We have a number of input lines, terminated by a 0 byte.  The problem
   8 # is to squash them together into output lines containing 72 characters
   9 # each.  A semicolon must be added between input lines.  Runs of blanks
  10 # and tabs in input lines must be squashed into single blanks.
  11 # Occurrences of "**" in input lines must be replaced by "^".
  12 #
  13 # Here's a test case:
  14
  15 test = """\
  16    d    =   sqrt(b**2  -  4*a*c)
  17 twoa    =   2*a
  18    L    =   -b/twoa
  19    R    =   d/twoa
  20   A1    =   L + R
  21   A2    =   L - R\0
  22 """
  23
  24 # The program should print:
  25
  26 # d = sqrt(b^2 - 4*a*c);twoa = 2*a; L = -b/twoa; R = d/twoa; A1 = L + R;
  27 #A2 = L - R
  28 #done
  29
  30 # getline: delivers the next input line to its invoker
  31 # disassembler: grabs input lines from getline, and delivers them one
  32 #    character at a time to squasher, also inserting a semicolon into
  33 #    the stream between lines
  34 # squasher:  grabs characters from disassembler and passes them on to
  35 #    assembler, first replacing "**" with "^" and squashing runs of
  36 #    whitespace
  37 # assembler: grabs characters from squasher and packs them into lines
  38 #    with 72 character each, delivering each such line to putline;
  39 #    when it sees a null byte, passes the last line to putline and
  40 #    then kills all the coroutines
  41 # putline: grabs lines from assembler, and just prints them
  42
  43 from Coroutine import *
  44
  45 def getline(text):
  46     for line in string.splitfields(text, '\n'):
  47         co.tran(codisassembler, line)
  48
  49 def disassembler():
  50     while 1:
  51         card = co.tran(cogetline)
  52         for i in range(len(card)):
  53             co.tran(cosquasher, card[i])
  54         co.tran(cosquasher, ';')
  55
  56 def squasher():
  57     while 1:
  58         ch = co.tran(codisassembler)
  59         if ch == '*':
  60             ch2 = co.tran(codisassembler)
  61             if ch2 == '*':
  62                 ch = '^'
  63             else:
  64                 co.tran(coassembler, ch)
  65                 ch = ch2
  66         if ch in ' \t':
  67             while 1:
  68                 ch2 = co.tran(codisassembler)
  69                 if ch2 not in ' \t':
  70                     break
  71             co.tran(coassembler, ' ')
  72             ch = ch2
  73         co.tran(coassembler, ch)
  74
  75 def assembler():
  76     line = ''
  77     while 1:
  78         ch = co.tran(cosquasher)
  79         if ch == '\0':
  80             break
  81         if len(line) == 72:
  82             co.tran(coputline, line)
  83             line = ''
  84         line = line + ch
  85     line = line + ' ' * (72 - len(line))
  86     co.tran(coputline, line)
  87     co.kill()
  88
  89 def putline():
  90     while 1:
  91         line = co.tran(coassembler)
  92         print line
  93
  94 import string
  95 co = Coroutine()
  96 cogetline = co.create(getline, test)
  97 coputline = co.create(putline)
  98 coassembler = co.create(assembler)
  99 codisassembler = co.create(disassembler)
 100 cosquasher = co.create(squasher)
 101
 102 co.tran(coputline)
 103 print 'done'
 104
 105 # end of example