ref: 34f5a8333090c5090e1d0b6ddbaf900d64340eea
dir: /sys/src/cmd/python/Demo/threads/squasher.py/
# Coroutine example: general coroutine transfers # # The program is a variation of a Simula 67 program due to Dahl & Hoare, # (Dahl/Dijkstra/Hoare, Structured Programming; Academic Press, 1972) # who in turn credit the original example to Conway. # # We have a number of input lines, terminated by a 0 byte. The problem # is to squash them together into output lines containing 72 characters # each. A semicolon must be added between input lines. Runs of blanks # and tabs in input lines must be squashed into single blanks. # Occurrences of "**" in input lines must be replaced by "^". # # Here's a test case: test = """\ d = sqrt(b**2 - 4*a*c) twoa = 2*a L = -b/twoa R = d/twoa A1 = L + R A2 = L - R\0 """ # The program should print: # d = sqrt(b^2 - 4*a*c);twoa = 2*a; L = -b/twoa; R = d/twoa; A1 = L + R; #A2 = L - R #done # getline: delivers the next input line to its invoker # disassembler: grabs input lines from getline, and delivers them one # character at a time to squasher, also inserting a semicolon into # the stream between lines # squasher: grabs characters from disassembler and passes them on to # assembler, first replacing "**" with "^" and squashing runs of # whitespace # assembler: grabs characters from squasher and packs them into lines # with 72 character each, delivering each such line to putline; # when it sees a null byte, passes the last line to putline and # then kills all the coroutines # putline: grabs lines from assembler, and just prints them from Coroutine import * def getline(text): for line in string.splitfields(text, '\n'): co.tran(codisassembler, line) def disassembler(): while 1: card = co.tran(cogetline) for i in range(len(card)): co.tran(cosquasher, card[i]) co.tran(cosquasher, ';') def squasher(): while 1: ch = co.tran(codisassembler) if ch == '*': ch2 = co.tran(codisassembler) if ch2 == '*': ch = '^' else: co.tran(coassembler, ch) ch = ch2 if ch in ' \t': while 1: ch2 = co.tran(codisassembler) if ch2 not in ' \t': break co.tran(coassembler, ' ') ch = ch2 co.tran(coassembler, ch) def assembler(): line = '' while 1: ch = co.tran(cosquasher) if ch == '\0': break if len(line) == 72: co.tran(coputline, line) line = '' line = line + ch line = line + ' ' * (72 - len(line)) co.tran(coputline, line) co.kill() def putline(): while 1: line = co.tran(coassembler) print line import string co = Coroutine() cogetline = co.create(getline, test) coputline = co.create(putline) coassembler = co.create(assembler) codisassembler = co.create(disassembler) cosquasher = co.create(squasher) co.tran(coputline) print 'done' # end of example