Re: --pirate and coroutines

[Leopold Toetsch]

Michal wrote:
Hey all,
Why does --python mode modify the
behaviour of coroutines?
Guido is to blame. Python generators/coroutines work like this:
  iter = coro()     # first time calling
  for x = iter() ...# iterate
And that's what Parrot is doing too with the --python switch. But there 
is more ugliness: Python returns "None" if the generator is left through 
the end and a StopIteration is thrown (which you have to catch).

That's all really messy and needs definitely some cleanup. OTOH it was 
the most straight forward translation of Python bytecode.

$ parrot --python pcoro.txt
StopIteration
        in file '(unknown file)' near line -1
ab
$ cat pcoro.txt
.sub __main__
    .local object gen
    .local object res
    .local object iter
    gen = global "_gen_g"
    iter = gen()
    .local pmc None
    None = new .None
loop:
    unless iter, ex
    res = shift iter
    if res == None goto ex
    print res
    goto loop
ex:
    end
.end
.sub _gen_g prototyped
    .local object res
    res = new PerlString
    res = "a"
    .pcc_begin_yield
    .return res
    .pcc_end_yield
    res = "b"
    .pcc_begin_yield
    .return res
    .pcc_end_yield
    .local pmc None
    None = new .None
    .pcc_begin_return
    .return None
    .pcc_end_return
.end