[Python-checkins] peps: PEP 403: Try a simple goless example

[nick.coghlan]

http://hg.python.org/peps/rev/98e70c0223ea
changeset:   5506:98e70c0223ea
user:        Nick Coghlan <ncoghlan at gmail.com>
date:        Sat Jul 26 01:59:36 2014 +1000
summary:
  PEP 403: Try a simple goless example

files:
  pep-0403.txt |  98 +++++++++++++++++++++++++++++++++++++++-
  1 files changed, 97 insertions(+), 1 deletions(-)


diff --git a/pep-0403.txt b/pep-0403.txt
--- a/pep-0403.txt
+++ b/pep-0403.txt
@@ -392,7 +392,103 @@
    def f():
        ...
 
-   
+`goless <https://goless.readthedocs.org>`__ aims to bring support for
+"goroutine" style programming to Python, but some aspects currently need
+to be written out of order relative to their go counterparts. This PEP
+allows the "select" example from the goless documentation to be written as
+follows (assuming appropriate tweaks to some existing APIs, and an
+alternative ``switch`` API that is like ``select`` but expects the cases
+to be supplied as functions on a class)::
+
+    c1 = goless.chan()
+    c2 = goless.chan()
+
+    @in goless.go(func1)
+    def func1():
+        time.sleep(1)
+        c1.send('one')
+
+    @in goless.go(func2)
+    def func2():
+        time.sleep(2)
+        c2.send('two')
+
+    @in [goless.switch(cases) for i in range(2)]
+    class cases:
+        @goless.rcase(c1)
+        def chan1(chan, msg):
+            print("From channel 1:", msg)
+
+        @goless.rcase(c2)
+        def chan2(chan, msg):
+            print("From channel 2:", msg)
+
+        @goless.dcase()
+        def default(chan, msg):
+            print("From other channel:", msg)
+
+Now, that ``goless`` example could be written as follows today (again,
+assuming the addition of ``goless.switch`` and related changes)::
+
+    c1 = goless.chan()
+    c2 = goless.chan()
+
+    @goless.go
+    def func1():
+        time.sleep(1)
+        c1.send('one')
+
+    @goless.go
+    def func2():
+        time.sleep(2)
+        c2.send('two')
+
+    class cases:
+        @goless.rcase(c1)
+        def chan1(chan, msg):
+            print("From channel 1:", msg)
+
+        @goless.rcase(c2)
+        def chan2(chan, msg):
+            print("From channel 2:", msg)
+
+        @goless.dcase()
+        def default(chan, msg):
+            print("From other channel:", msg)
+
+    for i in range(2):
+        goless.switch(cases)
+
+The ``@in`` version helps make it clear that the ``goless.go`` calls have
+non-trivial side effects, as well as moving the ``switch`` call ahead
+of the definition of the cases. However, it cries out for something more
+readable, even if it's just syntactic sugar for an if-elif chain (as was
+considered as one of the options in PEP 3103). That might look something
+like::
+
+    for i in range(2):
+        switch goless.select() as chan, msg:
+          case chan is c1:
+            print("From channel 1:", msg)
+          case chan is c2:
+            print("From channel 2:", msg)
+          else:
+            print("From other channel:", msg)
+
+Rather than the current::
+
+    for i in range(2):
+        chan, msg = goless.select()
+        if chan is c1:
+            print("From channel 1:", msg)
+        elif chan is c2:
+            print("From channel 2:", msg)
+        else:
+            print("From other channel:", msg)
+
+(Note: the fact this doesn't appear to offer any particularly compelling
+improvements to goless code *does* count heavily against the proposal)
+
 
 Reference Implementation
 ========================

-- 
Repository URL: http://hg.python.org/peps