msgpack: haskell & python

Question

I'm confused by the differences between haskell and python clients for msgpack. This:

import Data.MessagePack as MP
import Data.ByteString.Lazy as BL

BL.writeFile "test_haskell" $ MP.pack (0, 2, 28, ())

and this:

import msgpack

with open("test_python", "w") as f:
    f.write(msgpack.packb([0, 2, 28, []]))

give me the different files:

$ diff test_haskell test_python
Binary files test_haskell and test_python differ

Can anybody explain, what I'm doing wrong? Maybe I misunderstood something about ByteString usage?

Does msgpack care about lists vs tuples? In haskell you're using a tuple (whose last element is unit aka `()`), and in python you're using a list (whose last element is `[]`, the empty list). Try [using python tuples](http://www.tutorialspoint.com/python/python_tuples.htm). — rampion, Sep 20 '14 at 15:47
@rampion Result of the python ``packb`` with tuples is the same as for lists. — erthalion, Sep 20 '14 at 15:53

score 9 · Accepted Answer · edited Apr 10 '16 at 18:04

9

The empty tuple () in Haskell is not like empty tuple or empty list in Python. It's similar to None in Python. (in the context of msgpack).

So to get the same result, change the haskell program as:

MP.pack (0, 2, 28, [])  -- empty list

Or change the python program as:

f.write(msgpack.packb([0, 2, 28, None]))

edited Apr 10 '16 at 18:04

xiº

answered Sep 20 '14 at 16:19

falsetru

1 Answers1