Remember that there are two proposals here, one potentially to the Python team, one to the Haskell team . Of course the Haskell guys are strongly interested in the use case Dan describes -- mitigating risk by using Haskell for small components first, as part of larger legacy systems. The Python guys are more interested in Python use from Haskell, by the looks of it. -- Don westondan:
I notice that you omit from the advantages of calling Haskell from Python what I consider the most important reason of all (at least from the Haskell community side).
The choice of programming language (at least at the top level) is primarily a political or managerial choice, not a technical one. Python is not merely a "terrific glue language", it is often the "blessed" language, and currently the language of choice in some industries, including my own. This is not just "glue code" either: one in-house application has about 100,000 lines of Python code (calling a comparable amount of C++ code)!
Any hope of introducing Haskell into this realm requires a way to work Haskell in slowly and from the bottom. As such I view your proposed project as quite valuable, a robust and easy-to-use Python-Haskell bridge (Python on top) being essential to growing the presence of Haskell in non-academic circles.
Of course, it may be for this very political reason that you have omitted the above from your list, in which case I completely understand. :)
Dan
Michał Janeczek wrote:
Hi,
This is my second take on the project proposal. I have expanded on a few points, and hopefully also clarified a little bit.
Please comment :)
Regards, Michal
Python-Haskell bridge =====================
Description -----------
This project will seek to provide a comprehensive, high level (and thus easy to use) binding between Haskell and Python programming languages. This will allow using libraries of either side from each language.
If we decide to support function callbacks, these two functionalities (embedding Haskell in Python, and vice versa) become interrelated. In this light, it makes sense to implement them in the scope of the same project.
Advantages of calling Haskell from Python -----------------------------------------
* Robust components
It might be beneficial to implement safety-critical componenets in a strongly, statically typed language. Since Python itself is a terrific "glue language", such components would usually be purely functional, leaving IO to the Python side. Embedding Haskell code in this way is of particular interest when there already is a large existing Python infrastructure. One can implement new functionality in a form of Haskell plugin/component, even if complete rewrite is not feasible.
* Performance improvements for speed-critical code
Haskell compiled to native code is typically an order of magnitude faster than Python. Aside from that, advanced language features (such as multicore parallel runtime, very lightweight threads and software transactional memory) further serve to improve the performance. Haskell could become a safe, high level alternative to commonly used C extensions.
* Access to sophisticated libraries
While its set of libraries is not as comprehensive as that of Python, Haskell can still offer some well tested, efficient libraries. Some of the examples might be:
* rich parser combinator libraries (like Parsec) * persistent, functional data structures (i.e. Data.Map, Data.IntMap, Data.Sequence, Data.ByteString) * QuickCheck testing library to drive analysis of Python code
Advantages of calling Python from Haskell -----------------------------------------
* Python as a scripting language for Haskell applications
Python is widely considered to be more approachable for regular users. As such, it could be used as a configuration/extension language for applications that benefit from extra flexibility. One example of such application is xmonad window manager.
* Access to a large number of libraries
As a much more popular language, Python has built up an impressive suite of libraries. There already are Haskell projects which rely on Python code to implement missing functionality, for example a paste bin application hpaste, which uses Pygments syntax coloring library.
Deliverables ------------
* A low level library to access and manage Python objects from Haskell
* Library support for wrapping Haskell values in Python objects. This is necessary to allow function callbacks. In addition, thanks to that feature large and/or lazy data structures can be efficiently passed from Haskell to Python
* A set of low level functions to convert built-in data types between Haskell and Python (strings, numbers, lists, dictionaries, generators etc.)
* A high level wrapper library for Haskell that simplifies embedding and calling Python code
* A set of functions, and possibly a tool, to wrap up monomorphic functions and expose them to Python through foreign export facility
* A way (an external tool, or a Template Haskell macro) to easily derive conversion functions for user-defined data types/objects
* Documentation and a set of examples for all of above
Optional goals --------------
In order of increasing amount of work and decreasing priority:
* Exporting a wider class of functions to Python
* A Python module that inspects a compiled Haskell module and transparently exposes functions within. This might be possible thanks to GHC API _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
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