The Mercury Programming Language | Hacker News Reader

The Mercury Programming Language

mercury.csse.unimelb.edu.au

20 pointsswannodette9 comments

Even if you don't find a way to use anything out of the functional-logical space, reading about languages like this can change the way you program when you are in a functional-only or logical-only language.

Here's a little oversimplification that I've found useful for understanding this stuff.

    * Mercury is the Haskell of Prolog
    * Curry is the Prolog of Haskell

It's interesting to see a lot of the ideas in Mercury addressed from the opposite direction Curry. See for yourself: http://www-ps.informatik.uni-kiel.de/currywiki/

This is how I feel about it. Mercury is an elegant language but I think the applicable domain is restricted to a very narrow subset of the industry. As a [primarily] web programmer I will generally only become more "cultured" by studying esoteric languages (Scheme, Haskell, Mercury, Curry) - that acculturation does diffuse into my day-to-day practice, though. I find myself structuring code in a novel manner (often times it's more clean, cogent, and effective too) that I would not normally have done with my narrower knowledge space, pre-saturation. I also see myself creating logic and using data structures that weren't historically typical of me.

I think every programmer should study esoteric languages. It's akin to the contrast of arithmetic and mathematical logic - you have the opportunity to appreciate and experience the ideal rather than the mundane. Not that beauty can't be found in building a web application (or any other application for that matter) using a framework and one's own set of libraries; I do everyday because I pour the expression of who I am into my practice - the thing is, it's [esoteric languages] the same sort of joy one derives from contemplating deep philosophical questions or from deliberately cultivating character through introspection.

I felt like whipping out the PhilosoRaptor tonight I guess...

The fact that people write tediously comprehensive imperative unit tests to verify their programs should be a warning sign that the use cases for logic programming may be more much general than you think. A hunch, nothing more. I'm just starting to dig into this stuff.

This!

People are itching for declarative testing systems. Writing testing code by hand is tedious and error-prone. Static typing works for a lot of things, but isn't completely satisfactory. Randomized testing is also useful (give a function that tests a property, give random_int -> value generators for its arguments, let it find edge cases), but those are only two facets of a much bigger picture.

I'm really interested in more modern takes on Prolog, but from what I've read about Mercury, it seems to throw out my favorite aspect: computing with partial information. Constraint logic programming seems like a more valuable direction, though I see the appeal in a Prolog-esque language informed by modern type theory, and I'm particularly interested in what it does with linear types.

I've always found this language interesting, especially because of its early commercial usage, but I haven't seen many first hand accounts of its use. Anyone care to chime in?

Prince XML is written in Mercury

http://en.wikipedia.org/wiki/Prince_XML

    Logic programming languages [...] have not had 
    significant impact on the computer industry.

    Mercury is a new logic/functional programming language

Mercury is "new" and admittedly interesting since 15 years now. Please somebody update the blurb.

If anyone running that site reads this, request: put a Hello World code sample right smack on the home page. Seeing the size and structure of the syntax to accomplish that basic task will tell me loads, immediately, in very little space, about your language. I can then dig in deeper, or move on, depending on interest.

To save others the effort, I did some spelunking and found a Hello World in a tutorial. Here it is:

  :- module hello.
  :- interface.
  :- import_module io.
  :- pred main(io::di, io::uo) is det.
  :- implementation.

  main(IOState_in, IOState_out) :-
    io.write_string("Hello, World!\n", IOState_in, IOState_out).

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