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218 :: Maybe there's a template or macro that could achieve this?

• MFlamer (orginal) [2013-09-01T02:40:35+02:00] view original

  I'm experimenting with writing a library of functional structures and combinators for use with Nimrod and to help me learn the language. I mentioned in another post that I want to create type classes for functors and monads eventually, this might be possible with the user defined type classes that are coming soon, or maybe not. I tried to implement them in Rust and the lack of higher kinded types made it too clumsy to be worth it, we'll see. Anyway, for now I'm starting with some simpler concepts like function composition and partial application. My attempts at this have worked well and are in this gist, take a look if you want https://gist.github.com/mflamer/6401476.

  With partial application and composition you can do cool things like this,

  proc sum(x:int, y:int):int = x + y proc double(x:int):int = 2 * x var doubleSum10 = double & sum$|10 echo(doubleSum10(5)) # 30

  Obviously a trivial example, but when you start to think of the function(procedure) as the primary unit of abstraction, it can get powerful and these are the basic building blocks.

  My question is.. I don't have much experience with macros and have the feeling that my partial application operators could have been defined using one. I haven't figured out how to make it work yet. Anyone want to take a stab at it? Thanks.

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• Araq (orginal) [2013-09-01T09:15:01+02:00] view original

  My question is.. I don't have much experience with macros and have the feeling that my partial application operators could have been defined using one. I haven't figured out how to make it work yet. Anyone want to take a stab at it? Thanks.

  It's been a while since I last thought about it, but in general macros will be up for tasks like this once a type API for them arrives. (I am currently reworking the whole evaluation engine that is used to evaluate macros...)

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• MFlamer (orginal) [2013-09-01T09:35:53+02:00] view original

  I was thinking I could use the newProc() in the macros API and fill it with the supplied arguments and somehow make the body the original call, returning a new proc expecting the remaining arguments. Does that make any sense?

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• MFlamer (orginal) [2013-09-01T10:22:05+02:00] view original

  What should the parameters to this procedure look like?

  proc params=(someProc: PNimrodNode; params: PNimrodNode) {.compileTime, raises: [EInvalidValue], tags: [].}

  I can create a new proc like this

  macro curry(f:expr, args:varargs[expr]):expr =

  result.add(newProc(body = newStmtList(newCall(f,args), args)))

  but I'm not clear how to add the parameters that this new proc is going to expect.

  This macro system seems really exciting and powerful. Thanks!

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• zahary (orginal) [2013-09-01T12:01:59+02:00] view original

  You may want to take a look at this:

  https://github.com/Araq/Nimrod/issues/402

  Indeed, the missing part of the puzzle for implementing this solution is an "arity" type trait for procs.

  Implementing type traits is extremely simple. There is only one function in the compiler that has to be modified:

  https://github.com/Araq/Nimrod/blob/master/compiler/evals.nim#L907

  and then the type trait has to be exported here:

  https://github.com/Araq/Nimrod/blob/master/lib/pure/typetraits.nim

  If you like to get your hands dirty, we'd love to accept patches for richer type APIs, but otherwise I could just go ahead and implement the arity type trait that is needed here.

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• MFlamer (orginal) [2013-09-01T18:25:25+02:00] view original

  Thanks for the hint zahary. I'll take a look and see what I can come up with.

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• MFlamer (orginal) [2013-09-02T08:37:45+02:00] view original

  I've posted the proposed change here https://gist.github.com/mflamer/6409814. It builds but I'm not entirely sure how to use it and have doubts if it will work.

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• MFlamer (orginal) [2013-09-02T22:58:52+02:00] view original

  zahary, I've got the "arity" proc working now. Did you imagine curry being a proc, template or macro?

  My thought is to create a macro that returns a lambda. I think I can make this work......

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