gmane.comp.lang.scala

sort on two keys

Mohamed Bana — 2010-02-09T21:05:41

Hi All,

What would be the equivalent of the C# program below?

var counts = new Dictionary<string, int>();

var sortedDict =
  from entry in counts
  orderby entry.Value descending, entry.Key ascending
  select entry;

that is, sort by max no. then alphabetically.

—Mohamed

Very weird error

David Pollak — 2010-02-09T00:44:47

Adding ARM to Scala's standard library

Blair Zajac — 2010-02-08T16:06:41

Probably anybody that has written something that needs to be closed after use 
has written something like

object With
{
   def closeable[C <: java.io.Closeable,R](c: C)
                                          (f: C => R): R =
   {
     try {
       f(c)
     }
     finally {
       try {
        c.close()
       }
       catch {
         // #### Log this, but how?
         case e =>
       }
     }
   }
}

Then it would be used as

With.closeable(new ByteArrayOutputStream(1024)) { os =>
   ...
}

This looks like something that would do well in Scala's standard library.

One question is how to deal with the logger for the standard library.  I use 
slf4j in my projects but not everybody does.  I think if this code is in the 
standard library then it must provide a way to have the exception from #close() 
be logged with the logger of choice.  The With object could become an abstract 
class with an abstract logging method than projects would instantiate their own 
concrete class with their logger of choice.

Compiler crash

ratiud — 2010-02-07T18:25:32

Hi,

I am using the Scala nightly build (from eclipse) and when entering this
code:

{{{
scala> for (k <- 0 until xs.xize)
for(i = 0 until (xs.size)) {

}
}}}

the compiler crashes with the folowing message:

  | <console>:2: error: '<-' expected but '=' found.
       for(i = 0 until (xs.size)) {
                              ^
Exception in thread "main" java.lang.UnsupportedOperationException:
Position.point
at scala.tools.nsc.util.Position$class.point(Position.scala:89)
at scala.tools.nsc.util.NoPosition$.point(Position.scala:194)
at scala.tools.nsc.util.Position$class.endOrPoint(Position.scala:98)
at scala.tools.nsc.util.NoPosition$.endOrPoint(Position.scala:194)
at
scala.tools.nsc.ast.parser.TreeBuilder.closurePos$1(TreeBuilder.scala:365)
at scala.tools.nsc.ast.parser.TreeBuilder.makeFor(TreeBuilder.scala:370)
at scala.tools.nsc.ast.parser.TreeBuilder.makeFor(TreeBuilder.scala:403)
at scala.tools.nsc.ast.parser.Parsers$Parser.expr0(Parsers.scala:1054)
at scala.tools.nsc.ast.parser.Pa

regex and unicode

TuX RaceR — 2010-02-07T09:03:42

Hello Scala List,

I am trying to tokenize using a regex phrases in languages not written 
with ASCII only  (and I do not speak about a Chinese or Japanese 
tokenizer ;) ) and I cannot make it work:

scala> val text="Cet été là"                                
text: java.lang.String = Cet été là

scala> """(?iu)(\w+)""".r.findAllIn( text ).foreach(println)
Cet
t
l

scala> """(?i)(\w+)""".r.findAllIn( text ).foreach(println)
Cet
t
l

scala> """(?i)(.+)""".r.findAllIn( text ).foreach(println)
Cet été là

I saw the (?u) modifier that should match unicode but...
I am probably missing something but what ;) ?

Thanks
TuX

Compiler crash with -Yspezialize

Andreas Flierl — 2010-02-05T21:42:20

Hi there,

compiling this seemlingly simple code fragment:

import scala.collection.mutable.HashSet

object Excerpt {
  def main(args: Array[String]): Unit = {
    val nums = HashSet.empty[Int]
    for (a <- 1 to 10; b <- 1 to 10) {
      nums += (a * b)
    }
  }
}

with 
scalac-2.8 -Yspecialize Excerpt.scala
(using scala 2.8.0.Beta1 on Mac OS X)

produces the following, rather lengthy result:

exception when typing nums.+=
illegal cyclic reference involving class HashSet in file Excerpt.scala
scala.tools.nsc.symtab.Symbols$CyclicReference: illegal cyclic reference involving class HashSet
at scala.tools.nsc.symtab.Symbols$TypeSymbol.tpe(Symbols.scala:1810)
at scala.tools.nsc.symtab.Symbols$ClassSymbol.typeOfThis(Symbols.scala:1993)
at scala.tools.nsc.symtab.Types$ThisType.underlying(Types.scala:1026)
at scala.tools.nsc.symtab.Types$SimpleTypeProxy$class.isHigherKinded(Types.scala:173)
at scala.tools.nsc.symtab.Types$SingletonType.isHigherKinded(Types.scala:949)
at scala.tools.nsc.transform.UnCurry.sca

2.8, type parameters, manifests and traits

David Pollak — 2010-02-05T01:25:30

Howdy,

In 2.8, is it possible to have the manifest for a type parameter defined on
a trait reified someplace that's accessible to the trait.  The following
works with classes:

class Foo[T: Manifest] {
  def myType(implicit man: Manifest[T]): Manifest[T] = man
}

But it seems that because traits don't take parameters, you can't do trait
Foo[T: Manifest] ....

It would be very, very helpful to have a reification of trait type
parameters.  Any ideas on how this could be done?

Thanks,

David

New draft paper on unique references and Scala compiler plug-in

Philipp Haller — 2010-02-04T17:56:38

Hi all,

I'd like to announce a new draft paper on unique references.

   Title:   Capabilities for Uniqueness and Borrowing

   Authors: Philipp Haller and Martin Odersky

   Abstract:
   An important application of unique object references is safe and
   efficient message passing in concurrent object-oriented programming.
   However, to prevent the ill effects of aliasing, practical systems
   often severely restrict the shape of messages passed by reference.
   Moreover, the problematic interplay between destructive reads--often
   used to implement unique references--and temporary aliasing through
   ``borrowed'' references is exacerbated in a concurrent setting,
   increasing the potential for unpredictable run-time errors.

   This paper introduces a new approach to uniqueness. The idea is to use
   capabilities for enforcing both at-most-once consumption of unique
   references, and a flexible notion of uniqueness. The main novelty of
   our approach is a model of uniqueness and borrowing based on sim

scala source code formatter

michael hohn — 2010-02-04T06:36:51

Hi,

I've been editing scala (2.8) using emacs and eclipse recently, and
their formatting is inconsistent (which is ok).  But for collaboration
with others, especially using git, introducing superficial whitespace
changes is a really big problem.

Is there a standalone scala code formatter that I could run before
checking in code and that would enforce a particular format, much like
'indent' does for C?

Cheers,
Mike

Compiler Bug: Exponential bytecode generation from extractors

brian heylin — 2010-02-03T16:22:18

I've just been bitten by this bug:

https://lampsvn.epfl.ch/trac/scala/ticket/1133

Which in my case crashed the compiler (2.7.7). Is there any schedule for
this bug being fixed I wonder?

[ANN] configgy 1.5

Robey Pointer — 2010-02-02T23:08:31

Configgy is a library for handling config files and logging for a scala
daemon. The idea is that it should be simple and straightforward, allowing you
to plug it in and get started quickly, writing small useful daemons without
entering the shadowy world of java frameworks.


Changes in version 1.5 include these features:

  - ScribeHandler for sending log entries to a scribe server
  - ThrottledLogger for squelching repetitive messages
  - ConfigMap.toConfigString() will generate a config file as a string
  - Config.fromString() will parse a string into a Config object
  - command-line "-D" options can override/append config items
  - no longer squash all config keys to lowercase

and these bug fixes:

  - possible NPE in Logger.elements [ijuma]
  - various timezone bugs in tests
  - be less aggressive about clearing out log nodes


It can't be a project without a website, so that's here:

  http://www.lag.net/configgy/

The github repository is here:

  http://github.com/robey/configgy/tree/master

And, fo

overwrite mutators/accessors

Jochen Mader — 2010-02-02T14:38:37

Being a scala newbie I have a little problem understanding mutators.
Doing the following:

class Example {
   var exampleVar = 1
}

Will give me an integer property, the accessor 'exampleVar' and the mutator
'exampleVar_='.
I need to do some checks on the values that are set to exampleVar so I want
to overwrite the mutator.
Doing:

class Example {
   var exampleVar = 1
   def exampleVar_=(exampleVar: Int) {
     ....
   }
}

will give me a "ambiguous reference to overloaded definition". The examples
I found always use a private var and a def to achieve this.
Why is this? Is there no way to overwrite the default mutators/accessors?

Thx,

Jochen

Deadline Extended to Feb. 15: IEEE Software Multi-Paradigm Programming Special Issue - Sep/Oct 2010

Dean Wampler — 2010-02-02T04:35:59

Hi,

Sorry for the repeat emails. We have extended the deadline for submissions
for this special issue. It is now February 15th. If you thought about
submitting a paper, but didn't think you could make the original deadline,
we hope you will reconsider.

http://www.computer.org/portal/web/computingnow/swcfp5

Yours,
dean

Dean Wampler, Ph.D.
dean< at >polyglotprogramming.com

co-author: "Programming Scala", O'Reilly:
 - http://programmingscala.com

Nightly build logs page nonfunctional

Bill Burdick — 2010-02-01T08:51:09

I'm not sure whether this is intensional or not, but this has been
nonfunctional for a while:
http://scala-webapps.epfl.ch/hudson/view/Nightly/job/scala-nightly-main/  If
it's intentional, maybe the "nightly build logs" link should be taken out of
the "Nightly builds" section on the download page.


Bill

Possible bug in typechecker

Ben Hutchison — 2010-02-01T04:47:39

For a fortnight I have been dogged by compiler typecheck errors in
code that I think is correct. I have narrowed down a small test case,
which I believe should typecheck, that illustrates the problem.

Either (a) would someone please explain why this isnt typesafe (and
ideally how to correct it), or (b) should I report this in trac?

trait Dimension {
type ContainerType <: Container[X] forSome {type X <: Dimension}
}
object D1 extends Dimension {
type ContainerType = Container[D1.type]
}
class Container[D <: Dimension] {
def op(c: Container[D])
}
abstract class Context[Dim <: Dimension] {
val c1: Dim#ContainerType
val c2: Dim#ContainerType

/*
[error]  found   : Dim#ContainerType
[error]  required: Container[X] where type X <: Dimension
[error]         def test() = c1.op(c2)
[error]                            ^
*/
def test() = c1.op(c2)
}

Bug in scala 2.8.0 eclipse plugin preferences - Screen shot 2010-01-#70733D.png (1/1)

Claudio Nieder — 2010-01-31T15:25:02

Hi,

after uninstalling my previous scala plugin (2.7.x) I have installed the 
2.8 beta from 
http://www.scala-lang.org/scala-eclipse-plugin-beta-preview update site.

The installed version is 2.8.0.r20671-b20100126115340.

If I open Preferences->Scala Editor Preferences I see an empty field as 
shown in the attached screenshot.

This is with an eclipse 3.5.1 M20090917-0800 on Mac OS X 10.6.2.

claudio

Position.longString() does not honour tabulator characters

Alexander Berger — 2010-01-30T17:59:00

I suggest the following modification to trait "scala.util.parsing.input.Position"

  def longString = lineContents+"\n"+(" " * (column - 1))+"^"

should become

  def longString = lineContents+"\n"+lineContents.take(column-1).map{x => if (x == '\t') x else ' ' } + "^"

Using trait Position's longString method for error reporting it often happens that the caret (^) is (visually) at the wrong 
position if lineContents contains one or more tabulator characters.

Scala vs. X10

Marius Danciu — 2010-01-30T17:16:06

Hi all,

Did anyone look into X10 language? ... many things in there are very
Scala-ish but I wonder if anyone used it and perhaps share the experience?

Br's,
Marius

Scala coding guidelines needed? NOT formatting style!

jonathan mawson — 2010-01-28T14:38:33

I'm learning Scala and I'm *very* impressed. At first it looked like a
kitchen sink language, but now I see it's anything but that - the chosen
features fit together very well so that they multiplicative rather than
additive. Really excellent, profound well-thought out design. I did have a
"Hmmm, it's a pity that.." list. Then I looked at the spec for 2.8 and found
that the whole list had been take care of.

But - isn't it time for some coding style guidelines? I don't mean the
trivial stuff that emacs can hack, like function names and how many spaces
to a tab, but when to use an Array and when a List, when pattern matching to
get the value from an Option and when a HOF. What features tend to make code
slow and by how much? Where the gotchas? More importantly, what are the
questions that I don't know enough to ask, but really should? A lightweight
version of "Effective C++/Java/Perl/Whathaveyou", is what I'm suggesting, I
suppose.

It might help a lot if guidance like this evolved now - it could be the best

Yet another Scala Blog

ilangostl — 2010-01-27T23:10:00

Here is Yet another Scala blog that I started a few months ago.

http://scalatechnology.blogspot.com/

enjoy!

Ilango

Building scala with a lower Tuple/Product/Function size limit

Arthur Peters — 2010-01-27T22:05:04

I'm trying to use scala to program Mindstorm robots (the NXT brick) via
LeJOS [1]. But the LeJOS "linker" (it reduces and converts the byte code for
execution on the little system) does not support function with more than 16
parameters so Tuple16 and up cause problems.

What would I have to change to build a Scala environment with only
Tuple/Product/Function up to say 13?

I have tried it by changing the constants in: genprod.scala and
scala/tools/nsc/symtab/Definitions.scala and removing some classes from
AbstractFunction0.scala. However I get an error as follows when I build it:

[scalacfork] scala.tools.nsc.MissingRequirementError: class scala.Function14
not found.
[scalacfork]     at
scala.tools.nsc.symtab.Definitions$definitions$.getModuleOrClass(Definitions.scala:514)
[scalacfork]     at
scala.tools.nsc.symtab.Definitions$definitions$.getClass(Definitions.scala:472)
[scalacfork]     at
scala.tools.nsc.symtab.Definitions$definitions$$anonfun$1.apply(Definitions.scala:265)
[scalacfork]     at
scala.tools