Re: [Haskell-cafe] Switching GHC Version
Thanks for suggestions. Having /usr/bin scripts seems to work for me, Although virthualenv looks promising for package dependency management. But when run virthualenv with --ghc=tarball, it creates copy of GHC suite inside a project whose size is about 700MB. On 2012/02/07, at 8:41, Brandon Allbery wrote: > On Mon, Feb 6, 2012 at 18:27, HASHIMOTO, Yusaku wrote: > Hi, I wrote a simple shell function for switching GHC version on the > system. It works only under Mac OSX, and only switch GHCs installed > via .pkg installers. It's useful to experiment newer features without > worrying breaking environment. > > FWIW I'd consider two alternatives: > > (1) forgo links entirely and use something like > http://modules.sourceforge.net/ to manage $PATH; > > (2) instead of using the bundled create-links, have the /usr/bin scripts > check a per-user symlink and fall back to a system one; running the select > script as root sets the system symlink, running as user sets the per-user > symlink. > > -- > brandon s allbery allber...@gmail.com > wandering unix systems administrator (available) (412) 475-9364 vm/sms > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Switching GHC Version
Hi, I wrote a simple shell function for switching GHC version on the
system. It works only under Mac OSX, and only switch GHCs installed
via .pkg installers. It's useful to experiment newer features without
worrying breaking environment.
GHC_BASE_DIR=/Library/Frameworks/GHC.framework/Versions/
ghcs () {
VERSION=$1
sudo $GHC_BASE_DIR/$VERSION/Tools/create-links . /Library/Frameworks /
}
Usage:
~/work/today 08:21 ghcs 7.4.0.20111219-x86_64
Password:
~/work/today 08:21 ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.4.0.20111219
~/work/today 08:21 ghcs 7.4.1-x86_64
~/work/today 08:22 ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.4.1
Now I'm curious of better way to achieve this. This have limitations
described above. Even it requires sudo because it modified symbolic
links under `/usr`.
Suggestions?
-nwn
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Re: [Haskell-cafe] Hierarchical tracing for debugging laziness
Great, It illustrates why difference lists are awesome.
import HTrace
app :: [a] -> [a] -> [a]
app [] ys = htrace "app" ys
app (x:xs) ys = htrace "app" (x:app xs ys)
rev1 [] = htrace "[]" []
rev1 (x:xs) = htrace "rev1" (app (rev1 xs) [x])
rev2 [] ys = htrace "ys" ys
rev2 (x:xs) ys = htrace ":" (rev2 xs (x:ys))
*Main> rev1 [1..10]
rev1
rev1
rev1
rev1
rev1
rev1
rev1
rev1
rev1
rev1
[]
app
app
app
app
app
app
app
app
app
app
[10app
app
app
app
app
app
app
app
app
,9app
app
app
app
app
app
app
app
,8app
app
app
app
app
app
app
,7app
app
app
app
app
app
,6app
app
app
app
app
,5app
app
app
app
,4app
app
app
,3app
app
,2app
,1]
*Main> rev2 [1..10]
:4:1:
No instance for (Show ([a0] -> [a0]))
arising from a use of `print'
Possible fix: add an instance declaration for (Show ([a0] -> [a0]))
In a stmt of an interactive GHCi command: print it
*Main> rev2 [1..10] []
:
:
:
:
:
:
:
:
:
:
ys
[10,9,8,7,6,5,4,3,2,1]
Thanks for sharing!
On 25 January 2012 01:47, Eugene Kirpichov wrote:
> Hi cafe,
>
> Look how one can watch the evaluation tree of a computation, to debug
> laziness-related problems.
>
> {-# LANGUAGE BangPatterns #-}
> module HTrace where
>
> import Data.List (foldl')
> import Data.IORef
> import System.IO.Unsafe
>
> level = unsafePerformIO $ newIORef 0
>
> htrace str x = unsafePerformIO $ do
> lvl <- readIORef level
> putStrLn (replicate (4*lvl) ' ' ++ str)
> writeIORef level (lvl+1)
> let !vx = x
> writeIORef level lvl
> return vx
>
> xs = map (\x -> htrace (show x) x) [1..10]
>
> s = foldl (\a b -> htrace "+" (a+b)) 0 xs
> s2 = foldl' (\a b -> htrace "+" (a+b)) 0 xs
>
> b = htrace "b" 2
> c = htrace "c" 3
> a = htrace "a" $ b + c
> x = htrace "x" $ b + c
>
> *HTrace> a
> a
> b
> c
> 5
> *HTrace> x
> x
> 5
>
> *HTrace> s
> +
> +
> +
> +
> +
> +
> +
> +
> +
> +
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
> 10
> 55
>
> (reload)
> *HTrace> s2
> +
> 1
> +
> 2
> +
> 3
> +
> 4
> +
> 5
> +
> 6
> +
> 7
> +
> 8
> +
> 9
> +
> 10
> 55
>
> --
> Eugene Kirpichov
> Principal Engineer, Mirantis Inc. http://www.mirantis.com/
> Editor, http://fprog.ru/
>
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Re: [Haskell-cafe] ANN: has-0.4 Entity based records
>> There are many libraries to write function "takes an record has Foo >> and Bar and returns something." But writing type of the function is >> still difficult. I can't write such types using HList or records >> without reading documents. I think, using has, There's few effort to >> write such types. > > In which manner do you need to read less documentation to write: > > ] f :: Has Foo r => r -> ... > > Instead when using HList: > > ] f :: HasField Foo record fieldType => ... HasField only gives projection function (hLookupByLabel), but Has gives projection, injection and modification function. If I want to write a generic function injecting a value into field Foo in a record by HList, I should read documentation more. >> I think `has' fits the needs of Haskellers who have the good habit of >> writing a type of a function before its definition. > > What does this mean exactly in terms of the type inference possible? Probably, yes. it's still fragile due to some reasons e.g. the behavior of UndecidableInstances language extension. > import Data.Has > data Foo = Foo; type instance TypeOf Foo = Int > data Bar = Bar; type instance TypeOf Bar = Int > f r = (Foo ^. r) + (Bar ^. r) *Main> :t f f :: forall s. (Contains (Labelled Foo Int) s, Contains (Labelled Bar Int) s) => s -> TypeOf Foo -nwn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: has-0.4 Entity based records
Sorry for spamming, what I wanted to write is I think `has' has better interface than other record packages in types. There are many libraries to write function "takes an record has Foo and Bar and returns something." But writing type of the function is still difficult. I can't write such types using HList or records without reading documents. I think, using has, There's few effort to write such types. I think `has' fits the needs of Haskellers who have the good habit of writing a type of a function before its definition. On 14 May 2010 07:58, HASHIMOTO, Yusaku wrote: > On 11 May 2010 03:25, adam vogt wrote: >> On Tue, May 4, 2010 at 12:18 PM, HASHIMOTO, Yusaku >> wrote: >>> This library is inspired by HList[2], and interfaces are stealed from >>> data-accessors[3]. And lenses[4], fclabels[5], and records[6] devote >>> themselves to similar purposes. >>> >>> [2]: http://hackage.haskell.org/package/HList >>> [3]: http://hackage.haskell.org/package/data-accessor >>> [4]: http://hackage.haskell.org/package/lenses >>> [5]: http://hackage.haskell.org/package/fclabels >>> [6]: http://hackage.haskell.org/package/records >>> >>> Enjoy! >>> >>> -nwn >> >> Which niche does `has' fit between extensible (and more complicated) >> records like HList and records vs the libraries that provide only >> accessors? > > You may find `has' useful when you want to use a label name in more > than one record structures. This is achieved by HList, records and > wreckage, But I think has at its interface. > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: has-0.4 Entity based records
On 11 May 2010 03:25, adam vogt wrote: > On Tue, May 4, 2010 at 12:18 PM, HASHIMOTO, Yusaku wrote: >> This library is inspired by HList[2], and interfaces are stealed from >> data-accessors[3]. And lenses[4], fclabels[5], and records[6] devote >> themselves to similar purposes. >> >> [2]: http://hackage.haskell.org/package/HList >> [3]: http://hackage.haskell.org/package/data-accessor >> [4]: http://hackage.haskell.org/package/lenses >> [5]: http://hackage.haskell.org/package/fclabels >> [6]: http://hackage.haskell.org/package/records >> >> Enjoy! >> >> -nwn > > Which niche does `has' fit between extensible (and more complicated) > records like HList and records vs the libraries that provide only > accessors? You may find `has' useful when you want to use a label name in more than one record structures. This is achieved by HList, records and wreckage, But I think has at its interface. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: has-0.4 Entity based records
I think I missed your point in my last post, and there are more
necessary extensions need to be enabled than I wrote before.
TypeFamilies, TypeOperator and FlexibleContexts extensions are
necessary. So you need to write this at top of the code if you don't
choose OPTIONS_GHC pragma.
> {-# LANGUAGE TypeFamilies,TypeOperators,FlexibleContexts #-}
Sorry for incorrect information.
-nwn
On 5 May 2010 02:33, HASHIMOTO, Yusaku wrote:
> I uploaded new version (0.4.0.1) of this package with proper pragmas.
>
> On 5 May 2010 02:00, HASHIMOTO, Yusaku wrote:
>> Hello
>>
>>>> I'm pleased to announce the release of my new library, named "has",
>>>> written to aim to ease pain at inconvinience of Haskell's build-in
>>>> records.
>>>
>>> Hmm, nice work, looks interesting.
>>
>> Thanks!
>>
>>>> You can use the has in three steps (without counting installation).
>>>>
>>>> 1. Write {-# OPTIONS_GHC -fglasgow-exts #-} top of your code,
>>>
>>> This is going out of style. It would be nice to know specifically
>>> what LANGUAGE extensions are necessary.
>>
>> Ah, yes. {-# LANGUAGE TypeFamilies #-} is enough for that literate
>> haskell file, But the has depends GHC's language extensions such as
>> UndecidableInstances, OverlappingInstances and TypeFamilies. But I'll
>> remove OPTIONS_GHC pragma from library codes. Thank you for your
>> suggestion.
>>
>> -nwn
>>
>
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Re: [Haskell-cafe] ANN: has-0.4 Entity based records
I uploaded new version (0.4.0.1) of this package with proper pragmas.
On 5 May 2010 02:00, HASHIMOTO, Yusaku wrote:
> Hello
>
>>> I'm pleased to announce the release of my new library, named "has",
>>> written to aim to ease pain at inconvinience of Haskell's build-in
>>> records.
>>
>> Hmm, nice work, looks interesting.
>
> Thanks!
>
>>> You can use the has in three steps (without counting installation).
>>>
>>> 1. Write {-# OPTIONS_GHC -fglasgow-exts #-} top of your code,
>>
>> This is going out of style. It would be nice to know specifically
>> what LANGUAGE extensions are necessary.
>
> Ah, yes. {-# LANGUAGE TypeFamilies #-} is enough for that literate
> haskell file, But the has depends GHC's language extensions such as
> UndecidableInstances, OverlappingInstances and TypeFamilies. But I'll
> remove OPTIONS_GHC pragma from library codes. Thank you for your
> suggestion.
>
> -nwn
>
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Re: [Haskell-cafe] ANN: has-0.4 Entity based records
Hello
>> I'm pleased to announce the release of my new library, named "has",
>> written to aim to ease pain at inconvinience of Haskell's build-in
>> records.
>
> Hmm, nice work, looks interesting.
Thanks!
>> You can use the has in three steps (without counting installation).
>>
>> 1. Write {-# OPTIONS_GHC -fglasgow-exts #-} top of your code,
>
> This is going out of style. It would be nice to know specifically
> what LANGUAGE extensions are necessary.
Ah, yes. {-# LANGUAGE TypeFamilies #-} is enough for that literate
haskell file, But the has depends GHC's language extensions such as
UndecidableInstances, OverlappingInstances and TypeFamilies. But I'll
remove OPTIONS_GHC pragma from library codes. Thank you for your
suggestion.
-nwn
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[Haskell-cafe] ANN: has-0.4 Entity based records
Hello,
I'm pleased to announce the release of my new library, named "has",
written to aim to ease pain at inconvinience of Haskell's build-in
records.
With the has, You can reuse accessors over records to write generic
function, combine records with another.
Repository is at GitHub: http://github.com/nonowarn/has
Uploaded on Hackage: http://hackage.haskell.org/package/has
So you can install this by "cabal install has"
You can use the has in three steps (without counting installation).
1. Write {-# OPTIONS_GHC -fglasgow-exts #-} top of your code,
import Data.Has module.
> {-# OPTIONS_GHC -fglasgow-exts #-}
> import Data.Has
2. Define entities. "Entity" is data to index field in records.
You can define an entity in one line.
> data Foo = Foo; type instance TypeOf Foo = Int
(I lied) Before semicolon, declares entity. After semicolon,
specifies the type to which the entity points.
Define some entities for later examples.
> data Bar = Bar; type instance TypeOf Bar = Double
> data Baz = Baz; type instance TypeOf Baz = String
> data Quux = Quux; type instance TypeOf Quux = Bool
3. Define Records by concatinating fields of entities.
> type MyRecord = FieldOf Foo :&: FieldOf Bar :&: FieldOf Baz
This is almost same as writing
< data MyRecord = MyRecord { foo :: Int
< , bar :: Double
< , baz :: String
< }
To construct a value of record, remove colons and replace entities
in record with values, and uncapitalize some words.
> aRecord :: MyRecord
> aRecord = fieldOf 42 & fieldOf 3.14 & fieldOf "string"
And you can play with it.
To read/write/modify a value of field in records, you can use
functions with names stealed from data-accessor. But uses value-level
entities instead of accessors.
< Foo ^. aRecord -- Reading
< Foo ^= 4649 $ aRecord-- Writing
< Foo ^: (*2) $ aRecord-- Modifying
If we have another record type contains Foo field, You can still
access the field in the same way.
> type AnotherRecord = FieldOf Bar :&: FieldOf Foo
> anotherRecord :: AnotherRecord
> anotherRecord = fieldOf 2.71 & fieldOf 31
< Foo ^. anotherRecord -- And this also works
Using these functions and Has constraint, You can write generic
functions over records.
> fooIsGreaterThan :: (Has Foo r) => r -> Int -> Bool
> fooIsGreaterThan r x = (Foo ^. r) > x
< aRecord `fooIsGreaterThan` 40 -- evaluated to True
< anotherRecord `fooIsGreaterThan` 40 -- evaluated To False
Even if you defined another record by combining records by (:&:), you
can still access the field, and apply to generic functions.
> type MoreRecord = FieldOf Baz :&: FieldOf Quux
> type CombinedRecord = AnotherRecord :&: MoreRecord
> combinedRecord :: CombinedRecord
> combinedRecord = (fieldOf 1.618 & fieldOf 39) & (fieldOf "sowaka" & fieldOf
> True)
>-- We can omit parentheses
>-- (even place parens anyware in record)
< combinedRecord `fooIsGreaterThan` 40 -- This yet works
The Has constraint provides not only genericity but also safety. If
the record doesn't satisfy the constraint, the type checker rejects
it.
> predicateOnRecords :: (Has Foo r, Has Quux r) => r -> Bool
> predicateOnRecords r = fooIsGreaterThan r 30 && (Quux ^. r)
< predicateOnRecords combinedRecord -- This is OK
< predicateOnRecords aRecord-- This yields compile error
More examples included in package[1]
[1]: http://github.com/nonowarn/has/tree/master/examples/
This library is inspired by HList[2], and interfaces are stealed from
data-accessors[3]. And lenses[4], fclabels[5], and records[6] devote
themselves to similar purposes.
[2]: http://hackage.haskell.org/package/HList
[3]: http://hackage.haskell.org/package/data-accessor
[4]: http://hackage.haskell.org/package/lenses
[5]: http://hackage.haskell.org/package/fclabels
[6]: http://hackage.haskell.org/package/records
Enjoy!
-nwn
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