Re: [GHC] #3843: Merge plugins into HEAD
#3843: Merge plugins into HEAD -+-- Reporter: dreixel |Owner: simonpj Type: task | Status: new Priority: normal|Milestone: 7.2.1 Component: Compiler | Version: 6.13 Keywords:| Testcase: Blockedby:| Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: None/Unknown -+-- Comment(by simonpj): I'm not sure what support for home-package plugins is. I certainly simplified the patch when testing it; I removed several small modules, eliminated unnecessary module loops; simplified data types. But I didn't know that I had removed any functionality. If so, apologies. Happy to discuss. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3843#comment:31 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
[GHC] #5290: Add UNPACK support to Template Haskell
#5290: Add UNPACK support to Template Haskell
---+
Reporter: mikhail.vorozhtsov | Owner:
Type: feature request | Status: new
Priority: normal | Component: Template Haskell
Version: 7.1 |Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple|Blocking:
Architecture: Unknown/Multiple| Failure: None/Unknown
---+
I've just hacked it in:
{{{
$ ghci -XTemplateHaskell
GHCi, version 7.1.20110630: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
λ import Language.Haskell.TH
λ runQ [d| data T = T {-# UNPACK #-} !Int |]
Loading package array-0.3.0.2 ... linking ... done.
Loading package containers-0.4.0.0 ... linking ... done.
Loading package pretty-1.0.2.0 ... linking ... done.
Loading package template-haskell ... linking ... done.
[DataD [] T [] [NormalC T [(Unpacked,ConT GHC.Types.Int)]] []]
λ
}}}
TH.hs:
{{{
{-# LANGUAGE TemplateHaskell #-}
module TH where
import Language.Haskell.TH
d :: Q [Dec]
d = return [DataD [] n [] [NormalC n [(Unpacked,ConT ''Int)]] []]
where n = mkName T
}}}
Main.hs:
{{{
{-# LANGUAGE TemplateHaskell #-}
import TH
$(d)
instance Show T where
show (T i) = show i
main = putStrLn $ show (T 10)
}}}
Compiling and running:
{{{
$ ghc -ddump-splices -fforce-recomp Main.hs
[1 of 2] Compiling TH ( TH.hs, TH.o )
[2 of 2] Compiling Main ( Main.hs, Main.o )
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
Loading package pretty-1.0.2.0 ... linking ... done.
Loading package array-0.3.0.2 ... linking ... done.
Loading package containers-0.4.0.0 ... linking ... done.
Loading package template-haskell ... linking ... done.
Main.hs:1:1: Splicing declarations
d
==
Main.hs:5:3
data T = T {-# UNPACK #-} !Int
Linking Main ...
$ ./Main
10
}}}
Please consider merging.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5290
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Re: [GHC] #5288: Less noisy version of -fwarn-name-shadowing
#5288: Less noisy version of -fwarn-name-shadowing -+-- Reporter: batterseapower| Owner: Type: feature request | Status: new Priority: normal| Component: Compiler Version: 7.0.3 |Keywords: Testcase:| Blockedby: Os: Unknown/Multiple |Blocking: Architecture: Unknown/Multiple | Failure: None/Unknown -+-- Changes (by malcolm.wallace@…): * cc: malcolm.wallace@… (added) -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5288#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #4359: Implement lambda-case/lambda-if
#4359: Implement lambda-case/lambda-if
-+--
Reporter: batterseapower|Owner: igloo
Type: feature request | Status: patch
Priority: high |Milestone: 7.4.1
Component: Compiler | Version: 7.1
Keywords:| Testcase:
Blockedby:| Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
-+--
Comment(by simonpj):
Thanks for rebasing. The only issue here is one of syntax. Several
people have expressed anxiety about making so quiet a symbol as \ into a
layout herald, and have showed that some existing code might break.
So, what to do? One possibility is ''not'' to make \ into a symbol
introducing ''implicit'' layout, but still to allow ''explicit'' layout
with braces and semi-colons. Thus:
{{{
\ { True - e1; False - e2 }
}}}
would be ok. But this would not be ok
{{{
\ True - e1
False - e2
}}}
That seems like a reasonable compromise. Using the brace/semicolon stuff
is compatible with the way case expressions work, which is a Good Thing.
Any comments?
Simon
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4359#comment:48
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Re: [GHC] #5019: OS X: ld: warning: could not create compact unwind for _ffi_call_unix64
#5019: OS X: ld: warning: could not create compact unwind for _ffi_call_unix64
---+
Reporter: altaic |Owner: igloo
Type: bug | Status: new
Priority: normal |Milestone: 7.2.1
Component: Compiler| Version: 7.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: MacOS X | Blocking:
Architecture: x86_64 (amd64) | Failure: Incorrect warning at
compile-time
---+
Comment(by batterseapower):
After I installed XCode4 I started getting lots of instances of this
error:
{{{
ld: warning: could not create compact unwind for .LFB3: non-standard
register 5 being saved in prolog
}}}
A validate run fails with:
{{{
Unexpected failures:
cabal/cabal01 cabal01 [bad stderr] (normal)
cabal/cabal04 cabal04 [bad stderr] (normal)
codeGen/should_compile 2578 [bad stderr] (normal)
driver driver062a [bad stderr] (normal)
driver driver062b [bad stderr] (normal)
driver driver062c [bad stderr] (normal)
driver driver062d [bad stderr] (normal)
driver driver062e [bad stderr] (normal)
driver driver081a [bad stderr] (normal)
driver driver081b [bad stderr] (normal)
driver rtsopts001 [bad stderr] (normal)
driver rtsopts002 [bad stderr] (normal)
driver withRtsOpts [bad stderr] (normal)
driver/1372 1372 [bad stderr] (normal)
driver/1959 1959 [bad stderr] (normal)
driver/T3007T3007 [bad stderr] (normal)
driver/recomp004recomp004 [bad stderr] (normal)
gadtgadt23 [bad stderr] (normal)
lib/IO 3307 [bad stderr] (normal)
lib/IO T4113 [bad stdout] (normal)
lib/IO environment001 [bad stderr] (normal)
module mod179 [stderr mismatch] (normal)
perf/compiler T4801 [stat not good enough] (normal)
perf/should_run T2902 [bad stderr] (normal)
perf/should_run T3736 [bad stderr] (normal)
programs/hs-booths-boot [stderr mismatch] (normal)
rename/prog006 rn.prog006 [bad stderr] (normal)
rts 4850 [bad stderr] (normal)
rts T4059 [bad stderr] (normal)
typecheck/bug1465 bug1465 [bad stderr] (normal)
}}}
These are almost all failing because of the extra warning text.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5019#comment:11
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Re: [GHC] #3843: Merge plugins into HEAD
#3843: Merge plugins into HEAD
-+--
Reporter: dreixel |Owner: simonpj
Type: task | Status: new
Priority: normal|Milestone: 7.2.1
Component: Compiler | Version: 6.13
Keywords:| Testcase:
Blockedby:| Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
-+--
Comment(by batterseapower):
simon: I've restored the home-package plugin support. This is basically
just the ability to write:
{{{
{-# OPTIONS_GHC -fplugin Foo #-}
module Bar
...
}}}
And then if you use ghc --make on Bar.hs Foo.hs, will be compiled if is
not already. Have a look at e49dae36a00b2af8f6ad583dd24f9bacf5711242 if
you want to see what is required.
~~~
thoughtpolice: As I thought, linking is not working properly: see the
newly-commited test plugins06. In this test, the plugin seqs the static
flags, which provokes the error:
{{{
ghc-stage2: panic! (the 'impossible' happened)
(GHC version 7.1.20110630 for i386-apple-darwin):
Static flags have not been initialised!
Please call GHC.newSession or GHC.parseStaticFlags early enough.
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
}}}
This is because a new instance of the GHC package has been loaded, which
does not have its staticFlags initialised since it does not share state
with the initial copy.
The fix is to do export-dynamic and change Linker.hs to get ghc package
symbols from the current executable (which is what I did in my original
patch), or use dynamic linking for the ghc package in which case
everything will work.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3843#comment:32
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Re: [GHC] #4359: Implement lambda-case/lambda-if
#4359: Implement lambda-case/lambda-if
-+--
Reporter: batterseapower|Owner: igloo
Type: feature request | Status: patch
Priority: high |Milestone: 7.4.1
Component: Compiler | Version: 7.1
Keywords:| Testcase:
Blockedby:| Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
-+--
Comment(by mikhail.vorozhtsov):
Replying to [comment:48 simonpj]:
Thus:
{{{
\ { True - e1; False - e2 }
}}}
would be ok. But this would not be ok
{{{
\ True - e1
False - e2
}}}
That seems like a reasonable compromise. Using the brace/semicolon
stuff is compatible with the way case expressions work, which is a Good
Thing. Any comments?
Ugh. This is getting uglier and uglier. I've been using the current
version of the patch for some time and I think the syntax has two major
problems:
1. It rejects the nice-looking indentation we are all used to in the
single-clause case (see my 'mask' example above).
2. It looks like a case expression, but has different pattern syntax, i.e.
I constantly write
{{{
foo = \
Nothing - ...
Just a - ...
}}}
instead of the correct
{{{
foo = \
Nothing - ...
(Just a) - ...
}}}
Explicit layout solves the first issue, IMO, at the expense of graphic
clarity. I mean
{{{
foo = \
{ Nothing - do
abc
def
; (Just a) - do
abc
def
}
}}}
just makes my eyes hurt. Do we really want a feature that is only
accessible using explicit layout?
I think the fact that single- and multi-clause lambdas require different
indentation rules (and we can't look ahead to distinguish them) tells us
to use a different token (\fn, \fun, \let?). I'd also say that {{{\x -
case x of ...}}} (or {{{x - foo; case x of ...}}}) is such a common idiom
that it deserves its anonymous counterpart (with respect to pattern
syntax) regardless of the whole multi-clause lambda thing.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4359#comment:49
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Re: [GHC] #4359: Implement lambda-case/lambda-if
#4359: Implement lambda-case/lambda-if -+-- Reporter: batterseapower|Owner: igloo Type: feature request | Status: patch Priority: high |Milestone: 7.4.1 Component: Compiler | Version: 7.1 Keywords:| Testcase: Blockedby:| Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: None/Unknown -+-- Comment(by simonpj): Concerning (1) I don't understand. If you don't put a curly brace, everything would happen just like now... so `mask` would be fine. Concerning (2), yes, I am suggesting that this feature is only accessible using explicit layout. It's not perfect, but the alternatives seem worse to me. Does anyone else have other ''concrete'' proposals? If so, let's hear them. The default alternative is to do nothing. Simon -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4359#comment:50 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3843: Merge plugins into HEAD
#3843: Merge plugins into HEAD -+-- Reporter: dreixel |Owner: simonpj Type: task | Status: new Priority: normal|Milestone: 7.2.1 Component: Compiler | Version: 6.13 Keywords:| Testcase: Blockedby:| Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: None/Unknown -+-- Comment(by simonpj): Great. If you two work it out, let me know what to commit. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3843#comment:33 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #4359: Implement lambda-case/lambda-if
#4359: Implement lambda-case/lambda-if
-+--
Reporter: batterseapower|Owner: igloo
Type: feature request | Status: patch
Priority: high |Milestone: 7.4.1
Component: Compiler | Version: 7.1
Keywords:| Testcase:
Blockedby:| Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
-+--
Comment(by mikhail.vorozhtsov):
Replying to [comment:50 simonpj]:
Concerning (1) I don't understand. If you don't put a curly brace,
everything would happen just like now... so `mask` would be fine.
Yes. I was referring to the syntax implemented in the patch.
Does anyone else have other ''concrete'' proposals? If so, let's hear
them.
Let me bug you one last time. Please consider adding \case expressions
''in addition'' to multi-clause lambdas. Сase expressions are at the
fingertips of every haskeller, not having their anonymous version will
(and in my case already is) lead to constant stumbling (due to different
pattern syntax). Besides, we already have that sort of duplication for
one-argument named functions ({{{fun P = ...}}} vs {{{fun x = case x of P
- ...}}}).
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4359#comment:51
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Re: [GHC] #4359: Implement lambda-case/lambda-if
#4359: Implement lambda-case/lambda-if -+-- Reporter: batterseapower|Owner: igloo Type: feature request | Status: patch Priority: high |Milestone: 7.4.1 Component: Compiler | Version: 7.1 Keywords:| Testcase: Blockedby:| Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: None/Unknown -+-- Comment(by simonmar): I don't like the explicit layout idea. The goal so far has been to find a way to allow multi-clause multi-argument anonymous functions but without adding any inconsistencies to the language. Having `\` introduce a layout context fits the bill, but unfortunately it breaks many common idioms. Perhaps the only way to do this is to have a new keyword. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4359#comment:52 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #5288: Less noisy version of -fwarn-name-shadowing
#5288: Less noisy version of -fwarn-name-shadowing -+-- Reporter: batterseapower|Owner: Type: feature request | Status: new Priority: normal|Milestone: Component: Compiler | Version: 7.0.3 Keywords:| Testcase: Blockedby:| Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: None/Unknown -+-- Comment(by simonpj): I don't understand what you mean by saying a definition shadows itself. And while I sometimes make silly loops too (of the form `x = ...x...`), they may or may not involve shadowing. Maybe you can write a more precise spec, and argue why it's useful? Simon -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5288#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #5286: panic: getPredTyDescription EqPred [7.0 regression]
#5286: panic: getPredTyDescription EqPred [7.0 regression] -+-- Reporter: simonmar |Owner: simonpj Type: bug | Status: new Priority: highest |Milestone: 7.2.1 Component: Compiler | Version: 7.0.3 Keywords:| Testcase: Blockedby:| Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: Compile-time crash -+-- Changes (by simonpj): * owner: = simonpj -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5286#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #5287: The 'impossible' happened. solveDerivEqns: probable loop
#5287: The 'impossible' happened. solveDerivEqns: probable loop ---+ Reporter: agocorona |Owner: simonpj Type: bug | Status: new Priority: normal |Milestone: Component: Compiler| Version: 7.0.3 Keywords: solveDerivEqns | Testcase: Blockedby: | Difficulty: Os: Windows | Blocking: Architecture: x86 | Failure: Compile-time crash ---+ Changes (by simonpj): * owner: = simonpj -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5287#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #5288: Less noisy version of -fwarn-name-shadowing
#5288: Less noisy version of -fwarn-name-shadowing
-+--
Reporter: batterseapower|Owner:
Type: feature request | Status: new
Priority: normal|Milestone:
Component: Compiler | Version: 7.0.3
Keywords:| Testcase:
Blockedby:| Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
-+--
Comment(by batterseapower):
My thinking is that when I write:
{{{
foo rn = ... rn ...
where
rn = ... rn ...
}}}
My intention is almost invariably to bind a slightly-modified version of
rn. However, in the code above I have made a mistake and reused the old
name for the new version. What I should have written was:
{{{
foo rn = ... rn' ...
where
rn' = ... rn ...
}}}
The fact that the rn = ... rn ... binding shadowed an existing binding
called rn is the clue that I was trying to slightly-modify an existing
binding. I don't want to warn if rn = ... rn ... does not cause any
shadowing because no such clue exists.
Does that make more sense?
I used to write programs with this error at the rate of perhaps 1 program
per 20 hours of coding, but I'm getting better at avoiding it.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5288#comment:4
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Re: [GHC] #5283: Arrow command combinators: addTickHsExpr explodes in GHCi
#5283: Arrow command combinators: addTickHsExpr explodes in GHCi --+- Reporter: peteg| Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler |Version: 7.0.3 Resolution: duplicate| Keywords: Testcase: arrows/should_compile/T5283 | Blockedby: Difficulty: | Os: Unknown/Multiple Blocking: | Architecture: Unknown/Multiple Failure: Compile-time crash | --+- Changes (by simonpj): * testcase: = arrows/should_compile/T5283 -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5283#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #5275: Data.Typeable not backwards compatible
#5275: Data.Typeable not backwards compatible
-+--
Reporter: augustss |Owner:
Type: bug | Status: new
Priority: normal|Milestone:
Component: libraries/base| Version: 7.1
Keywords:| Testcase:
Blockedby:| Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
-+--
Comment(by simonpj):
Simon and I talked about this. We propose to change `Typeable.TyCon` from
this:
{{{
data TyCon = TyCon !Key String
}}}
to this:
{{{
data TyCon = TyCon !Key
String-- Package name
String-- Module name
String-- TyCon name
}}}
and add accessors for these fields. Then you can get the bits you want.
It's not enough to keep just the loacl name (like Integer) because there
might be many types with the same name.
A the same time we propose to get rid of the side-effected cache and use
MD5 checksums instead.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5275#comment:2
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Re: [GHC] #5288: Less noisy version of -fwarn-name-shadowing
#5288: Less noisy version of -fwarn-name-shadowing -+-- Reporter: batterseapower|Owner: Type: feature request | Status: new Priority: normal|Milestone: Component: Compiler | Version: 7.0.3 Keywords:| Testcase: Blockedby:| Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: None/Unknown -+-- Comment(by simonpj): I'm still hoping for a *specification*. Perhaps you mean report shadowing only for a recursive binding? -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/5288#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Quoting a quasi-quote
It was pointed out by Ben Millwood on the Cafe that there is an undocumented way to escape the closing oxford bracket of a quasi-quote using a backslash: [s|This quasi-quote contains this, \|], an escaped closing oxford bracket.|] The backslash itself cannot be escaped in this way: [s|Also contains an escaped bracket \\|] |] Thus there is a fairly strong limitation on the contents of a quasi-quote: it can never end in a backslash. This behavior is not mentioned in the GHC docs. Is it a mistake, or is it meant to be a supported feature? This behavior is a bit surprising to me. Since the whole point of a quasi-quoter is to allow the user to define syntax, you would think that the syntax for the quasi-quote itself would be as quiet as possible and stay out of the way. People who need to be able to escape the closing bracket can easily define their own syntax to do so. In any case, if this is indeed a feature, it certainly should be documented. Thanks, Yitz ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell] ANNOUNCE: string-qq-0.0.2
Ben Millwood wrote: I once spent some time and energy making [foo| bar baz |\] quux |] do the right thing for a quasiquoter I implemented, only to discover that GHC already supports [foo| bar baz \|] quux |]. So yes, you can escape it. Wow, that actually works. That is very surprising, counter-intuitive, and undocumented. Quasi-quotation is supposed to be a mechanism by which you can define your own compile-time syntax. One would expect GHC to stay out of the way as much as possible. People who need some way to quote |] can define their own syntax for that. And if that really is intended to be a supported feature, you would certainly think it important enough to warrant a mention in the GHC docs. So even if this works, I wouldn't rely on it until we get confirmation from the GHC team that it is indeed a supported a feature and won't go away in some future version of GHC. -Yitz ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell] ANNOUNCING: Hac PDX II - A Portland Haskell Hackathon
WHAT: A Haskell Hackathon WHEN: July 22-24 (Friday, Saturday, Sunday) 10:00 AM to 5:30 PM WHERE: Forth Avenue Building (FAB, 1900 SW 4th Ave) Room 10 Portland, Oregon 97201 WHERE, take 2: FAB10 is a small auditorium just inside the west most Harrison Street entrance. URL: http://haskell.org/haskellwiki/HacPDX-II WHAT, take 2: HacPDX-II is a Haskell Hackathon where beginners and experts alike can come to work on the Haskell projects of their choice - individually or in groups. If you don't have a project then never fear, come and pick one up or join a group (see the wiki for a list of projects). EQUIPMENT: You should bring a laptop with wireless (802.11). Ethernet is unavailable. Registration: Please RSVP by e-mailing thomas.dubuisson+hacpdx at gmail.com, as well as add your name to the attendees Wiki page (see above URL). Hope to see you there, Thomas ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[arch-haskell] AUR Comment for haskell-hdbc
from http://aur.archlinux.org/packages.php?ID=16103 federico_s wrote: Dependencies haskell-bytestring=0.9.1.7, haskell-containers=0.3.0.0, haskell-old-time=1.0.0.5, haskell-time=1.1.4 are obsolete. --- If you no longer wish to receive notifications about this package, please go the the above package page and click the UnNotify button. ___ arch-haskell mailing list arch-hask...@haskell.org http://www.haskell.org/mailman/listinfo/arch-haskell
[arch-haskell] AUR Comment for haskell-convertible
from http://aur.archlinux.org/packages.php?ID=23553 federico_s wrote: Dependencies haskell-containers=0.3.0.0, haskell-old-time=1.0.0.5, haskell-time=1.1.4 are obosolete. --- If you no longer wish to receive notifications about this package, please go the the above package page and click the UnNotify button. ___ arch-haskell mailing list arch-hask...@haskell.org http://www.haskell.org/mailman/listinfo/arch-haskell
[Haskell-cafe] what if two package contains same module?
it seems that cabal install different into different folders. if two package contains same module name, can they all exist? since cabal have no remvoe or uninstall. how can I hide some packages? Cheers! 吴兴博 Wu Xingbo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what if two package contains same module?
On 30 June 2011 17:40, 吴兴博 wux...@gmail.com wrote: it seems that cabal install different into different folders. if two package contains same module name, can they all exist? since cabal have no remvoe or uninstall. how can I hide some packages? ghc-pkg hide foo-1.2.3 This will work for using them in ghci and explicit ghc calls. Otherwise, when using packages built with cabal, you specify which libraries you use and Cabal hides the rest. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what if two package contains same module?
吴兴博 wrote: it seems that cabal install different into different folders. if two package contains same module name, can they all exist? since cabal have no remvoe or uninstall. how can I hide some packages? The ghc-pkg program organizes GHC's package database. You want to run the command ghc-pkg hide offending-package Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] overloading show function
Am 29.06.2011 um 23:50 schrieb Philipp Schneider: Hi cafe, in my program i use a monad of the following type newtype M a = M (State - (a, State)) i use the monad in two different ways. The type variable a can be a pair as in interp :: Term - Environment - M (Value,Environment) and it can be just a value as in type Environment = [(Name, Either Value (M Value))] Simple rule: Never return an environment! An environment contains local variable bindings, so no subcomputation will ever need to return its environment. I don't know anything about the language your program interprets, but I'm sure that you can rewrite function interp as interp :: Term - Environment - M Value The structure of the interpreter will become clearer and your problem will vanish. now in any case when i print the monad, i just want to print the value and never the environment. More specific i want to use somthing like the following instance (Show a,Show b) = Show (M (a,b)) where show (M f) = let ((v,_), s) = f 0 in Value: ++ show v ++ Count: ++ show s instance Show a = Show (M a) where show (M f) = let (v, s) = f 0 in Value: ++ show v ++ Count: ++ show s however this gives me the following error message: Overlapping instances for Show (M (Value, Environment)) arising from a use of `print' Matching instances: instance (Show a, Show b) = Show (M (a, b)) -- Defined at /home/phil/code/haskell/vorlesung/ue09/ue09-3c3.hs:78:10-42 instance Show a = Show (M a) -- Defined at /home/phil/code/haskell/vorlesung/ue09/ue09-3c3.hs:82:10-29 In a stmt of an interactive GHCi command: print it Any ideas how to fix it? Thanks! Philipp ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] overloading show function
An environment contains local variable bindings, so no subcomputation will ever need to return its environment. - That is not true. A subcomputation can possible modify an environment except the language forbids such a case. On 06/30/2011 02:36 PM, Holger Siegel wrote: Am 29.06.2011 um 23:50 schrieb Philipp Schneider: Hi cafe, in my program i use a monad of the following type newtype M a = M (State - (a, State)) i use the monad in two different ways. The type variable a can be a pair as in interp :: Term - Environment - M (Value,Environment) and it can be just a value as in type Environment = [(Name, Either Value (M Value))] Simple rule: Never return an environment! An environment contains local variable bindings, so no subcomputation will ever need to return its environment. I don't know anything about the language your program interprets, but I'm sure that you can rewrite function interp as interp :: Term - Environment - M Value The structure of the interpreter will become clearer and your problem will vanish. now in any case when i print the monad, i just want to print the value and never the environment. More specific i want to use somthing like the following instance (Show a,Show b) = Show (M (a,b)) where show (M f) = let ((v,_), s) = f 0 in Value: ++ show v ++ Count: ++ show s instance Show a = Show (M a) where show (M f) = let (v, s) = f 0 in Value: ++ show v ++ Count: ++ show s however this gives me the following error message: Overlapping instances for Show (M (Value, Environment)) arising from a use of `print' Matching instances: instance (Show a, Show b) = Show (M (a, b)) -- Defined at /home/phil/code/haskell/vorlesung/ue09/ue09-3c3.hs:78:10-42 instance Show a = Show (M a) -- Defined at /home/phil/code/haskell/vorlesung/ue09/ue09-3c3.hs:82:10-29 In a stmt of an interactive GHCi command: print it Any ideas how to fix it? Thanks! Philipp ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Confused about my IterIO code
Hi Hakell Cafe, I'm struggling to understand my unambitious IterIO code that somehow manages to work. Basically I run an echo server that is supposed to read from a socket line by line and write back to the socket with all the characters in the line reversed: import Control.Exception import Control.Monad import Control.Monad.Trans import Data.IterIO import Data.IterIO.Inum import Network import System.IO import System.IO.Error (isEOFError) import qualified Data.ByteString.Lazy as L import qualified Data.ByteString.Lazy.Char8 as C iterHandle' :: (MonadIO m) = Handle - IO (Iter L.ByteString m (), Onum L.ByteString m a) iterHandle' = iterHandle main = withSocketsDo $ do sListen - listenOn (PortNumber 8000) putStrLn Listening on Port 8000 forkIO $ forever $ do (sSession, hostname, port) - accept sListen hSetBuffering sSession NoBuffering putStrLn (Connected to ++ hostname ++ : ++ show port) forkIO $ do (iter, enum) - iterHandle' sSession enum |$ inumReverseLines .| iter putStrLn Press CTRL-D to quit. exitOnCtrlD inumReverseLines :: (Monad m) = Inum L.ByteString L.ByteString m a inumReverseLines = mkInum $ do line - lineI return (L.reverse (L.concat [line, C.pack \n])) exitOnCtrlD = try getLine = either (\e - unless (isEOFError e) $ ioError e) (const exitOnCtrlD) When I run it, it does this: asdfghc7@hoggy-nn:/home/hoggy$ nc localhost 8000 1234 4321 4321 1234 abcde edcba The red lines are the replies from my echo server. But all I've done is: enum |$ inumReverseLines .| iter inumReverseLines = mkInum $ do line - lineI return (L.reverse (L.concat [line, C.pack \n])) No attempt was made to reverse more than one line - at least as far as I can see. What have I done wrong that it should work so well? Also, is there a better way to do this? Cheers, -John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Confused about my IterIO code
On Thu, Jun 30, 2011 at 09:53, John Ky newho...@gmail.com wrote: enum |$ inumReverseLines .| iter inumReverseLines = mkInum $ do line - lineI return (L.reverse (L.concat [line, C.pack \n])) No attempt was made to reverse more than one line - at least as far as I can see. What have I done wrong that it should work so well? An iterator that doesn't iterate isn't very useful. -- 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
Re: [Haskell-cafe] Confused about my IterIO code
At Thu, 30 Jun 2011 23:53:02 +1000, John Ky wrote: But all I've done is: enum |$ inumReverseLines .| iter inumReverseLines = mkInum $ do line - lineI return (L.reverse (L.concat [line, C.pack \n])) mkInum repeatedly invokes its iter argument so as to keep producing chunks. If you want to reverse only one line, it might be easiest to use something along the lines of: mkInumM $ do line - lineI ifeed (L.reverse (L.concat [line, C.pack \n])) mkInumM is a more manual Inum construction function that doesn't automatically do things like loop or handle EOF conditions. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] overloading show function
On 06/30/2011 02:36 PM, Holger Siegel wrote: Am 29.06.2011 um 23:50 schrieb Philipp Schneider: Hi cafe, in my program i use a monad of the following type newtype M a = M (State - (a, State)) i use the monad in two different ways. The type variable a can be a pair as in interp :: Term - Environment - M (Value,Environment) and it can be just a value as in type Environment = [(Name, Either Value (M Value))] Simple rule: Never return an environment! An environment contains local variable bindings, so no subcomputation will ever need to return its environment. I don't know anything about the language your program interprets, but I'm sure that you can rewrite function interp as interp :: Term - Environment - M Value The structure of the interpreter will become clearer and your problem will vanish. Hello Holger, I'm giving two lambda interpreters. The first one is a call by value interpreter, the second one a call by name interpreter which are described in Philip Wadler's paper The essence of functional programming page 4 and 12. Now my task is to write a lazy lambda interpreter. The exercise is more playful than serious since Wadler's call by value interpreter is, since written in lazy Haskell, already a lazy lambda interpreter. (To get true call by value one would need to force evaluations of the arguments with the seq function.) For both of Wadler's interpreters the type of the interpertation function is: interp :: Term - Environment - M Value Now to simulate lazy interpretation i need to do the following: Decide is the value I need already evaluated or is it still a computation. In the later case I need to evaluate it and save its value in the environment. This is the reason I changed the type of the interpretation function to: interp :: Term - Environment - M (Value,Environment) I appened my full interpreter. If you can find a more elegant way to save the newly interpreted values, you are more than welcome to show my how to do it. Cheers, Philipp ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what if two package contains same module?
吴兴博 wux...@gmail.com wrote: it seems that cabal install different into different folders. if two package contains same module name, can they all exist? since cabal have no remvoe or uninstall. how can I hide some packages? Alternatively for small programs for which you don't use a Cabal file you can use the PackageImports extension (-XPackageImports) and import modules from specific packages. For example both the 'pool' and the 'resource-pool' packages provide a Data.Pool module. You can choose to import the one from 'resource-pool' using this: import resource-pool Data.Pool Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife = sex) http://ertes.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] overloading show function
On 06/30/2011 08:25 PM, Philipp Schneider wrote:
On 06/30/2011 02:36 PM, Holger Siegel wrote:
Am 29.06.2011 um 23:50 schrieb Philipp Schneider:
Hi cafe,
in my program i use a monad of the following type
newtype M a = M (State - (a, State))
i use the monad in two different ways. The type variable a can be a
pair as in
interp :: Term - Environment - M (Value,Environment)
and it can be just a value as in
type Environment = [(Name, Either Value (M Value))]
Simple rule: Never return an environment!
An environment contains local variable bindings, so no subcomputation will
ever need to return its environment. I don't know anything about the
language your program interprets, but I'm sure that you can rewrite function
interp as
interp :: Term - Environment - M Value
The structure of the interpreter will become clearer and your problem will
vanish.
Hello Holger,
I'm giving two lambda interpreters. The first one is a call by value
interpreter, the second one a call by name interpreter which are
described in Philip Wadler's paper The essence of functional
programming page 4 and 12. Now my task is to write a lazy lambda
interpreter. The exercise is more playful than serious since Wadler's
call by value interpreter is, since written in lazy Haskell, already a
lazy lambda interpreter. (To get true call by value one would need to
force evaluations of the arguments with the seq function.)
For both of Wadler's interpreters the type of the interpertation
function is:
interp :: Term - Environment - M Value
Now to simulate lazy interpretation i need to do the following: Decide
is the value I need already evaluated or is it still a computation. In
the later case I need to evaluate it and save its value in the
environment. This is the reason I changed the type of the interpretation
function to:
interp :: Term - Environment - M (Value,Environment)
I appened my full interpreter. If you can find a more elegant way to
save the newly interpreted values, you are more than welcome to show my
how to do it.
Cheers,
Philipp
I forgot to add the interpreter.
{-# LANGUAGE OverlappingInstances #-}
import Prelude hiding (lookup, fail)
import Control.Monad
-- Basiswerte
data Value= WrongAd
| WrongAp
| WrongL
| Num Int
| Fun (Either Value (M Value) - M Value)
instance Show Value where
show WrongAd= wrong add
show WrongAp= wrong app
show WrongL= wrong lookup
show (Num i) = show i
show (Fun f) = function
-- Terme
data Term = Var Name
| Con Int
| Add Term Term
| Lam Name Term
| App Term Term deriving Show
-- Interpretation der Terme (Lazy evaluation)
interp :: Term - Environment - M (Value,Environment)
interp (Var x) e = lookup x e
interp (Con i) e = return (Num i,e)
interp (Add u v) e = do
(a,e) - interp u e
(b,e) - interp v e
s - add a b
return (s,e)
interp (Lam x v) e = return (Fun (\m - (interp v ((x, m):e)) = return . fst) , e)
interp (App t u) e = do
(f,e) - interp t e
a - (apply f (Right ((interp u e) = return . fst)))
return (a,e)
add :: Value - Value - M Value
add (Num i) (Num j) = tick = (\() - return (Num (i+j)))
add a b = return WrongAd
apply :: Value - Either Value (M Value) - M Value
apply (Fun k) a= tick = (\() - k a)
apply notFun a = return WrongAp
-- Umgebung
type Environment = [(Name, Either Value (M Value))]
type Name = String
lookup :: Name - Environment - M (Value,Environment)
lookup x eComplete = lookup_h x eComplete
where
lookup_h x []= return (WrongL,[])
lookup_h x e@((y,b):etl) =
if x==y then case b of
-- schon ausgewertet
Left a - return (a,e)
-- noch nicht ausgewertet (speichere den ausgewerteten Wert)
Right a - (a = (\x- return (x, (y,Left x):eComplete)))
else lookup_h x etl
-- Lazy-Interpreter zaehlt die Reduktionen (Wadler: Beispiel 9)
type State = Int
newtype M a = M (State - (a, State))
tick = M (\s - ((), s+1))
instance (Show a,Show b) = Show (M (a,b)) where
show (M f) = let ((v,_), s) = f 0 in
Value: ++ show v ++ Count: ++ show s
instance Show a = Show (M a) where
show (M f) = let (v, s) = f 0 in
Value: ++ show v ++ Count: ++ show s
instance Monad M where
return a = M (\s - (a, s))
(M m) = k = M (\s0 - let (a, s1) = m s0
(M m') = k a
in m' s1
)
fail s = error s -- wird nicht aufgerufen
-- Beispiele:
-- test :: Term - String
test t = (interp t [])
term0 = (Con 10)
term0' = (Var x)
term1 = (Add (Con 10) (Con 11))
term2 = (Lam x (Add (Var x) (Con 10)))
term3 = (App term2 (Con 11))
term4 = (Lam x (Add (Var x) (Var x)))
term5 = (App term4 term1)
term6 = (Lam x (Lam y (Add (Var x) (Var y
term7 = (App term6 (Con 10))
term8 =
[Haskell-cafe] ANNOUNCE: mime-mail-ses 0.0.0
Hi all, I'd like to announce the first release of mime-mail-ses[1]. This provides easy integration between the mime-mail package[2] and Amazon's Simple Email Service. This package was written for the Haskellers website[3], purely because I despise setting up mail servers. There aren't many more features planned, though hopefully in the future it will integrate more closely with Aristid's aws package[4]. Also, a big thank you to Thomas DuBuisson for crypto-api[5] and Vincent Hanquez for cryptohash[6]. Those two packages make it very easy to write applications that require cryptographic authentication. Michael [1] http://hackage.haskell.org/package/mime-mail-ses [2] http://hackage.haskell.org/package/mime-mail [3] http://www.haskellers.com/ [4] http://hackage.haskell.org/package/aws [5] http://hackage.haskell.org/package/crypto-api [6] http://hackage.haskell.org/package/cryptohash ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] overloading show function
Am 30.06.2011 um 20:23 schrieb Philipp Schneider: On 06/30/2011 02:36 PM, Holger Siegel wrote: Am 29.06.2011 um 23:50 schrieb Philipp Schneider: Hi cafe, in my program i use a monad of the following type newtype M a = M (State - (a, State)) i use the monad in two different ways. The type variable a can be a pair as in interp :: Term - Environment - M (Value,Environment) and it can be just a value as in type Environment = [(Name, Either Value (M Value))] Simple rule: Never return an environment! An environment contains local variable bindings, so no subcomputation will ever need to return its environment. I don't know anything about the language your program interprets, but I'm sure that you can rewrite function interp as interp :: Term - Environment - M Value The structure of the interpreter will become clearer and your problem will vanish. Hello Holger, I'm giving two lambda interpreters. The first one is a call by value interpreter, the second one a call by name interpreter which are described in Philip Wadler's paper The essence of functional programming page 4 and 12. Now my task is to write a lazy lambda interpreter. The exercise is more playful than serious since Wadler's call by value interpreter is, since written in lazy Haskell, already a lazy lambda interpreter. (To get true call by value one would need to force evaluations of the arguments with the seq function.) Hello Philipp, that's a nice exercise. For both of Wadler's interpreters the type of the interpertation function is: interp :: Term - Environment - M Value Now to simulate lazy interpretation i need to do the following: Decide is the value I need already evaluated or is it still a computation. In the later case I need to evaluate it and save its value in the environment. This is the reason I changed the type of the interpretation function to: interp :: Term - Environment - M (Value,Environment) But that won't work: After you have evaluated an entry of the environment, you store the resulting value but you throw away its updated environment. That means, you lose the results of all subcomputations instead of propagating them to all other copies of the environment. Consider the following expression: let x = big_computation in let y = x in y + x First, big_computation is bound to the name x, resulting in an environment [(x, big_computation)]. Then a closure consisting of this environment together with the right hand side 'x' is bound to the name y. Now y+x is evaluated: The closure is entered, and from its environment the content of x - a call to big_computation - is looked up. Now big_computation is evaluated and the result is bound to x in this environment. After that, this result is also returned as the value of y. But when returning from the evaluation of y, the environment with the updated value of x is lost and you have to re-evaluate it in order to calculate x+y! And that is why I say never return an environment. It is either wrong or unnecessary or the resulting semantics of the interpreter is hard to comprehend. In order to implement lazy evaluation correctly, you have to maintain some global state in which the thunks are updated. For example, your environment could bind IORefs that contain unevaluated thunks to variable names and update them when the thunk is evaluated. But then your interpreter has to run in the IO monad. By the way, do you already know Peter Sestoft's paper Deriving a lazy abstract machine? Cheers, Holger ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCING: Hac PDX II - A Portland Haskell Hackathon
WHAT: A Haskell Hackathon WHEN: July 22-24 (Friday, Saturday, Sunday) 10:00 AM to 5:30 PM WHERE: Forth Avenue Building (FAB, 1900 SW 4th Ave) Room 10 Portland, Oregon 97201 WHERE, take 2: FAB10 is a small auditorium just inside the west most Harrison Street entrance. URL: http://haskell.org/haskellwiki/HacPDX-II WHAT, take 2: HacPDX-II is a Haskell Hackathon where beginners and experts alike can come to work on the Haskell projects of their choice - individually or in groups. If you don't have a project then never fear, come and pick one up or join a group (see the wiki for a list of projects). EQUIPMENT: You should bring a laptop with wireless (802.11). Ethernet is unavailable. Registration: Please RSVP by e-mailing thomas.dubuisson+hacpdx at gmail.com, as well as add your name to the attendees Wiki page (see above URL). Hope to see you there, Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCING: Hac PDX II - A Portland Haskell Hackathon
On Thu, Jun 30, 2011 at 12:55 PM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: WHAT: A Haskell Hackathon WHEN: July 22-24 (Friday, Saturday, Sunday) 10:00 AM to 5:30 PM WHERE: Forth Avenue Building (FAB, 1900 SW 4th Ave) Room 10 Portland, Oregon 97201 ... Registration: Please RSVP by e-mailing thomas.dubuisson+hacpdx at gmail.com, as well as add your name to the attendees Wiki page (see above URL). Is anybody from the Eugene area considering going? We could organize a carpool. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] overloading show function
On 06/30/2011 09:49 PM, Holger Siegel wrote: Am 30.06.2011 um 20:23 schrieb Philipp Schneider: On 06/30/2011 02:36 PM, Holger Siegel wrote: Am 29.06.2011 um 23:50 schrieb Philipp Schneider: Hi cafe, in my program i use a monad of the following type newtype M a = M (State - (a, State)) i use the monad in two different ways. The type variable a can be a pair as in interp :: Term - Environment - M (Value,Environment) and it can be just a value as in type Environment = [(Name, Either Value (M Value))] Simple rule: Never return an environment! An environment contains local variable bindings, so no subcomputation will ever need to return its environment. I don't know anything about the language your program interprets, but I'm sure that you can rewrite function interp as interp :: Term - Environment - M Value The structure of the interpreter will become clearer and your problem will vanish. Hello Holger, I'm giving two lambda interpreters. The first one is a call by value interpreter, the second one a call by name interpreter which are described in Philip Wadler's paper The essence of functional programming page 4 and 12. Now my task is to write a lazy lambda interpreter. The exercise is more playful than serious since Wadler's call by value interpreter is, since written in lazy Haskell, already a lazy lambda interpreter. (To get true call by value one would need to force evaluations of the arguments with the seq function.) Hello Philipp, that's a nice exercise. For both of Wadler's interpreters the type of the interpertation function is: interp :: Term - Environment - M Value Now to simulate lazy interpretation i need to do the following: Decide is the value I need already evaluated or is it still a computation. In the later case I need to evaluate it and save its value in the environment. This is the reason I changed the type of the interpretation function to: interp :: Term - Environment - M (Value,Environment) But that won't work: After you have evaluated an entry of the environment, you store the resulting value but you throw away its updated environment. That means, you lose the results of all subcomputations instead of propagating them to all other copies of the environment. Consider the following expression: let x = big_computation in let y = x in y + x First, big_computation is bound to the name x, resulting in an environment [(x, big_computation)]. Then a closure consisting of this environment together with the right hand side 'x' is bound to the name y. Now y+x is evaluated: The closure is entered, and from its environment the content of x - a call to big_computation - is looked up. Now big_computation is evaluated and the result is bound to x in this environment. After that, this result is also returned as the value of y. But when returning from the evaluation of y, the environment with the updated value of x is lost and you have to re-evaluate it in order to calculate x+y! Hello Holger, Can you give me an example of a lambda term in which this would be an issue? Evaluating the following works just fine in my implementation. interp (App (Lam x (Add (Var x) (Var x))) big_computation) [] When the first variable x is evaluated my interp function returns the value and the updated environment. Then to evaluate the second variable the value is just looked up from this environment. Of course in the following big_computation would be evaluated twice (App (Lam x (App (Lam y (Add (Var x) (Var y))) big_computation)) big_computation) But i simply don't have a concept like let x=y. And that is why I say never return an environment. It is either wrong or unnecessary or the resulting semantics of the interpreter is hard to comprehend. In order to implement lazy evaluation correctly, you have to maintain some global state in which the thunks are updated. For example, your environment could bind IORefs that contain unevaluated thunks to variable names and update them when the thunk is evaluated. But then your interpreter has to run in the IO monad. I agree that this would be the proper way to do it, but I was trying to minimize the use of monads since they have just been introduced in the course. By the way, do you already know Peter Sestoft's paper Deriving a lazy abstract machine? I haven't read is so far, but thanks for pointing it out. Cheers, Holger Cheers, Philipp ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] overloading show function
Am 30.06.2011 um 22:57 schrieb Philipp Schneider: On 06/30/2011 09:49 PM, Holger Siegel wrote: (...) But that won't work: After you have evaluated an entry of the environment, you store the resulting value but you throw away its updated environment. That means, you lose the results of all subcomputations instead of propagating them to all other copies of the environment. Consider the following expression: let x = big_computation in let y = x in y + x First, big_computation is bound to the name x, resulting in an environment [(x, big_computation)]. Then a closure consisting of this environment together with the right hand side 'x' is bound to the name y. Now y+x is evaluated: The closure is entered, and from its environment the content of x - a call to big_computation - is looked up. Now big_computation is evaluated and the result is bound to x in this environment. After that, this result is also returned as the value of y. But when returning from the evaluation of y, the environment with the updated value of x is lost and you have to re-evaluate it in order to calculate x+y! Hello Holger, Can you give me an example of a lambda term in which this would be an issue? Evaluating the following works just fine in my implementation. interp (App (Lam x (Add (Var x) (Var x))) big_computation) [] When the first variable x is evaluated my interp function returns the value and the updated environment. Then to evaluate the second variable the value is just looked up from this environment. Of course in the following big_computation would be evaluated twice (App (Lam x (App (Lam y (Add (Var x) (Var y))) big_computation)) big_computation) But i simply don't have a concept like let x=y. App (Lam x (App (Lam y (Add (Var y) (Var x))) (Var x ))) (Con 2) takes three reduction steps, which is correct, but App (Lam x (App (Lam y (Add (Var y) (Var x))) (Var x ))) (Add (Con 1)(Con 1)) takes five reduction steps although it should take only four. And that is why I say never return an environment. It is either wrong or unnecessary or the resulting semantics of the interpreter is hard to comprehend. In order to implement lazy evaluation correctly, you have to maintain some global state in which the thunks are updated. For example, your environment could bind IORefs that contain unevaluated thunks to variable names and update them when the thunk is evaluated. But then your interpreter has to run in the IO monad. I agree that this would be the proper way to do it, but I was trying to minimize the use of monads since they have just been introduced in the course. That shouldn't be too hard. Just change your definition of monad M to newtype M a = M (State - IO (a, State)) and define the corresponding monad instance as an exercise :) (or ask me by private mail if you like). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Printing the empty list.
GHCi seems to be clever about some things: If I try to print the empty list in ghci, I encounter no problems: Prelude [] [] Prelude show [] [] Prelude print [] [] Even though the type of the list is clearly unknown, it must be picking SOME type. (why does it print [] instead of )? If I write a program in a file and load it in main = print [] Then I get the ambiguous type variable error that I would expect. Why doesn't ghci generate this error at the prompt? -- Borrow my books: http://goo.gl/UBbSH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Printing the empty list.
On Thu, Jun 30, 2011 at 18:58, Joshua Ball joshbb...@gmail.com wrote: GHCi seems to be clever about some things: GHCi uses extended defaulting rules unless told otherwise, so in the absence of anything else it uses () as the type. You can enable this in GHC as well, with -XExtendedDefaultRules. See http://www.haskell.org/ghc/docs/latest/html/users_guide/interactive-evaluation.html#extended-default-rules -- 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
Re: [Haskell-cafe] Printing the empty list.
On 1 July 2011 08:58, Joshua Ball joshbb...@gmail.com wrote: GHCi seems to be clever about some things: If I try to print the empty list in ghci, I encounter no problems: Prelude [] [] Prelude show [] [] Prelude print [] [] Even though the type of the list is clearly unknown, it must be picking SOME type. (why does it print [] instead of )? Type defaulting: if you don't specify a type, then ghci makes it [Integer]. If I write a program in a file and load it in main = print [] Then I get the ambiguous type variable error that I would expect. Why doesn't ghci generate this error at the prompt? Because ghc doesn't do type defaulting. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] overloading show function
On 06/30/2011 11:46 PM, Holger Siegel wrote: Am 30.06.2011 um 22:57 schrieb Philipp Schneider: On 06/30/2011 09:49 PM, Holger Siegel wrote: (...) But that won't work: After you have evaluated an entry of the environment, you store the resulting value but you throw away its updated environment. That means, you lose the results of all subcomputations instead of propagating them to all other copies of the environment. Consider the following expression: let x = big_computation in let y = x in y + x First, big_computation is bound to the name x, resulting in an environment [(x, big_computation)]. Then a closure consisting of this environment together with the right hand side 'x' is bound to the name y. Now y+x is evaluated: The closure is entered, and from its environment the content of x - a call to big_computation - is looked up. Now big_computation is evaluated and the result is bound to x in this environment. After that, this result is also returned as the value of y. But when returning from the evaluation of y, the environment with the updated value of x is lost and you have to re-evaluate it in order to calculate x+y! Hello Holger, Can you give me an example of a lambda term in which this would be an issue? Evaluating the following works just fine in my implementation. interp (App (Lam x (Add (Var x) (Var x))) big_computation) [] When the first variable x is evaluated my interp function returns the value and the updated environment. Then to evaluate the second variable the value is just looked up from this environment. Of course in the following big_computation would be evaluated twice (App (Lam x (App (Lam y (Add (Var x) (Var y))) big_computation)) big_computation) But i simply don't have a concept like let x=y. App (Lam x (App (Lam y (Add (Var y) (Var x))) (Var x ))) (Con 2) takes three reduction steps, which is correct, but App (Lam x (App (Lam y (Add (Var y) (Var x))) (Var x ))) (Add (Con 1)(Con 1)) takes five reduction steps although it should take only four. Ok, I now see the problem. Thanks for pointing it out to me. And that is why I say never return an environment. It is either wrong or unnecessary or the resulting semantics of the interpreter is hard to comprehend. In order to implement lazy evaluation correctly, you have to maintain some global state in which the thunks are updated. For example, your environment could bind IORefs that contain unevaluated thunks to variable names and update them when the thunk is evaluated. But then your interpreter has to run in the IO monad. I agree that this would be the proper way to do it, but I was trying to minimize the use of monads since they have just been introduced in the course. That shouldn't be too hard. Just change your definition of monad M to newtype M a = M (State - IO (a, State)) and define the corresponding monad instance as an exercise :) (or ask me by private mail if you like). I'll try to implement it tomorrow. Hopefully I'll succeed without your help. ;) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Printing the empty list.
On Fri, Jul 01, 2011 at 09:05:05AM +1000, Ivan Lazar Miljenovic wrote: On 1 July 2011 08:58, Joshua Ball joshbb...@gmail.com wrote: GHCi seems to be clever about some things: If I try to print the empty list in ghci, I encounter no problems: Prelude [] [] Prelude show [] [] Prelude print [] [] Even though the type of the list is clearly unknown, it must be picking SOME type. (why does it print [] instead of )? Type defaulting: if you don't specify a type, then ghci makes it [Integer]. In this case I'm pretty sure it is [()] since there is only a Show constraint. If there were a Num constraint it would pick Integer. Prelude sum [] 0 Prelude :t it it :: Integer -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Printing the empty list.
On 1 July 2011 11:35, Brent Yorgey byor...@seas.upenn.edu wrote: On Fri, Jul 01, 2011 at 09:05:05AM +1000, Ivan Lazar Miljenovic wrote: On 1 July 2011 08:58, Joshua Ball joshbb...@gmail.com wrote: GHCi seems to be clever about some things: If I try to print the empty list in ghci, I encounter no problems: Prelude [] [] Prelude show [] [] Prelude print [] [] Even though the type of the list is clearly unknown, it must be picking SOME type. (why does it print [] instead of )? Type defaulting: if you don't specify a type, then ghci makes it [Integer]. In this case I'm pretty sure it is [()] since there is only a Show constraint. If there were a Num constraint it would pick Integer. Yeah, I forgot about () -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Patterns for processing large but finite streams
Hi, I'm rewriting timeplot to avoid holding the whole input in memory, and naturally a problem arises: How to represent large but finite streams and functions that process them, returning other streams or some kinds of aggregate values? Examples: * Adjacent differences of a stream of numbers * Given a stream of numbers with times, split it into buckets by time of given width and produce a stream of (bucket, 50%,75% and 90% quantiles in this bucket) * Sum a stream of numbers Is this, perhaps, what comonads are for? Or iteratees? -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to implement the mean function
Hi guys, I just started learning some Haskell. I want to implement a mean function to compute the mean of a list. The signature of the function is: mean :: (Num a, Fractional b) = [a] - b But when I implement this simple function, the compiler keep whining at me on type errors. I know this is wrong: mean xs = sum xs / length xs But how to get it right? Thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[arch-haskell] AUR Out-of-date Notification for haskell-ghc-syb-utils
Your package haskell-ghc-syb-utils has been flagged out of date by federico_s [1]. You may view your package at: http://aur.archlinux.org/packages.php?ID=37650 [1] - http://aur.archlinux.org/account.php?Action=AccountInfoID=29078 ___ arch-haskell mailing list arch-haskell@haskell.org http://www.haskell.org/mailman/listinfo/arch-haskell
