- Glasgow-haskell-users

Type-level operators
by Stefan Holdermans 20 Apr '11

20 Apr '11

Simon, Regarding the note you attached to the Trac ticket on the pretty-printing of kind ascriptions (http://hackage.haskell.org/trac/ghc/ticket/5141#comment:2) > Note, though, that it's likely that we're considering making operators > like '*' into type ''constructors'' rather that type ''variables'. This > is inconsitent with terms, but is jolly convenient: > {{{ > data a + b = Left a | Right b > }}} > Of course there'll be a flag. But let us know if you think that having > operators be type variables is very useful. (I tend to think it's more > confusing than useful.) I myself am perfectly alright with being "forced" to write {{{ data a :+: b = Left a | Right b }}} Although I don't have a *convincing* example of the usefulness of operators as type variables, I like the idea of consistency with the term level: IMO it keeps things predictable. And even as it may not qualify as convincing, I do remember having written code similar to {{{ data (f :+: g) a = Inl (f a) | Inr (g a) data (f :*: g) a = f a :*: g a class FunctorOp ((&) :: (* -> *) -> (* -> *) -> (* -> *)) where ... instance FunctorOp (:+:) where ... instance FunctorOp (:*:) where ... class FunctorOp (&) => CommOp (&) where comm :: f & g -> g & f instance CommOp (:+:) where ... instance CommOp (:*:) where ... f :: (CommOp (&), Functor f, Functor g) -> f & g -> ... f ... = ... }}} All this, of course, just to put in my tuppence worth. Cheers, Stefan

1 0

Installation
by Luca Ciciriello 20 Apr '11

20 Apr '11

Hi All.I'm using GHC with MacOS X 10.6.7 (Xcode4). I've installed GHC 7.0.3 and the HackageDB package hsgsom. Then, for my motivation, I've uninstalled GHC.To remove GHC I've used the uninstaller tool and I've manually removed the folder /Library/Frameworks/GHC.framework. I've also manually removed the folder /Users/MyUser/Library/Haskell and the folder /Users/MyUser/.cabal Now I've installed GHC again, but when I try to install the package hsgsom cabal tells to me that the package is already installed and I have to use the --reinstall flag. So, where the information of the installed packages are stored on my system? How can I remove all Haskell dependencies from my system in order to start with a clean installation? Thanks in advance for any answer. Luca.

2 2

Using the GHC heap profiler
by Tim Docker 19 Apr '11

19 Apr '11

My question on the ghc heap profiler on stack overflow: http://stackoverflow.com/questions/5306717/how-should-i-interpret-the-outpu… remains unanswered :-( Perhaps that's not the best forum. Is there someone here prepared to explain how the memory usage in the heap profiler relates to the "Live Bytes" count shown in the garbage collection statistics? Many thanks, Tim

6 12

C-- roundtripping: switch, if and other control flow statements
by Edward Z. Yang 15 Apr '11

15 Apr '11

Hello all, I'm interested in improving GHC's C-- parser's support (and also making accomodations for the parser in our C-- pretty-printer) to the point where we can round-trip output from -ddump-opt-cmm with no semantic change. There are several roadblocks on the way here, but the one I'm currently tackling is the fact that the parser does not understand flow control statements like such: if (b) goto foo; It requires that the statement be closed in braces, and this will generate a new, anonymous block containing the instruction: if (b) { goto foo; } becomes if (b) goto temp ... temp: goto foo; This is, somewhat surprisingly, preventing me from getting a nice minimal test-case for a bug in the linear register allocator. I need a way to not get an anonymous block being generated. I've tried extending the grammar to accept both, but for switch statements making the change at the obvious point introduces a reduce-reduce conflict. I suspect I can hack my way around it, but for now I've renamed the keyword to 'raw_switch', which doesn't accept blocks on the right side of the case. Cheers, Edward

1 0

C-- source highlighting using source-highlight
by Johan Tibell 15 Apr '11

15 Apr '11

Hi, I've thrown together a small source-highlight language file for C--. You can use it to e.g. highlight C-- code when piped through less. ### Installion ### # This works on Debian/Ubuntu $ sudo apt-get install source-highlight # Put this file anywhere $ cat $HOME/cmm.lang comment start "//" # multi-line comments comment delim "/*" "*/" multiline string delim "\"" "\"" escape "\\" keyword = "aborts|align|aligned|also|as|big|bits|byteorder|case|const", "continuation|cut|cuts|else|equal|export|foreign|goto|if|import|in", "invariant|invisible|jump|little|memsize|pragma|reads|register", "return|returns|section|semi|span|stackdata|switch|target|targets|to", "typedef|unicode|unwinds|writes" number = '\<[+-]?((0x[[:xdigit:]]+)|(([[:digit:]]*\.)? [[:digit:]]+([eE][+-]?[[:digit:]]+)?))u?((int(?:8|16|32|64))|L)?\>' ### Usage ### $ ghc <source> -ddump-cmm | source-highlight --lang-def=$HOME/cmm.lang -f esc -s cmm | less -R Johan

2 1

Meaning of ghc-pkg package-conf flags
by C Rodrigues 15 Apr '11

15 Apr '11

Hello, I'd like to know how ghc-pkg searches package databases and how the command-line flags affect the search. My model of ghc-pkg was that it builds a list of package databases and then searches them starting from the head. I'd like to work with a sandboxed local package database. Looking at what ghc-pkg list prints, I can infer what database list it's using: ghc-pkg list: [user-db, global-db] ghc-pkg list --global: [global-db] ghc-pkg list --global --package-conf=$HOME/sandbox/package.conf.d: [sandbox-db, global-db] However, even though ghc-pkg doesn't show my user database, it still reports broken packages that are in my user database. So ghc-pkg isn't really scanning packages according to this database list. What is it doing?

2 1

Rebuilding ghc changes interface hashes?
by Joachim Breitner 10 Apr '11

10 Apr '11

Dear ghc developers, I am currently rebuilding ghc-7.0.2 to upload some packaging changes. Unfortunately, this had the effect of changing the package id of "base", which would require rebuilding every Haskell library. In the times of ghc-6.12, rebuilding the compiler left the hashes intact. Is there anything new in ghc-7 that interferes here? Also, the initial upload was built using ghc-6.12.1, while the upload now is build with ghc-7.0.2. Given that it is a two-stage compiler, I assume that the output should be identical, but it seems not to be the case. Any idea what could be causing this? Greetings, Joachim -- Joachim "nomeata" Breitner Debian Developer nomeata(a)debian.org | ICQ# 74513189 | GPG-Keyid: 4743206C JID: nomeata(a)joachim-breitner.de | http://people.debian.org/~nomeata

4 14

Changing language options in ghci at runtime
by Simon Hengel 09 Apr '11

09 Apr '11

Hello, does anyone know whether you can somehow change the currently active language flags during a ghci session (say change what `:show languages' outputs)? If no, is this possible by using the GHC API? Cheers, Simon

2 2

Strange performance effects with unsafePerformIO
by Björn Peemöller 08 Apr '11

08 Apr '11

Hello, we have a strange performance behaviour when we use unsafePerformIO, at least with GHC 6.12.3 and 7.0.1. Please consider the example program following at the end of this post. Running the original code the execution time is about 26 seconds, while uncommenting one (or both) of the comments shrinks it to about 0.01 seconds on our machine. Is there an explanation for this effect? Regards, Bjoern -- --------------- module Main where import System.IO.Unsafe traverse [] = return () -- traverse (_:xs) = traverse xs traverse (_:xs) = traverse xs >> return () makeList 0 = [] -- makeList n = () : (makeList (n - 1)) makeList n = () : (unsafePerformIO . return) (makeList (n - 1)) main = traverse $ makeList (10^5)

4 5

dynamic loading with ghc api?
by Rob Nikander 08 Apr '11

08 Apr '11

Hi all, I'd like to load a value from a .o file. I've got... import ObjLink main = do initObjLinker loadObj "Thing.o" resolveObjs Just ptr <- lookupSymbol "Thing_value_closure" Is that the correct symbol to load for the name "value" in module "Thing"? And if so, how to I get the haskell value out of the Ptr that I get from lookupSymbol? I found some code to do it and it works value :: Int, but it seg faults if value :: Integer, or something more complex like a function. {-# LANGUAGE MagicHash #-} {-# LANGUAGE UnboxedTuples #-} ... let !(Ptr addr) = ptr in case addrToHValue# addr of (# hval #) -> hval Is there some documentation for this that I'm missing? I'm looking at haddock with just type signatures, like this: http://www.haskell.org/ghc/docs/7.0.3/html/libraries/ghc-7.0.3/ObjLink.html (I'm a haskell beginner.) thank you, Rob

2 3