[Haskell-cafe] [ANNOUNCE] Penny - double-entry accounting
I'm pleased to make the first public announcement of the availability of Penny, a double-entry command-line accounting system. Penny is inspired by Ledger, an excellent program in its own right. Ledger's websites and sales pitches are much better developed than those for Penny, so first take a look at Ledger's website to see if the concepts behind this program interest you: http://www.ledger-cli.org/ With that in mind, here is what distinguishes Penny from Ledger: * Smarter report formatting. When using Ledger I rarely bothered to reformat the reports because I could never remember how to use the cryptic formatting strings. Penny automatically formats reports to fit the width of your screen. You can easily add or remove information in your reports. * Use of color. Color is baked into Penny, making reports easier to read. It takes advantage of 256-color terminals where available. * Adherence to double-entry accounting principles. Ledger will allow you to enter unbalanced transactions. Penny never allows this. Even infinitesimally unbalanced transactions will render your entire ledger invalid. * Different handling of commodities. In part because of the strict adherence to double-entry accounting principles, Penny handles commodities (e.g. transactions involving multiple currencies, or currency and equities) differently than Ledger. Some might regard Penny's handling of commodities to be a pain, but I think it results in a system that is more predictable, has no corner cases, and is easy to test. * More orthogonal command-line interface. For example, in Ledger, you use one set of options to filter postings by date, and a different set of options to control the dates of postings that are shown in the register report. Penny uses identical options for these two purposes; what these options mean depends on where they appear on the command line. In addition, in Penny you can build filtering expressions of arbitrary complexity, using either infix or reverse polish notation. * Automated import of postings. You can import postings from your bank as long as it gives you OFX files. Many financial institutions supply OFX files, as it is the format used by Quicken and by the now-defunct Microsoft Money. Penny can also help automate a great deal of the process of reconciling your ledger with bank statements. This removes an enormous amount of the drudgery that is associated with maintaining a ledger. * Exposes a Haskell API. This is actually the primary reason I wrote Penny. I run several automated checks on my ledger. Doing this in Ledger was growing difficult because I had no standalone parser for the ledger files. With Penny I can easily write additional small programs to check up on the consistency of my ledger (for instance, to make sure I'm not using invalid accounts, or to make sure that a particular account has postings within a given time period.) The power of Haskell makes this much easier than it would be if I used a dynamically typed language like Haskell or, as I used to do with Ledger, a random assemblage of shell, Awk scripts, Haskell, and more. Another child of Ledger that is written in Haskell is hledger: http://hledger.org/ hledger is a great program; if you like it, please continue using it. In addition to what you can glean from the bullets above, here are some key ways Penny differs from hledger: * hledger is at least partially compatible with Ledger; Penny is incompatible with Ledger. There currently is no program to convert Ledger files to the format Penny uses (I once wrote such a program to convert my Ledger files to Penny; after that the program was of no use to me and the file format has since changed, rendering that code useless.) * hledger has a web interface. Penny does not and I doubt it ever will. * hledger has a robust community; Penny does not. * hledger supports more of Ledger's feature set with features such as timelog support, periodic reports, and balance assertions. Penny does not have these features. * hledger uses floating-point types to represent amounts: http://hackage.haskell.org/package/hledger-lib-0.21.3/docs/Hledger-Data-Types.html#t:Quantity Penny uses only integers: http://hackage.haskell.org/package/penny-0.30.0.0/docs/Penny-Lincoln-Bits-Qty.html This page summarizes why that matters: http://stackoverflow.com/questions/3730019/why-not-use-double-or-float-to-represent-currency * Penny is BSD3; hledger is GPL. And an entirely subjective comparison that may be biased: Penny is designed from the ground up to use Haskell's static type system and its module system to its maximum advantage, which makes Penny easier to use as a base for your own programs to check your ledger, and which reduces bugs. Penny has been in development for over a year now, and I use it to maintain my financial records. A set of QuickCheck tests, in conjunction with maximum exploitation of Haskell's static type system, help ensure the correctness of the
Re: [Haskell-cafe] On Markdown in Haddock and why it's not going to happen
On Thu, Aug 29, 2013 at 9:30 PM, Mateusz Kowalczyk fuuze...@fuuzetsu.co.ukwrote: Greetings café, Perhaps some saddening news for Markdown fans out there. As you might remember, there was a fair amount of push for having Markdown as an alternate syntax for Haddock. This is a little off-topic, but the Haddock website apparently is years out of date. http://www.haskell.org/haddock/ says the latest version is 2.8.0 released in September 2010, but apparently I have 2.13.2 on my machine. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] loop error message
I compiled some code with GHC 7.6.3 that produces a simple error at runtime myProgramName: loop At which point the program exits with code 1. Is there documentation for this error anywhere? Does it mean I have some infinite loop in my code somewhere? If so, does GHC catch all infinite loops? I have never gotten this error before. Thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [ANNOUNCE] rainbow - print colored text on UNIX-like systems
Hi all, rainbow is a simple package to help you print colored text on UNIX-like systems. It's different from packages like terminfo (upon which it is based) and ansi-terminal in two ways. First, rainbow assumes you print text one chunk at a time. The properties of the terminal are reset with every chunk. That way you do not need to remember what the terminal's properties were before you print a new chunk. One chunk does not affect the next chunk. It's a state-free model that fits in well with functional programming. Second, rainbow makes it easy to use both 8- and 256-color terminals. Some sample things you can do in ghci: :set -XOverloadedStrings :m +System.Console.Rainbow putChunkLn $ Hello bold green world! f_green bold putChunkLn $ Red on 8-color, pink on 256-color f_red c256_f_201 mapM_ putChunk [green on blue f_green b_blue, , blue on green f_blue b_green, \n] So, add some color to things: http://hackage.haskell.org/package/rainbow ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Safe Haskell safe-inferred status
Is there a way to determine whether a module has been marked safe by GHC for purposes of Safe Haskell? The GHC 7.4 docs say that if I compile a module and I don't use the -XSafe or -XTrustworthy flag, GHC will automatically figure out whether the module would have compiled with -XSafe and, if so, marks the module as safe. Where does GHC record this determination? It doesn't seem to show up in ghc-pkg dump (there you can see trusted packages, but I am looking for safe-inferred status for modules.) ghc --show-iface seems to come up dry too. I know Haddock shows this information but sometimes it says Safe Haskell: None. I have no idea what this means so I was wondering what GHC itself says. Thanks. --Omari ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] cabal equivalent to make -k?
When using make (or, at least, GNU make) the -k option keeps going as far as possible after a compilation error. It's handy during developing--for instance, I know half of my code is busted, but I just want to see if this file compiles. Is there a similar way to do this with cabal? Thanks. --Omari ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Alex character sets
I'm wrinting (or at least, trying to write) an Alex lexer. Say I want to
group character ranges together and specify that I want a character that is
*not* in any of those ranges. Example
---
{
module Main where
}
%wrapper posn-bytestring
$lowAscii = \x00-\x1f -- unprintable stuff
$lowSymbol = \x21-\x2f -- exclamation point to solidus
$space = \x20
$special = [^$lowAscii $lowSymbol]
lex :-
$special { Word }
{
data Token = Word AlexPosn ByteString.ByteString
}
When I run this through Alex, I get Prelude.Enum.Char.pred: bad argument.
What am I doing wrong? How would I accomplish this sort of thing? Thanks.
--Omari
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Re: [Haskell-cafe] Alex character sets
OK, it turns out that having [^\x00] as a character range gives me the
error with pred. [\x00] works fine; [^\x00] gives the error message.
On Sat, Mar 24, 2012 at 6:33 PM, Omari Norman om...@smileystation.comwrote:
I'm wrinting (or at least, trying to write) an Alex lexer. Say I want to
group character ranges together and specify that I want a character that is
*not* in any of those ranges. Example
---
{
module Main where
}
%wrapper posn-bytestring
$lowAscii = \x00-\x1f -- unprintable stuff
$lowSymbol = \x21-\x2f -- exclamation point to solidus
$space = \x20
$special = [^$lowAscii $lowSymbol]
lex :-
$special { Word }
{
data Token = Word AlexPosn ByteString.ByteString
}
When I run this through Alex, I get Prelude.Enum.Char.pred: bad argument.
What am I doing wrong? How would I accomplish this sort of thing? Thanks.
--Omari
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[Haskell-cafe] Impact of try on Parsec performance
The Parsec documentation says that Parsec performs best on predictive grammars, and Parsec does not backtrack by default to improve performance (though this also improves error messages). On the other hand, I notice that attoparsec and polyparse backtrack by default, and attoparsec claims to be faster than Parsec (I can't remember if polyparse makes this claim). The Parsec documentation says there is a penalty for using try and suggests left-factoring grammars when possible. Real World Haskell says that excessive use of try can degrade Parsec performance quite significantly. On the other hand, some of the combinators provided with Parsec, such as notFollowedBy, use try. So my question is: what is the practical impact of using try? I ask because as a novice I have a simple grammar that could, perhaps, be factored to avoid use of try, but it's quite a brain puzzle for me and I wonder if it would ever be worth it. Does it matter how many characters try would have to store, or how often it would run? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] ANNOUNCE multiarg - parser combinators for command line parsing
On Mon, Jan 30, 2012 at 03:19:47PM +0100, Henning Thielemann wrote: On Sun, 29 Jan 2012, Simon Meier wrote: I'm currently using Neil Mitchell's cmdargs package [1]. How does your package compare to that? Last time I checked cmdargs it was not referential transparent. Is multiarg better in this respect? Absolutely, multiarg is 100% referentially transparent. The main data type in multiarg is a monad transformer, so if the programmer really wants to write something that does IO or is otherwise not referentially transparent, then she can. Certainly there is no need to do this though. I'd expect one would usually put the transformer on top of Identity, as I have always done so far. But the option is there if you want it. --Omari ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Text.Regex.Base throws exceptions with makeRegexOptsM
Hi folks, I'm using Text.Regex.Base with the TDFA and PCRE backends. I want to compile regular expressions first and make sure the patterns were actually valid, so I used makeRegexOptsM, which indicates a bad regular expression by calling fail. That allows you to use makeRegexOptsM with Maybe or with (Either String) (assuming that Either String is an instance of Monad, which of course is defined in Control.Monad.Error.) Doing this with Maybe Regex works like it should--bad pattern gives you a Nothing. But if you want to see the error message by using Either String, an exception gets thrown with the bad pattern, rather than getting a Left String. Why is this? Seems like an odd bug somewhere. I am a Haskell novice, but I looked at the code for Text.Regex.Base and for the TDFA and PCRE backends and there's nothing in there to suggest this kind of behavior--it should work with Either String. The attached code snippet demonstrates the problem. I'm on GHC 7.0.3 (though I also got the problem with 6.12.3) and regex-base-0.93.2 and regex-tdfa-1.1.8 and regex-pcre-0.94.2. Thanks very much for any tips or ideas. --Omari module Main where import Text.Regex.Base.RegexLike import Text.Regex.TDFA.String import Control.Monad.Error badPattern = [unclosed brace main = do let maybeRegex = makeRegexOptsM defaultCompOpt defaultExecOpt badPattern :: Maybe Regex -- This outputs Bad, no regex, as expected putStrLn $ maybe Good regex (const Bad, no regex) maybeRegex let eitherRegex = makeRegexOptsM defaultCompOpt defaultExecOpt badPattern :: Either String Regex -- This throws an exception, why? The whole point of -- using makeRegexOptsM is to not have exceptions. putStrLn $ either show (const Good regex) eitherRegex ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Text.Regex.Base throws exceptions with makeRegexOptsM
On Fri, Dec 30, 2011 at 01:24:02AM +0100, Daniel Fischer wrote: For Either, there used to be instance Error e = Monad (Either e) where ... fail s = Left (strMsg s) in mtl's Control.Monad.error, and all was fine if one used the regex functions with e.g. (Either String) as the Monad. Recently, however, it was decided to have instance Monad (Either e) where ... fail s = error s -- not explicitly, but by Monad's default method in Control.Monad.Instances. So now, if you have a pattern-match failure using (Either String), you don't get a nice 'Left message' but an error. Thanks so much, I would never have figured all this out. Spent a lot of time tonight rummaging through mtl and transformers and Control.Monad.Instances. Now, what can you do to get the equivalent of the old (Either String)? Use 'ErrorT String Identity'. This I tried. It turned out that it didn't work though and I had the same problem. I am guessing it is because my module has some imports at the top that are bringing the instances in Control.Monad.Instances into scope. Then it seems the Monad instance in Control.Monad.Instances (which is using the default fail, which calls error) is being used, rather than the instance from Control.Monad.Trans.Error. Only now do I really understand why orphan instances are bad: http://www.haskell.org/haskellwiki/Orphan_instance A simple fix for it all was to wrap Either in a newtype and then define a Monad instance for the newtype. --Omari ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haddock docs don't list instances
Web versions of Haddock documentation, even this old one, list a class's instances. http://www.haskell.org/ghc/docs/6.2.2/html/libraries/base/Prelude.html#5 My Haddock documentation does not have any class instances at all. This is true both of the documentation that comes with my Linux system (I use Debian) and of the documentation I generate locally using cabal-install or the Setup.hs program in my homemade packages. How do I get Haddock to make the instance lists? Anybody else have this problem--maybe it is a Debian bug? Thanks. --Omari -- Pay a little now, or pay a lot later. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why is toRational a method of Real?
Why is toRational a method of Real? I thought that real numbers need not be rational, such as the square root of two. Wouldn't it make more sense to have some sort of Rational typeclass with this method? Thanks. --Omari ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Regex multiple matches
Hi, How do I use Text.Regex.PCRE to get information on multiple matches? For instance, in ghci I get this error message: Prelude Text.Regex.PCRE foo =~ o :: [(Int,Int)] interactive:1:0: No instance for (RegexContext Regex [Char] [(Int, Int)]) arising from a use of `=~' at interactive:1:0-11 Possible fix: add an instance declaration for (RegexContext Regex [Char] [(Int, Int)]) In the expression: foo =~ o :: [(Int, Int)] In the definition of `it': it = foo =~ o :: [(Int, Int)] Real World Haskell's text suggests this should work, but the ghci output is littered with errors. http://book.realworldhaskell.org/read/efficient-file-processing-regular-expressions-and-file-name-matching.html Thanks for any help. Omari ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Regex multiple matches
How do I use Text.Regex.PCRE to get information on multiple matches? For instance, in ghci I get this error message: Prelude Text.Regex.PCRE foo =~ o :: [(Int,Int)] Solved; do getAllMatches (foo =~ o) :: [(Int, Int)] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
