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Building a REST Client

Haskell on Reddit - Fri, 10/24/2014 - 2:56pm
Categories: Incoming News

Typing an AST without loosing the Applicative / Monad instances

Haskell on Reddit - Fri, 10/24/2014 - 10:06am


This is my expression tree and related combinators

I’d like to type it in order to typecheck at compile time so that I can’t, for instance, right an addition of a floating value and an integral value. With the current implementation, I use a nasty L (for litteral) data to represent typed values at runtime, which sucks to me since I have to write a function typecheck :: E a -> Maybe TypeError.

Any idea?

submitted by _skp
[link] [11 comments]
Categories: Incoming News

I have trust issues with Haskell, but I don't think they are justified.

Haskell on Reddit - Fri, 10/24/2014 - 8:23am

I have been a Haskell enthusiast for a while now, but haven't seriously committed to it on any large projects.

The combination of these things leads to this feeling:

  1. Though Haskell is used in some production settings, it doesn't have nearly the amount of use as the other languages/platforms I use.
  2. Sometimes things feel too easy. Like the fact that I don't have a thousand lines of framework setup and configuration. Or that I can just blindly put together things by their types and have them work.
  3. I don't really know what I would do if I ever did have a big problem, especially if this was for my individual business ventures (that is, no buckets of money to throw at the problem).

I am able to create software more easily, and it seems much more reliable, and this worries me.

Are these completely unfounded?

submitted by fear-of-flying
[link] [34 comments]
Categories: Incoming News

Project adoption proposals?

Haskell on Reddit - Fri, 10/24/2014 - 2:57am

It has recently been suggested to me that working with someone elses code might be a good way to break out of grown habits.

So I was thinking I will try to adopt an unmaintained project. Do you guys have any listings or proposals on which project might come in question? Other than that: Opinions on this idea?

Note: It's not that I have too much spare time, so I won't take on any projects that need a great amount of work to get to a usable state. More like embracing everything not invented here and try to work with what I get.

submitted by goliatskipson
[link] [7 comments]
Categories: Incoming News

Parse CSV / TSV file in Haskell - Unicode Characters

haskell-cafe - Fri, 10/24/2014 - 2:35am
Hi, I'm trying to parse a tab-delimited file using cassava/Data.Csv in Haskell. However, I get problems if there are "strange" (Unicode) characters in my CSV file. I'll get a parse error (endOfInput) then. According to the command-line tool "file", my file has a "UTF-8 Unicode text" decoding. My Haskell code looks like this: {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE OverloadedStrings #-} import qualified Data.ByteString as C import qualified System.IO.UTF8 as U import qualified Data.ByteString.UTF8 as UB import qualified Data.ByteString.Lazy.Char8 as DL import qualified Codec.Binary.UTF8.String as US import qualified Data.Text.Lazy.Encoding as EL import qualified Data.ByteString.Lazy as L import Data.Text.Encoding as E
Categories: Offsite Discussion

pattern matches are overlapped

haskell-cafe - Thu, 10/23/2014 - 7:23pm
This works fine keyboardAct a d p (SpecialKey KeyLeft) Down Modifiers {shift=Down, ctrl=Up, alt=Up} = do (x,y) <- get p p $= (x-0.1, y) This keyboardAct a d p (SpecialKey KeyLeft) Down shiftDown = do (x,y) <- get p p $= (x-0.1, y) where, shiftDown = Modifiers {shift=Down, ctrl=Up, alt=Up} gives me : KeyBindings.hs:32:1: Warning: Pattern match(es) are overlapped In an equation for `keyboardAct': keyboardAct angle delta p (SpecialKey KeyLeft) Down Modifiers {shift = Up, ctrl = Up, alt = Up} = ... keyboardAct is used several times via pattern matching, e.g. keyboardAct angle delta p (SpecialKey KeyLeft) Down Modifiers {shift=Up, ctrl=Up, alt=Up} = do (x,y) <- get p a <- get angle d <- get delta angle $= a+d and there are several more. So clearly, the pattern match is overlapped, just like the warning says. The question is why
Categories: Offsite Discussion

Danny Gratzer: Update on Old Projects

Planet Haskell - Thu, 10/23/2014 - 6:00pm
Posted on October 24, 2014 Tags: haskell, personal

All though most people I talk to know me for my blog, I do occasionally actually write software instead of just talking about it :)

Sadly, as a mercurial user most of my stuff has languished with on bitbucket. I’ve had a few people tell me that this is annoying for various reasons. Yesterday, I finally got around to fixing that!

As of yesterday, all of my interesting projects are mirrored on [github][my-github]. I’m still using mercurial but thanks to the lovely git-hg tool this is not an issue. You can fork, pull-request, or generally peek and poke as you please. From my end all of these actions look like nice mercurial changesets so I can continue to live under my rock where I don’t need to understand Git.

As a quick list of what haskell code is up there now

Which I think includes every project I’ve blogged about here as well as a few others. Sorry it took so long!

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Categories: Offsite Blogs

Are list comprehensions idiomatic in modern Haskell style?

Haskell on Reddit - Thu, 10/23/2014 - 4:15pm

I've been noticing dozens of recent Stack Overflow questions asking how to do things specifically with list comprehensions ("I want to write a function that uses list comprehensions...") ("I'm trying to use list comprehension to return the list elements that differ from the next.") or otherwise has a map or other operation shoehorned into a comprehension ("capitalise str = [ toUpper x | x <- str ]").

My assumption is that these are all telltales of homework assignments of the form "Using a list comprehension..." or just a teacher somewhere that's really partial to the sugar.

My sense is that list comprehensions in general are rarely idiomatic in "production" these days; rather, we prefer to use folds, map/fmap, scans, sometimes explicit recursion, or perhaps the monad with do. What's the community feeling on this topic?

submitted by conklech
[link] [51 comments]
Categories: Incoming News

acid-state problem.

haskell-cafe - Thu, 10/23/2014 - 9:06am
Hi, I have following code. In init, I called update, createCheckpoint, and close. So every time the code runs, if the DB did not exist, it would ask some configurations and create one. But actually it asks for init every time. How should I use it? state <- openLocalStateFrom dbFolder $ State ConfNone conf <- query state QueryState case conf of ConfNone -> init state m c -> process state m c
Categories: Offsite Discussion