- Haskell-Cafe - Haskell.org

Compilers book in Haskell
by Andrés Sicard-Ramírez 08 Apr '13

08 Apr '13

Juan, te puede interesar On Sat, Apr 6, 2013 at 5:56 PM, Sergey Bushnyak <sergey.bushnyak(a)sigrlami.eu > wrote: > I will recommend you book "Modern Compiler Design" by Dick Grune and > others. > Besides discussing different topics, authors use Haskell as example for > describing ideas behind compilers for functional language. > -- Andrés

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ANNOUNCE: binary-conduit-1.0
by Alexander V Vershilov 07 Apr '13

07 Apr '13

I'm happy to announce new binary-conduit [1] library, that's a serialization/deserialization library for using binary [2] package. [1] http://hackage.haskell.org/package/binary-conduit [2] http://hackage.haskell.org/package/binary -- Alexander

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ANNOUNCE: antiquoter-0.1.0.0
by L Corbijn 07 Apr '13

07 Apr '13

Hello cafe, I'm happy to announce the release of my first package antiquoter [1], a combinator library for writing quasiquoters and antiquoters. The main aim is to simplify their definitions and reduce copy-and-paste programming. The main feature the current version is trying to solve is code duplication in antiquoters. The problem for writing antiquoters is that it need to be done twice, once for use as an expression and once for use as a pattern. These two implementations are very similar, which leads to copy-and-paste programming. For a good example of what this leads to see the antiquoters of language-c-quote[2], where almost every antiquoter is written twice. A very simple example with the rewritten version is provided in the documentation [3]. Lars [1]:http://hackage.haskell.org/package/antiquoter [2]: http://hackage.haskell.org/packages/archive/language-c-quote/0.7.1/doc/html… [3]: http://hackage.haskell.org/packages/archive/antiquoter/0.1.0.0/doc/html/Lan… [4]:https://github.com/Laar/antiquoter

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Error when building executable with profiling enabled
by Nikolaos Bezirgiannis 07 Apr '13

07 Apr '13

Hello, i have an executable where i want to run profiling on. I do: ghc --make -prof -auto-all -fth Custom.hs but it does not built and the output is: bench\HLogo\Custom\Custom.hs:1:1: Dynamic linking required, but this is a non-standard build (eg. prof). You need to build the program twice: once the normal way, and then in the desired way using -osuf to set the object file suffix. I tried googling on the error with no success. What can I do to compile this file for profiling? Cheers, Nikos

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code-as-config, run-time checks and error locations
by Steffen Schuldenzucker 07 Apr '13

07 Apr '13

Dear Café, I'm working on a EDSL that will include both type checks (at compile time) and semantic checks (at run time). - Semantic properties are known at compile time but feel too complex to me to be encoded in the type system. If one of the runtime checks fails, I'd like to print the location of the error, i.e. not Error: Unknown field `AMOUNT' in table `ENTRIES' (where? why?) but Error: Unknown field `AMOUNT' in table `ENTRIES' Referenced at analysis1.hs:43:7 by `sumByInvoice' which was called at analysis1.hs:66:3 by `main' ENTRIES defined at analysis1.hs:13:8 I'm not yet sure which level of granularity I want for error messages and one can probably get arbitrarily fancy on this. For the moment I think it would be enough to auto-insert the location of calls to a certain set of functions. Any experience on this? Thanks a lot. -- Steffen

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Is there an escape from MonadState+MonadIO+MonadError monad stack?
by Ömer Sinan Ağacan 07 Apr '13

07 Apr '13

Hi, I'm a hobbyist Haskell programmer and my use of Haskell is mostly consists of writing interpreters, simple virtual machines, and type checkers. One thing I'm not happy about my Haskell programs is, almost all of my programs have a monad transformer stack consisting MonadError, MonadIO and MonadState. Let's say I'm writing an interpreter, I certainly need MonadIO to interpret object language's IO functions: printing, reading from file etc. I also need MonadState for, well, states(dynamic environment etc.). MonadError is also required because most computations can fail(unbound variable error, type mismatch etc. it can be also used for implementing exceptions in object language) Same applies for my other applications as well. Type checkers require MonadError(unification error etc.), MonadState(to keep substitutions). MonadIO is not required in this case. But it also required for virtual machines(IOVector for memory -- ST vectors also work, but IO is still required for other stuff - printing, display etc.) I know these are mostly related with my application area, but I still wanted to write this because I may be missing something, or simply doing things wrong. Advices from experienced Haskell programmers would be appreciated, Cheers, Ömer

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Re: [Haskell-cafe] Haskell is a declarative language? Let's see how easy it is to declare types of things.
by wren ng thornton 06 Apr '13

06 Apr '13

On 4/3/13 11:46 PM, Albert Y. C. Lai wrote: > On 13-04-03 07:39 PM, Alexander Solla wrote: >> There's your problem. Mathematicians do this specifically because it is >> helpful. If anything, explicit quantifiers and their interpretations >> are more complicated. People seem to naturally get how scoping works in >> mathematics until they have to figure out free and bound variables. > > Quantifiers are complicated, but I don't see how explicit is more so > than implicit. When the quantifiers are implicit, we can rely on the unique human ability to DWIM. This is a tremendous advantage when first teaching people about mathematical concerns from a logical perspective. However, once people move beyond the basics of quantification (i.e., schemata, rank-1 polymorphism, etc), things get really hairy and this has lead to no end of quibbles in philosophy and semantics, where people seem perversely attached to ill-specified and outdated logics. On the other hand, with explicit quantification you can't rely on DWIM and must teach people all the gritty details up front--- since the application of those details is being made explicit. This is an extremely difficult task for people who are new to symbolic reasoning/manipulation in the first place. In my experience, it's better to get people fluently comfortable with symbolic manipulations before even mentioning quantifiers. -- Live well, ~wren

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meaning of "referential transparency"
by Henning Thielemann 06 Apr '13

06 Apr '13

Can someone enlighten me about the origin of the term "referential transparency"? I can lookup the definition of "referential transparency" in the functional programming sense in the Haskell Wiki and I can lookup the meaning of "reference" and "transparency" in a dictionary, but I don't know why these words were chosen as name for this defined property.

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Fwd: meaning of "referential transparency"
by Alexander Solla 06 Apr '13

06 Apr '13

On Sat, Apr 6, 2013 at 10:43 AM, Henning Thielemann < lemming(a)henning-thielemann.de> wrote: > > Can someone enlighten me about the origin of the term "referential > transparency"? I can lookup the definition of "referential transparency" in > the functional programming sense in the Haskell Wiki and I can lookup the > meaning of "reference" and "transparency" in a dictionary, but I don't know > why these words were chosen as name for this defined property. > Willard V.O. Quine Referential transparency arises in constrast to referential opacity. A context is referentially opaque (reference can't "see" through the context) when the substitution of equal values are not necessarily equal. For example, quotation marks are referentially opaque: "It is necessary that four and four is eight" "The number of planets is eight" If these contexts were referentially transparent, we would find that "It is necessary that the number of planets is eight", a situation which at the very least puts us in a tight ontological position.

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ANNOUNCE: hydra-print-0.1.0.0
by Ryan Newton 06 Apr '13

06 Apr '13

Hello cafe, This is an NCurses front end for visualizing a dynamic collection of text streams (e.g. as produced by "make -j" or "cabal -j"). It just splits the window when more streams appear. http://hackage.haskell.org/package/hydra-print http://parfunk.blogspot.com/2013/04/hydra-print.html Right now I'm using it for the monad-par benchmark script, but I hope to provide a cabal patch soon. Cheers, -Ryan

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