April 2013 - Haskell-Cafe

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

3 3

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

3 5

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

5 7

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

4 5

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.

6 6

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.

1 0

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

2 1

Haskell is a declarative language? Let's see how easy it is to declare types of things.
by Johannes Waldmann 05 Apr '13

05 Apr '13

I absolutely love to use Haskell when teaching (and I have several years of experience doing it). And I absolutely dislike it when I have to jump through hoops to declare types in the most correct way, and in the most natural places. This is hard to sell to the students. - Examples: 1. for explicit declaration of type variables, as in reverse :: forall (a :: *) . [a] -> [a] I have to switch on RankNTypes and/or KindSignatures (ghc suggests). C'mon, this has nothing to do with ranks per se. It's a type of a very simple function! IMHO even Java/C# do this better (with slightly strange syntax, but at least you get to declare the type variable). 2. for declaring types of local variables, as in \ (xs :: [Bool]) -> ... I have to enable PatternSignatures (actually ghc suggests ScopedTypeVariables but again there is no type variable in sight) I need to do this often, to disambiguate properties for Smallcheck. All of this just because it seemed, at some time, a clever idea to allow the programmer to omit quantifiers? (I know, mathematicians do this all over the place, but it is never helpful, and especially not when teaching.) I think that (1) implies (2): there could be no ambiguity about scopes (of typevars in patterns) if each typevar had to be introduced by explicit quantification. Then (in a pattern signature) a use could be distinguished from a declaration. Yes, the above is a rant. I can achieve what I want with some ghc options, and perhaps my point is that these should be on by default - or have better names, because presently, they are unintelligible to the (beginner) student.

8 14

Haskell and WinRT
by Mark Flamer 04 Apr '13

04 Apr '13

There was a short thread on this in the beginners section a while back. I think it is an exciting subject and would like to hear what others thoughts are on it. The Windows 8 metro style apps are built using a new API that is designed to be exposed to other languages using "language projections" which are a thin wrapper around the windows runtime. Microsoft has provided these for C#, C++, Javascript & HTML and is encouraging language developers to create them for other languages. This seems like it might be the easiest rout to getting Haskell apps on tablets etc. with a modern UI. Simon Marlow discusses it briefly on this <https://plus.google.com/107890464054636586545/posts/PuFPongpyR4> page and there is a video on the topic here <http://channel9.msdn.com/Events/Lang-NEXT/Lang-NEXT-2012/The-Windows-Runtime> . Might even be a good summer of code project for someone. -- View this message in context: http://haskell.1045720.n5.nabble.com/Haskell-and-WinRT-tp5728106.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

1 0

Functional Programming Internship @ Intel
by Levent Erkok 04 Apr '13

04 Apr '13

[I'm posting on behalf of my colleague Jesse Bingham. While Jesse and I work for different groups at Intel, we collaborate quite often, and I do expect to work with the intern to an extent as well. To that end, I'm happy to answer any questions you might have. Otherwise, direct all correspondence to Jesse as indicated below. -Levent.] ================================================================= Hi, we are looking to hire an intern to fill the below position. If interested, please send your resume to jesse.d.bingham(a)intel.com. Thanks Intern SW Engr. Formal Verification - 708053 Description Design and Technology Solutions (DTS) creates the software that caters to Intel's insatiable appetite for innovating silicon technology. Through our CAD solutions and engineering services, we enable Intel's process engineers to achieve the technical breakthroughs required to deliver tomorrows technology, and we help Intel's architects and chip designers develop products that change the world. To us, Moore's law is the imperative that drives our work to continuously improve the ways we explore technology options, so we can deliver better products, faster. As a software engineer in DTS, you will work as part of a multi-disciplinary team to create software tools that meet Intel's specific, rapidly evolving requirements for designing, manufacturing, testing, and packaging silicon products. We work very closely with process engineers and chip designers (our internal customers) around the world, to understand their technical challenges, and to create proprietary CAD solutions. We help them apply our software to answer critical questions, and to address their design and manufacturing objectives. The daily work in DTS spans the complete software life cycle, from early research to mature production code with industrial robustness and quality. To deliver critical new features in our established solutions, or to create new CAD capabilities beyond the state of art in the industry, our teams frequently go through all steps in software development - problem analysis, requirements definition, design, coding, test, and deployment. As a member of our team, you are expected to participate actively in all these steps. Success in this fast-paced, results-oriented environment requires strong analytical skills and the ability to perform productive teamwork, which depends on very good communication skills. In this particular job opening, you will join DTS's Formal Verification Center of Expertise (FVCoE) for a three month placement in Hillsboro, Oregon, in the timeframe of fall 2013. A primary responsibility of FVCoE is the maintenance of a large code base used for formal verification of Intel's core datapath designs; you will help rework several key aspects of this code to make it more robust and user-friendly. This will involve strict software engineering discipline to deliver robust, quality code that must perform reliably and predictably, The code is written in an in-house functional language called reflect. Reflect is similar to the popular functional languages Ocaml and Haskell; hence you should have considerable experience with one of these. Experience with formal verification is preferred but not necessarily required. Applicants will ideally be working towards a graduate degree in Computer Science or a related discipline. Qualifications Minimum Requirements Skills: Functional programming coding skills; experience with one or more scripting languages; analytical skills for problem abstraction; broad theoretical knowledge in computer science, including algorithms and data structures; familiarity with standard software engineering practices. Experience: acquired through coursework, internships, or personal projects. Experience in applied computer programming in a functional language. Education: working toward an MS or Ph.D. degree in Computer Science, Applied Mathematics, or in an Engineering field related to silicon technology. Strong senior undergraduates will also be considered. Preferred Requirements Skills: Familiarity with: hardware formal verification techniques (especially symbolic simulation, binary decision diagrams, parametric substitutions, case splitting), arithmetic/floating point computer hardware designs, IEEE 754 floating point standard, Intel x86 instruction set.

1 0