September 2003 - Haskell-Cafe

Standalone Parser for Haskell Grammar
by Peter Robinson 10 Sep '03

10 Sep '03

Hello! Does anyone know a reasonable standalone Parser for the Haskell Grammar? The only one i found was hsparser but it's still an alpha release and i get a few errors during compiling. I know i could write one using Happy but i don't want to reinvent the wheel... regards Peter

3 2

Prefix and postfix operators
by Eugene Nonko 09 Sep '03

09 Sep '03

Hello, Are there any plans to extend Haskell parser to support prefix and postfix operators? It will be just great for domain-specific languages. It always kind of bothered me that unary minus is special. Thanks, Eugene

4 3

Why not haskell?
by Nick Name 09 Sep '03

09 Sep '03

Inspired by the various replies to the "haskell for non-haskell sake" I wonder why so much people uses haskell "only for prototipying" or producing code in other languages. I am just curios to hear from people who do not use haskell for project releases, or just think it's not suitable for a mature project, what exactly they find bad in current haskell implementations, or perhaps in the standard. Vincenzo

4 3

Library documentation
by Konrad Hinsen 05 Sep '03

05 Sep '03

Is there any place where I can find an introductory documentation for the Haskell libraries? To be more concrete, say I am interested in using Data.Array.ST.STUArray. I would need some explanation of the ST monad, and then an explanation of how I can use an STUArray in an ST monad. Plus ideally examples. But the same applies to most of the libraries. I can't find any documentation other than the very terse reference or the parts that happen to be covered by textbooks. Konrad.

3 2

RE: haskell reify, was sequencing data structures
by Simon Marlow 05 Sep '03

05 Sep '03

> I wonder whether keeping the names of data constructors in info tables > is expensive? > > I would have guessed not. (more debugging info such as > function names and src locations is likely to be more > expensive however). > > Anyway, would it be possible/feasible for GHC to keep names > in info tables > all the time, not just for profiling? At least for data-constructors? That's a distinct possibility. If you send patches we'll incorporate them. Cheers, Simon

1 0

RE: haskell reify, was sequencing data structures
by Simon Marlow 05 Sep '03

05 Sep '03

> - There needs to be some support from the > compilers/interpreters. Hugs > already has this. Ghc has some of it, but I abuse the > profiling system > in order to get the names of constructors to be present > on the heap. > I'm not happy with this. Under normal compilation GHC > doesn't keep > constructor names around, as far as I know. However, the > new debugger > in GHC must do something to get names of things, so perhaps the > -prof hack is no longer needed? I believe the debugger that Robert Ennals is working on tries to infer constructor names from the symbol table of the binary. Personally, I'd like to see debugging info placed in a separate segment of the binary, so it won't be loaded with the code but can be used by a debugger. Cheers, Simon

2 1

haskell html-colorizer
by henning＠ikso.net 04 Sep '03

04 Sep '03

Are anyone aware of a haskell html-colorizer a' la the emacs-mode? Regards /Henning

8 7

Problem with Infinite Lists
by Wamberto Vasconcelos 03 Sep '03

03 Sep '03

Folks I am new in this forum, so apologies if this has been asked before. If this is the case, please point me to the direction of the answer and I won't bother you again! Also, could you make sure you CC your answers to me? I am not sure how long it takes for my subscription to be activated and I don't want to miss out on the action :-) The Problem I have defined this function to calculate the Fibonacci numbers: all_fib :: [Float] all_fib = 1:(1:(add_fib all_fib)) where add_fib (x:y:rs) = (x + y):(add_fib (y:rs)) Which seems to work: Main> take 20 all_fib [1.0,1.0,2.0,3.0,5.0,8.0,13.0,21.0,34.0,55.0,89.0,144.0,233.0,377.0, 610.0,987.0,1597.0,2584.0,4181.0,6765.0] However, when I tried Main> filter even (take 20 all_fib) ERROR - Illegal Haskell 98 class constraint in inferred type *** Expression : filter even (take 20 all_fib) *** Type : Integral Float => [Float] What is going on here? Thanks in advance for any help/hint. -- Wamberto Vasconcelos, PhD wvasconcelos(a)acm.org Department of Computing Science http://www.csd.abdn.ac.uk/~wvasconc University of Aberdeen, Aberdeen AB24 3UE, Scotland, UK Phone +44 (0)1224 272283 Fax +44 (0)1224 273422

5 4

Histograms
by Konrad Hinsen 03 Sep '03

03 Sep '03

How would one best (read: most efficiently) create a histogram in Haskell? More precisely, given a list of integers in a known range, I want a count of how often any given number occurs. In imperative languages this would be done by iterating over the list and updating the count for the element under consideration. Without updatable data structures, the most straightforward solution I can think of would start by sorting the list, but for a long list that is very inefficient. Any suggestions? Konrad.

2 1

OT - Book on Programming
by Matthew Donadio 03 Sep '03

03 Sep '03

Hi all, This is a little off-topic, but I know there are a lot of people here with teaching experience. I am looking for a good book on programming. I recently picked up a gig doing ActionScript programming for a multimedia company. They have very good designers, but not very good programmers. So, they decided to hire a professional programmer to help them out with some of their projects. They have several people in the company who understand the mechanics of programming, but don't really understand the concepts. I am looking for a book to recommend to them. I would really like to find a book that just discusses programming, and avoids any one particular language. It would have to cover the common imperative controls, as well as basic data structures. Thanks. -- Matthew Donadio (m.p.donadio(a)ieee.org)

4 3