August 2018 - Haskell-Cafe

How to turn Integer into Proxy (n :: KnownNat) with n equal to the integer?
by David Banas 03 Aug '18

03 Aug '18

I’d like to use Data.Vector.Sized.slice’, but it wants the starting position and length parameters as Proxys, not Integers. How can I convert an Integer into a Proxy (n :: KnownNat) with n equal to the integer?

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[random-fu] sampleRVar with StdGen in RWS?
by Sergiu Ivanov 03 Aug '18

03 Aug '18

Dear Café, I would like to use random-fu to do some pseudo-random simulations for a given StdGen (so that I can run the same simulation multiple times, if needed). The following works: testState :: StdGen -> Int testState = evalState (sampleRVar $ uniform 1 10) The following doesn't: testRWS :: StdGen -> Int testRWS = fst . evalRWS (sampleRVar $ uniform 1 10) () I get <interactive>:2:26: error: • No instance for (MonadRandom (RWST () b0 StdGen Identity)) arising from a use of ‘sampleRVar’ • In the first argument of ‘evalRWS’, namely ‘(sampleRVar $ uniform 1 10)’ In the second argument of ‘(.)’, namely ‘evalRWS (sampleRVar $ uniform 1 10) ()’ In the expression: fst . evalRWS (sampleRVar $ uniform 1 10) () Indeed, I do see a MonadRandom instance for StateT, but none for RWST [0]. Is there a reason to not have a MonadRandom instance for RWST? Am I looking in the wrong place? - Sergiu [0] https://hackage.haskell.org/package/random-source-0.3.0.6/docs/Data-Random-…

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hp2pretty-0.9
by Claude Heiland-Allen 02 Aug '18

02 Aug '18

Hi all, hp2pretty[0] graphs heap profiles as SVG, much like hp2ps graphs as PostScript. I release hp2pretty-0.9[1], with support for detached keys in a separate text file with individual label images, which lets you construct a single key for multiple graphs, and also workaround the issue of truncated names (running off the edge of the image) when using the +RTS -L option. I applied the same principle to the titles, they can now be omitted from the images and added as captions in a surrounding document if desired. The examples/ folder shows how to embed the output in PDF[2] using the LaTeX 'svg' package (which calls out to 'inkscape'). There's also an HTML5[3] example. Because one can now create PDF output from SVG, the vapourware plans for other output formats have been dropped. Get it from Hackage[4], use `cabal unpack hp2pretty` to access examples. Or browse the git repository[5]. Thanks, Claude [0] https://mathr.co.uk/blog/hp2pretty.html [1] https://mathr.co.uk/blog/2018-08-01_hp2pretty-0.9_released.html [2] https://mathr.co.uk/hp2pretty/0.9/report.pdf [3] https://mathr.co.uk/hp2pretty/0.9/report.html [4] https://hackage.haskell.org/package/hp2pretty [5] https://code.mathr.co.uk/hp2pretty -- https://mathr.co.uk

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why different type variables enforce different types?
by Rui Azevedo 02 Aug '18

02 Aug '18

after using haskell for a while i was surprised by this little thing f::a->b f a=a and this is not making sense to me till now, so please can someone enlighten me, why does haskell assume that b can not be the same type of a? after all having two distinct math variables does not mean they can not have the same value. I know i could use f::a->a, but its not the same thing, on this last case I'm requesting them to be the same type, but on the first I'm not forbidding it, is there a math reason behind it? would type inference be rendered impossible if considering the case of them being equal? thanks Rui Azevedo (neu-rah)

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JOB | Permanent Java Developer (Montreal, Canada)
by James Tobin 01 Aug '18

01 Aug '18

Hello, I'm working with an employer that is looking to hire (for their Montreal office) a permanent Java developer that has extensive hands-on Java coding experience. Consequently I had hoped that some members of this mailing list may like to discuss with me further; off-list. I can be reached using "JamesBTobin (at) Gmail (dot) Com". Kind regards, James

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JOB | Permanent Java Development Manager (Montreal, Canada)
by James Tobin 01 Aug '18

01 Aug '18

Hello, I'm working with an employer that is looking to hire (for their Montreal office) a permanent development manager that has extensive hands-on Java coding experience. Consequently I had hoped that some members of this mailing list may like to discuss with me further; off-list. I can be reached using "JamesBTobin (at) Gmail (dot) Com". Kind regards, James

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