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在 2017年6月24日，20:00，beginners-request@haskell.org 写道：

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Today's Topics:

1. Re: help designing types for a gsl fit (David McBride) 2. What to use when you need random values? (Silent Leaf) 3. Re: What to use when you need random values? (David McBride)

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Message: 1 Date: Fri, 23 Jun 2017 09:58:35 -0400 From: David McBride To: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell Subject: Re: [Haskell-beginners] help designing types for a gsl fit Message-ID: Content-Type: text/plain; charset="UTF-8"

If you look at the type of labelNew

GlibString string => Maybe string -> IO Label

If you look at the instances for GlibString, they could be Text or [Char]. You have to decide which. The fact that you are using Nothing does not tell you the entire final type. It could be Maybe [Char], or Maybe Text. Even though the choice seems arbitrary in this instance, you have to decide which it is. So try this.

lprog <- G.labelNew (Nothing :: Maybe [Char])

On Fri, Jun 23, 2017 at 3:22 AM, Agustin Larreinegabe wrote:

...

Hello, I'm trying to install an application Termite - Debug but I get this error in line 929:14

when it try to do this

lprog <- G.labelNew Nothing

The error says:

Could not deduce (glib-0.13.4.1:System.Glib.UTFString.GlibString string0) arising from a use of ‘G.labelNew’ from the context (D.Rel c v a s) bound by the type signature for sourceWindowCreate :: D.Rel c v a s => RSourceView c a u -> IO G.Widget at Debug/SourceView.hs:913:23-73 instance glib-0.13.4.1:System.Glib.UTFString.GlibString [Char] -- Defined in ‘glib-0.13.4.1:System.Glib.UTFString’ In a stmt of a 'do' block: lprog <- G.labelNew Nothing In the expression: do { vbox <- G.vBoxNew False 0; G.widgetShow vbox; spec <- getIORef svInputSpec ref; code <- codeWinNew spec; .... } In an equation for ‘sourceWindowCreate’: sourceWindowCreate ref = do { vbox <- G.vBoxNew False 0; G.widgetShow vbox; spec <- getIORef svInputSpec ref; cabal: Error: some packages failed to install:

I really don't know how to proceed, I'm new with Haskell

Thanks in advance.

----------------- Agustin Larreinegabe

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Message: 2 Date: Fri, 23 Jun 2017 16:24:07 +0200 From: Silent Leaf To: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell Subject: [Haskell-beginners] What to use when you need random values? Message-ID: Content-Type: text/plain; charset="utf-8"

Hi, I've had trouble finding the best way(s) to use random values in haskell, as it seems like there are several modules that either do the same thing or reuse one another i'm not sure.

There is System.Random - is it better to use the streams random(R)s or a more imperative randomRIO? - is it better to use mkStdGen or newStdGen or getStdGen? There is Test.QuickCheck and its type(class?) Gen There is a module in Control.Monad (i think) which exports the type Rnd

What about performances, and all those options? What do you like to use with random numbers?

I know that's a lot of questions. feel free to only answer to a few of them. :)