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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)
----------------------------------------------------------------------
Message: 1
Date: Fri, 23 Jun 2017 09:58:35 -0400
From: David McBride <toa...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] help designing types for a gsl fit
Message-ID:
<can+tr42lkxcggzkvfzcsmxuk79t39f36_ena4cwdmp1px_g...@mail.gmail.com>
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
<alarre...@gmail.com> 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
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
------------------------------
Message: 2
Date: Fri, 23 Jun 2017 16:24:07 +0200
From: Silent Leaf <silent.le...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: [Haskell-beginners] What to use when you need random values?
Message-ID:
<cagfccjp6ai7x_n9+agqgggjgamwtqou-+ynsubdhaen4sp+...@mail.gmail.com>
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. :)
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Message: 3
Date: Fri, 23 Jun 2017 11:10:05 -0400
From: David McBride <toa...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] What to use when you need random
values?
Message-ID:
<CAN+Tr43UcOVbES4Sw9BdhuYuu-iYekc2nsCxT0tx5nKp2uTM=g...@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
When you are unsure about the differences between functions, it can be
good to read the haddocks for the library.
http://hackage.haskell.org/package/random-1.1/docs/System-Random.html
The standard haskell random library supports the idea of splitting a
seed randomly. You take one seed and split it, and now you have two
seeds, which will each generate different randoms independently.
getStdGen gets the current global seed. newStdGen splits new a seed
off of the current global seed. mkStdGen allows you to create a seed
from a value so that you can get the same set of randoms repeatedly.
I would say if you are in IO, just use randomRIO. If you are in
monadic code that not IO at its base, you should use MonadRandom
library on hackage. Quickcheck randomness is only really used in
quickcheck, although it is probably based off the standard libraries.
Just keep in mind that randomness is a concept that is a little hard
to wrap your head around in haskell until you've been using it a
little while.
On Fri, Jun 23, 2017 at 10:24 AM, Silent Leaf <silent.le...@gmail.com> wrote:
> 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.
> :)
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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