Re: oops (was: Re: if-then-else inside a "do")

[Mark Carroll]

On Wed, 30 Jan 2002, Kevin Glynn wrote:

> I think the Haskell Wiki was going to be the place to collect
> interesting code fragments.
>
> However,  I must add that these functions are already part of the
> Haskell 98 standard.  See the Monad module in the Library Report.

Ah, cool, both points sound good. Thanks. (-:

-- Mark (still figuring out the wiki)


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Re: oops (was: Re: if-then-else inside a "do")

[Kevin Glynn]

I think the Haskell Wiki was going to be the place to collect
interesting code fragments.

However,  I must add that these functions are already part of the
Haskell 98 standard.  See the Monad module in the Library Report.

cheers
k



Mark Carroll writes:
 > On Wed, 30 Jan 2002, Bernard James POPE wrote:
 > (snip)
 > > when :: (Monad m) => Bool -> m () -> m ()
 > > when p s  = if p then s else return ()
 > >
 > > unless   :: (Monad m) => Bool -> m () -> m ()
 > > unless p s= when (not p) s
 > (snip)
 > 
 > That's cute. People post all sorts of handy little code fragments here.
 > Does anyone collect them together into a sort of "here's some useful stuff
 > that's worth looking at" library?
 > 
 > -- Mark
 > 
 > 
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Re: oops (was: Re: if-then-else inside a "do")

[Mark Carroll]

On Wed, 30 Jan 2002, Bernard James POPE wrote:
(snip)
> when :: (Monad m) => Bool -> m () -> m ()
> when p s  = if p then s else return ()
>
> unless   :: (Monad m) => Bool -> m () -> m ()
> unless p s= when (not p) s
(snip)

That's cute. People post all sorts of handy little code fragments here.
Does anyone collect them together into a sort of "here's some useful stuff
that's worth looking at" library?

-- Mark


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oops (was: Re: if-then-else inside a "do")

[Bernard James POPE]

Oops,

Thanks to Kevin who pointed out:

when :: (Monad m) => Bool -> m () -> m ()
when p s  = if p then s else return ()

unless   :: (Monad m) => Bool -> m () -> m ()
unless p s= when (not p) s


> So now I tend to use:
> 
>doIf :: Monad a => Bool -> [a b] -> a ()
>doIf b e = if b then sequence_ e else return ()

Bernie.

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