[Haskell-cafe] haltavista - look for functions by example

[Paul Brauner]

It works:

brauner at worf:/tmp$ cat test.hs 
import Test.QuickCheck
import Test.QuickCheck.Arbitrary
import Control.Monad(forM_)

intMul :: Integer -> Integer -> Integer
intMul x n | n <  0 = -(intMul x $ abs n)
           | n == 0 = 0
           | n >  0 = x + intMul x (n - 1)

main = do xs <- sample' arbitrary
          ys <- sample' arbitrary
          zip xs ys `forM_` \(x,y) -> 
            putStrLn (show x ++ " " ++ show y ++ " " ++ (show $ intMul x y))


brauner at worf:/tmp$ runghc test.hs | haltavista 
Prelude (*)

I will include this functionality in the next version. Thank you for
this nice idea.

Paul

On Sun, Sep 19, 2010 at 08:16:08PM +0200, Paul Brauner wrote:
> That's a great idea!
> 
> In the same vein, have you had a look at quickspec by Koen Claessen,
> Nicholas Smallbone and John Hughes?
> 
> www.cse.chalmers.se/~nicsma/quickspec.pdf
> 
> This reminds me of another idea, suggested by Jun inoue: look for
> functions by specification instead of examples.
> 
> I will try your idea ASAP. As you say, I think that might be helpful for
> beginners, as you suggest, or even when you're not a beginner anymore
> but you start using a new library.
> 
> Paul
> 
> 
> On Sun, Sep 19, 2010 at 07:41:21PM +0200, Roel van Dijk wrote:
> > Very interesting!
> > 
> > It got me thinking: if you combine this with the Arbitrary class [1]
> > of QuickCheck you can use it check if you have defined a function that
> > is "equal" to an already defined function.
> > 
> > Let's say I write the following function:
> > 
> >   intMul ∷ Integer → Integer → Integer
> >   intMul x 0 = 0
> >   intMul x n = x + intMul x (n - 1)
> > 
> > No you can automatically apply this function to a list of 100
> > generated inputs to get a list of input output pairs. Feed this into
> > haltavista and it should tell you that you can replace your definition
> > with Prelude (*). While such an observation is certainly not a proof
> > it is still useful.
> > 
> > It would be a nice addition to a Haskell editor. Especially for those
> > new to the language.
> > 
> > Regards,
> > Roel
> > 
> > 1 - http://hackage.haskell.org/packages/archive/QuickCheck/2.3/doc/html/Test-QuickCheck-Arbitrary.html