[Haskell-beginners] making function problem (chapter 6 of Programming in Haskell)

[Roelof Wobben]

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> Subject: RE: [Haskell-beginners] making function problem (chapter 6 of Programming in Haskell)
> From: ds at iai.uni-bonn.de
> To: rwobben at hotmail.com
> Date: Tue, 9 Aug 2011 15:33:19 +0200
>
> On Tue, 2011-08-09 at 13:15 +0000, Roelof Wobben wrote:
> > Lets make a try
> >
> >
> >
> > ( ^) :: Int -> Int -> Int
> >
> > ^ x 0 = 1
> >
> > ^ x y = x + x ^ (y-1)
> >
> nearly perfekt, only syntax for (^) is still not ok. You would have
> noticed when compiling.
> The "^" is by default infix (like "+"), because its a symbol and not
> starting with a letter (the exact specification you can look up in your
> book I think, or in the Haskell report).
> If you want to use is prefix, like a "normal" function, then you have to
> put it in brackets, ie. write (^).
> So either write
>
> (^) x 0 = 1
> (^) x y = x * (x ^ (y-1))
>
> or (I think this works as well)
>
> x ^ 0 = 1
> x ^ y = x * (x ^ (y-1))
>
> Please notice also the extra brackets around x ^ (y-1) in my definition.
> You may not know the precedence of * and ^.
> If you eliminate the brackets, make sure you gave the right priority to
> ^, that the program does not calculate (x * x) ^ (y-1).
>
> And, last but not least a second typo: why do you use "+" in your
> definition of the power?
>


because of this 

 

4 * 3 = 4 + 4 + 4 

 

so the forumala on the second run would be  4 + 4* 3 

 

 

Roelof