Re: [Haskell-beginners] making function problem (chapter 6 of Programming in Haskell)
----------------------------------------
Subject: RE: [Haskell-beginners] making function problem (chapter 6 of Programming in Haskell) From: ds@iai.uni-bonn.de To: rwobben@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
On Tue, 2011-08-09 at 13:37 +0000, Roelof Wobben wrote:
----------------------------------------
Subject: RE: [Haskell-beginners] making function problem (chapter 6 of Programming in Haskell) From: ds@iai.uni-bonn.de To: rwobben@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
Ok, I thought just the name of the function was a bit misleading, because "positivePower" should have been named "product". The power function is: 4 ^ 3 = 4 * 4 * 4 and the special case (if you want to handle 0 and not 1 as base case) 4 ^ 0 = 1 Cheers, Daniel.
participants (2)
-
Daniel Seidel -
Roelof Wobben