<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">My query was in response to an earlier post claiming that ai was a Rational, which post he almost simultaneously said to ignore.<br><br>I've used GHC and like it better than Hugs, but the Fedora Linux package is humongous and I'm only on dialup right now.<br><br>I'm still not sure what some of the error messages I was getting were about. As I wrote the function I tried to be aware of what "mixed mode" operations were kosher ala<br><br>Main> 1 / (6%7)<br>7 % 6<br>Main> 1 - (6%7)<br>1 % 7<br>Main> (6%7) - 1<br>(-1) % 7<br>Main> <br><br>but still kept getting kicked out.<br><br>Better error messages certainly couldn't hurt.<br><br>Thanks.<br><br>Michael<br><br><br>--- On <b>Mon, 3/30/09, Ketil Malde <i><ketil@malde.org></i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>From:
Ketil Malde <ketil@malde.org><br>Subject: Re: [Haskell-cafe] Rational and % operator remix<br>To: "michael rice" <nowgate@yahoo.com><br>Cc: "Brandon S. Allbery KF8NH" <allbery@ece.cmu.edu>, haskell-cafe@haskell.org<br>Date: Monday, March 30, 2009, 2:48 AM<br><br><div class="plainMail">michael rice <<a ymailto="mailto:nowgate@yahoo.com" href="/mc/compose?to=nowgate@yahoo.com">nowgate@yahoo.com</a>> writes:<br><br>> cf2 :: Rational -> [Int]<br>> cf2 a = let ai = floor a <-- Doesn't this make ai an Int? -Michael<br>> in<br>> if a == (toRational ai)<br>> then [ai]<br>>
else ai : cf2 (1 / (a - ai))<br><br>One thing that you could try, is ghci in addition to (or instead of)<br>Hugs. That will give you another take on the error messages, where<br>Hugs says:<br><br>> Main> :load cf.hs<br>> ERROR "cf.hs":7 - Type error in application<br>> *** Expression : ai : cf2 (1 / (a - ai))<br>> *** Term : ai<br>> *** Type : Ratio Integer<br>> *** Does not match : Int<br><br>ghci will tell you:<br><br> Couldn't match expected type `Rational' against inferred type `Int'<br> In the second argument of `(-)', namely `ai'<br> In the second argument of `(/)', namely `(a - ai)'<br> In the first argument of `cf2', namely `(1 / (a -
ai))'<br><br>So while this is (almost) right:<br><br>> cf2 a = let ai = floor a <-- Doesn't this make ai an Int? -Michael<br><br>The problem is the subtraction of ai from a, which forces them to be<br>the same type. I tend to find ghc's messages more informative than<br>Hugs's (but perhaps it is just that I am more familiar with ghc?).<br><br>-k<br>-- <br>If I haven't seen further, it is by standing in the footprints of giants<br></div></blockquote></td></tr></table><br>