<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">Thank guys,<br><br>Now what am I misunderstanding in the code below?<br><br>I would think that<br><br>*Main> comb (Just 65) foo<br><br>and<br><br>*Main> comb (lookup 'A' lst) foo<br><br>would return the same result<br><br>Just 'A'<br><br><br>Michael<br><br>===========Haskell code=============<br><br>import Data.Char<br><br>lst = [('A',65),('B',66),('C',67),('D',68)]<br><br>-- comb is a combinator for sequencing operations that return Maybe<br>comb :: Maybe a -> (a -> Maybe b) -> Maybe b<br>comb Nothing _ = Nothing<br>comb (Just x) f = f x<br><br>foo :: Int -> Maybe Char<br>foo n = Just (chr n) <br><br>================Ghci===========<br><br>[michael@localhost ~]$ ghci<br>GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help<br>Loading package ghc-prim ... linking ... done.<br>Loading package integer ... linking ...
done.<br>Loading package base ... linking ... done.<br>Prelude> :load test1<br>[1 of 1] Compiling Main ( test1.hs, interpreted )<br>Ok, modules loaded: Main.<br>*Main> comb (Just 65) foo<br>Just 'A'<br>*Main> comb Nothing foo<br>Nothing<br>*Main> lookup 'A' lst<br>Just 65<br>*Main> (lookup 'A' lst)<br>Just 65<br>*Main> comb (lookup 'A' lst) foo<br><br><interactive>:1:22:<br> Couldn't match expected type `Integer' against inferred type `Int'<br> In the second argument of `comb', namely `foo'<br> In the expression: comb (lookup 'A' lst) foo<br> In the definition of `it': it = comb (lookup 'A' lst) foo<br>*Main> <br><br>--- On <b>Tue, 4/28/09, Lennart Augustsson <i><lennart.augustsson@gmail.com></i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255);
margin-left: 5px; padding-left: 5px;"><br>From: Lennart Augustsson <lennart.augustsson@gmail.com><br>Subject: Re: [Haskell-cafe] chr/ord?<br>To: "Tim Wawrzynczak" <inforichland@gmail.com><br>Cc: "michael rice" <nowgate@yahoo.com>, "haskell-cafe@haskell.org" <haskell-cafe@haskell.org><br>Date: Tuesday, April 28, 2009, 10:53 PM<br><br><div id="yiv1168158711"><div>You can also use the more general toEnum and fromEnum. <br><br> -- Lennart (iPhone)</div><div><br>On Apr 29, 2009, at 2:13, Tim Wawrzynczak <<a rel="nofollow" ymailto="mailto:inforichland@gmail.com" target="_blank" href="/mc/compose?to=inforichland@gmail.com">inforichland@gmail.com</a>> wrote:<br><br></div><div></div><blockquote type="cite"><div>Michael, those functions are not in the Prelude, they're in Data.Char.<br><br><div class="gmail_quote">On Tue, Apr 28, 2009 at 8:08 PM, michael rice <span dir="ltr"><<a rel="nofollow"
ymailto="mailto:nowgate@yahoo.com" target="_blank" href="/mc/compose?to=nowgate@yahoo.com"></a><a rel="nofollow" ymailto="mailto:nowgate@yahoo.com" target="_blank" href="/mc/compose?to=nowgate@yahoo.com">nowgate@yahoo.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><table border="0" cellpadding="0" cellspacing="0"><tbody><tr><td style="font-family: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; font-size: inherit; line-height: inherit; font-size-adjust: inherit; font-stretch: inherit;" valign="top">
Hi,<br><br>My Prelude docs must be out of date because chr and ord don't seem to be there. How do I access these functions?<br><br>Michael<br><br>===============<br><br>[michael@localhost ~]$ ghci<br>GHCi, version 6.10.1: <a rel="nofollow" target="_blank" href="http://www.haskell.org/ghc/"></a><a rel="nofollow" target="_blank" href="http://www.haskell.org/ghc/">http://www.haskell.org/ghc/</a> :? for help<br>
Loading package ghc-prim ... linking ... done.<br>Loading package integer ... linking ... done.<br>Loading package base ... linking ... done.<br>Prelude> chr 65<br><br><interactive>:1:0: Not in scope: `chr'<br>
Prelude> ord 'A'<br><br><interactive>:1:0: Not in scope: `ord'<br>Prelude> <br><br><br><br><br></td></tr></tbody></table><br>
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