I am having difficulty in evaluating conditionals where more than one case is true. I require a program to express the following conditions: 1) x is faster than y if x is a buffolo and y is a pig. 2) x is faster than y if x is a pig and y is a slug. Both of these conditions are true (expressed in fact predicate). I include my attempt using guards (I have also tried case/if-then-else) I can apreciate that the program works when the first guard condition is met (faster Bob Joe). I am not sure why it fails on the second case (faster Bob Joe) Can I program the requirement using conditionals? Can I pattern match is some way? Is there another way to encode the requirement. Regards, Pat data E = Bob | Joe | Steve | Buffalo | Pig | Slug deriving Show fact Buffalo Bob = True fact Pig Joe = True fact Slug Steve = True faster x y | fact Buffalo x && fact Pig y = True | fact Pig x && fact Slug y = True | otherwise = False -- faster Bob Joe OK -- faster Steve Bob ***Exception: Faster.hs:(5,1)-(7,23): Non-exhaustive patterns in function fact This email originated from DIT. If you received this email in error, please delete it from your system. Please note that if you are not the named addressee, disclosing, copying, distributing or taking any action based on the contents of this email or attachments is prohibited. www.dit.ie Is ó ITBÁC a tháinig an ríomhphost seo. Má fuair tú an ríomhphost seo trí earráid, scrios de do chóras é le do thoil. Tabhair ar aird, mura tú an seolaí ainmnithe, go bhfuil dianchosc ar aon nochtadh, aon chóipeáil, aon dáileadh nó ar aon ghníomh a dhéanfar bunaithe ar an ábhar atá sa ríomhphost nó sna hiatáin seo. www.dit.ie Tá ITBÁC ag aistriú go Gráinseach Ghormáin – DIT is on the move to Grangegorman _______________________________________________ Beginners mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners |
On Mon, Apr 17, 2017 at 11:26:07AM +0100, PATRICK BROWNE wrote:
> I can apreciate that the program works when the first guard condition is > met (faster Bob Joe). > I am not sure why it fails on the second case (faster Bob Joe) Your `fact` function is the one that is partial fact Buffalo Bob = True fact Pig Joe = True fact Slug Steve = True -- what if all those patterns fail? You should add a line to handle "every other case", like fact Buffalo Bob = True fact Pig Joe = True fact Slug Steve = True fact _ _ = False Does that help? _______________________________________________ Beginners mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners |
Francesco, Yes, what I was looking for. Thanks, Pat On 17 April 2017 at 11:54, Francesco Ariis <[hidden email]> wrote: On Mon, Apr 17, 2017 at 11:26:07AM +0100, PATRICK BROWNE wrote: This email originated from DIT. If you received this email in error, please delete it from your system. Please note that if you are not the named addressee, disclosing, copying, distributing or taking any action based on the contents of this email or attachments is prohibited. www.dit.ie Is ó ITBÁC a tháinig an ríomhphost seo. Má fuair tú an ríomhphost seo trí earráid, scrios de do chóras é le do thoil. Tabhair ar aird, mura tú an seolaí ainmnithe, go bhfuil dianchosc ar aon nochtadh, aon chóipeáil, aon dáileadh nó ar aon ghníomh a dhéanfar bunaithe ar an ábhar atá sa ríomhphost nó sna hiatáin seo. www.dit.ie Tá ITBÁC ag aistriú go Gráinseach Ghormáin – DIT is on the move to Grangegorman _______________________________________________ Beginners mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners |
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