[Haskell-beginners] [Haskell-cafe] Comparison between fields of each record

[MJ Williams]

Okay, can I ask you to provide a little more explanation of what you
want to perform with your code? To me, at least, the question, "How
can I fit it?" is a little too terse.

I think before you even set up a new data, class, class instances
etc., the most key step is to put in words, the simpler and cleaer the
better, exactly what you what the code to do for you. Pseudo code in
prose, if you like. You'll find that with clarity of thought expressed
in words comes a greater command of the programming language, or at
least, a clearer idea of what you want from the programming language.

Matthew


On 24/11/2015, Jeon-Young Kang <jykang22 at gmail.com> wrote:
> Thank you so much :)
>
> On Tue, Nov 24, 2015 at 2:01 PM, Francesco Ariis <fa-ml at ariis.it> wrote:
>
>> On Tue, Nov 24, 2015 at 01:20:03PM -0500, Jeon-Young Kang wrote:
>> > Dear All.
>> >
>> > I'd like to compare fields of each record.
>> >
>> > here is my record.
>> >
>> > data Person = Person {name:: String, age:: Int } deriving(Show)
>> > data Relations = Friend | Older | Younger
>> >
>> > class Comparison a where
>> >     compare:: a -> a -> Relations
>> >
>> > instance Comparison Person where
>> >     compare Person a b Person a b
>> >          | b1 == b2 = Friend
>> >          | b1 > b2 = Older
>> >          | b1 < b2 = Younger
>> >
>> > How can I fit it?
>> >
>> > Sincerely,
>> >
>> >
>> > Jeon-Young Kang
>>
>> Hello Jeon-Young, I attach a version that compiles. Keep in mind that
>>
>>     compare (Person x y) (Person q w) -- this is legal
>>
>>     compare Person x y Person q w -- "space" takes precedence over
>> everything,
>>                                   -- so this function has 6 arguments
>>                                   -- instead of the expected 2!
>>
>>
>> λ> Main.compare (Person "cdsac" 1) (Person "cdscasd" 20)
>> Younger
>>
>
>
>
> --
> Department of Geography
> State University of New York at Buffalo
>
> jykang22 at gmail.com
>
> Jeon-Young Kang
>