@Alex,<div><div><br></div><div>OK that starts to make sense. Many thanks. Can we say that a data constructor is a way of expression polymorphic types? I don't know if that even makes sense in the Haskell context?</div><div><br></div><div>Thanks</div><br><signature>Sent from <a href="https://n1.nylas.com/link/496a95782b700a0d942b7edbb78d7d49a0d9287887a79f6ddc867889ceee2b88/0?redirect=https%3A%2F%2Fnylas.com%3Fref%3Dn1">Nylas Mail</a>, the best free email app for work</signature>
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            On Sep 14 2017, at 6:56 am, Alex Belanger &lt;i.caught.air@gmail.com&gt; wrote:
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            <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
              <div dir="auto">I'm on my phone which makes replying painful, but consider:<div dir="auto"><br></div><div dir="auto">data Weekday = Monday | Tuesday | Wednesday | Thursday | Friday</div><div dir="auto"><br></div><div dir="auto">data Shape = Circle Int | Rectangle Int Int Int Int | Triangle Int Int</div><div dir="auto"><br></div><div dir="auto">data Either a b = Left a | Right b</div><div dir="auto"><br></div><div dir="auto">Cheers,</div><div dir="auto">Alex</div></div><div><div><br></div><div>On Sep 14, 2017 12:05 AM, "Anwar Ludin" &lt;<a href="mailto:anwar.ludin@gmail.com">anwar.ludin@gmail.com</a>&gt; wrote:<br type="attribution"><blockquote style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hello everyone,<div><br></div><div>I have just started studying Haskell and I am having a hard time understanding type and value constructors.</div><div><br></div><div>So to create a new type, you write something like:</div><div><br></div><div>data FinancialInstrument = Financial &nbsp;String Double</div><div>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;deriving (Eq, Show)</div><div><br></div><div>and then you can write:</div><div><br></div><div>ibm = Financial "ibm" 150</div><div><br></div><div>OK all good. This initializes a FinancialInstrument. What I don't quite grasp is what is the purpose of Financial (the data/value constructor)? And from what I have read, you could have also written:</div><div><br></div><div>data FinancialInstrument = FinancialInstrument String Double</div><div>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;deriving (Eq, Show)</div><div><br></div><div>To me the second expression is a lot closer to the typical OOP way of doing things (where the type name and constructor(s) have the same name). Why would someone prefer the first notation?</div><div><br></div><div>Once a value has been constructed, how can I access its fields?</div><div><br></div><div>Is there a way to create values using named parameters?</div><div><br></div><div>Thanks!&nbsp;</div></div>
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