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<p class=MsoNormal><span lang=EN-US>Hey there,<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>i was just thinking about types in Haskell
and I asked myself,<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Is there a mechanism, that allows me to
define a new type out of an existing one with some restrictions?<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>So that the new type is a subset of the existing
one.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Lets imagine I want a type for a point
like:<o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:35.4pt'><span lang=EN-US>type Point =
(Int, Int) <o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>But what, if I can predict that the X and Y
values are in a range between 0 and 100? <o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>If someone defines a new point like:<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>
p :: Point<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>
p = (200, 400) <o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US>that is totally fine with the type definition
above, but not correct in my context. <o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Is it possible, to put this information
into the type? So that the compiler is able to recognize my mistake? <o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>-- Matthias<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><o:p> </o:p></p>
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