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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Thanks Yury,</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">The problem with this solution is that if I have written a method for the Tensor type (for example a method of a typeclass of which Tensor is an instance) that uses the order of the tensor (your "ndims") in a general way, I cannot reuse it easily for a vector defined like that.</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">In fact, my problem is to be able to define:</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">* from my type "Tensor", a type "Vector", by specifying that the dimension must be one to have a "Vector" type.</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">* from my constructor "TensorVar", a constructor "VectorVar", which corresponds to TensorVar with the integer equal to 1.</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">The idea is to avoid duplicating code, by reusing the tensor type and data constructor. At some place in my code, in some definition (say, of a vector product), I want vectors and not more general tensors.</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">TP</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">On Saturday, April 27, 2013 16:16:49 Yury Sulsky wrote:<br /></p>
<p style=" margin-top:12px; margin-bottom:0px; margin-left:40px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Hi TP,</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:40px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Are you looking to use a phantom types here? Here's an example:</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:40px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">data One</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:40px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">data Two</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:40px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">data Tensor ndims a = Tensor { dims :: [Int], items :: [a] }</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:40px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">type Vector = Tensor One</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:40px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">type Matrix = Tensor Two</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:40px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">etc.</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:40px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">On Sat, Apr 27, 2013 at 3:33 PM, TP <<a href="mailto:paratribulations@free.fr"><span style=" text-decoration: underline; color:#0057ae;">paratribulations@free.fr</span></a>> wrote:<br /></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:45px; margin-right:40px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Hello,<br /><br />I ask myself if there is a way to do the following.<br />Imagine that I have a dummy type:<br /><br />data Tensor = TensorVar Int String<br /><br />where the integer is the order, and the string is the name of the tensor.<br />I would like to make with the constructor TensorVar a type "Vector", such<br />that, in "pseudo-language":<br /><br />data Vector = TensorVar 1 String<br /><br />Because a vector is a tensor of order 1.<br /><br />Is this possible? I have tried type synonyms and newtypes without any success.<br /><br />Thanks a lot,<br /><br />TP<br /></p></body></html>