<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Dec 10, 2014, at 12:31 PM, Gautier DI FOLCO <<a href="mailto:gautier.difolco@gmail.com">gautier.difolco@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">2014-12-10 16:21 GMT+01:00 Richard Eisenberg <span dir="ltr"><<a href="mailto:eir@cis.upenn.edu" target="_blank">eir@cis.upenn.edu</a>></span>:<br><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex; position: static; z-index: auto; ">The problem I see here is that your List1 and List2 kinds are essentially untyped. These lists are allowed to store any types. For example, I can say `Cons1 'True (Cons1 Int Nil1)`, even though 'True and Int have different kinds. Your List3 won't allow such a construction. You're right that the kinds aren't isomorphic.<br>
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Does this help?<br></blockquote><div><br>Yes, it does.<br>I guess that there is no way to escape ? <br></div></div></div></div>
</blockquote></div><br><div>Escape what, exactly? I'm not sure what your end goal is, so I don't know what you're trying to escape from.</div><div><br></div><div>Is this what you want?</div><div><br></div><div><div></div></div><blockquote type="cite"><div><div>data List where</div><div> Nil :: List</div><div> Cons :: a -> b -> List</div><div><br></div><div>type Foo = Cons True (Cons "x" (Cons () Nil))</div></div></blockquote><div><br></div><div>That works, but isn't very useful in practice, I don't think...</div><div><br></div><div>Richard</div></body></html>