<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;" class="">I don't think there's an easy way to do this. We could imagine extending Quasi to have a method to check for coercibility, but I don't think there's a way to do this in the current TH API. Sorry!<div class=""><br class=""></div><div class="">Richard</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On May 4, 2018, at 3:44 AM, Travis Whitaker <<a href="mailto:pi.boy.travis@gmail.com" class="">pi.boy.travis@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="gmail_quote"><div dir="ltr" class="">Given that Coercible instances are Deeply Magical, perhaps I'm being a bit naive here, but I recently tried to write a TH function that can check if one type is a newtype of another (or a newtype of a newtype of another, etc).<div class=""><br class=""></div><font face="monospace, monospace" class="">coercibleToFrom :: Type -> Type -> Q Bool<br class="">coercibleToFrom tx ty = (&&) <$> isInstance ''Coercible [tx, ty]<br class=""> <*> isInstance ''Coercible [ty, tx]</font><br class=""><div class=""><font face="monospace, monospace" class=""><br class=""></font></div><div class=""><font face="arial, helvetica, sans-serif" class="">If this worked as I'd hoped, I'm almost certain checking reflexively is redundant. However, I can't seem to get reifyInstances to ever return an InstanceDec for a Coercible instance. Given that these instances are generated on the fly by the typechecker, there's no way to make them available at TH runtime, correct? And, given that, is there an easy way to find out with TH whether not I'll be able to use coerce without taking all the Decs apart to hunt for NewtypeD?</font></div><span class="HOEnZb"><font color="#888888" class=""><div class=""><font face="arial, helvetica, sans-serif" class=""><br class=""></font></div><div class=""><font face="arial, helvetica, sans-serif" class="">Travis</font></div></font></span></div>
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