<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Jun 17, 2018, at 10:01 AM, sasa bogicevic <<a href="mailto:brutallesale@gmail.com" class="">brutallesale@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">So I guess that we need to check if one of the kinds of two types we are comparing defaults to * (or Type if you will) and then</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">add new warning that will be more descriptive as to why the failure happened. Maybe there is a way to check if what we are</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">comparing are actually type families so that would make the job easier I guess.</div></div></blockquote><div><br class=""></div><div>I don't think the problem is particular to `Type` or defaulting. Instead, the problem is when one of the two mismatched types is a type family application where the type family has equations that pattern-match on an invisible parameter, and it's that invisible-parameter matching that's gone awry. Now that I think about it, detecting these particular conditions might be tricky: you might need to edit code in FamInstEnv that does type family equation lookup to return diagnostic information if a match fails. (I would look at reduceTyFamApp_maybe, and perhaps it can return something more interesting than Nothing in the failure case.) </div><br class=""><blockquote type="cite" class=""><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Richard Eisenberg offered some help on this but I am not sure how to grab hold of him so I'd appreciate any help I could get.</div><br class="Apple-interchange-newline"></div></blockquote></div><br class=""><div class="">Just email! :)</div><div class=""><br class=""></div><div class="">Thanks for looking into this!</div><div class="">Richard</div></body></html>