<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">I get:<div class=""><br class=""><div class=""><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">Doaitse-2:~ doaitse$ ghci</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">GHCi, version 8.4.3: <a href="http://www.haskell.org/ghc/" class="">http://www.haskell.org/ghc/</a> :? for help</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">Prelude> :set -XGADTs</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">Prelude> data Q = forall a.Q a</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255); min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><b class=""><interactive>:2:10: </b></span><span style="font-variant-ligatures: no-common-ligatures; color: #c33720" class=""><b class="">error:</b></span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><b class=""> Not a data constructor: ‘forall’</b></span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><b class=""> Perhaps you intended to use ExistentialQuantification</b></span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">Prelude> </span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class="">It is weird that the forall (which actually is an exists) was enabled by the -XExplicitForAll</span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> Doaitse</span></div><div class=""><br class=""><blockquote type="cite" class=""><div class="">Op 27 aug. 2018, om 3:42 heeft Cosmia Fu <<a href="mailto:cosmiafu@gmail.com" class="">cosmiafu@gmail.com</a>> het volgende geschreven:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Hey everyone,<br class=""><br class="">I found that it seems that GADTs implies ExistentialQuantification, but not mentioned in the manual. Is it a bug?<br class=""><a href="https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html#extension-GADTs" class="">https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html#extension-GADTs</a><br class=""><br class="">GHCi, version 8.4.3: <a href="http://www.haskell.org/ghc/" class="">http://www.haskell.org/ghc/</a> :? for help<br class="">Prelude> :set -XGADTs -XExplicitForAll<br class="">Prelude> data Q = forall a. Q a<br class="">Prelude><br class=""><br class="">----<br class=""><br class="">Cosmia Fu</div>
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