From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104]) by sympa.inria.fr (Postfix) with ESMTPS id B05D17EF10 for ; Wed, 25 Feb 2015 05:47:06 +0100 (CET) Received-SPF: None (mail3-smtp-sop.national.inria.fr: no sender authenticity information available from domain of martindemello@gmail.com) identity=pra; client-ip=209.85.213.175; receiver=mail3-smtp-sop.national.inria.fr; envelope-from="martindemello@gmail.com"; x-sender="martindemello@gmail.com"; x-conformance=sidf_compatible Received-SPF: Pass (mail3-smtp-sop.national.inria.fr: domain of martindemello@gmail.com designates 209.85.213.175 as permitted sender) identity=mailfrom; client-ip=209.85.213.175; receiver=mail3-smtp-sop.national.inria.fr; envelope-from="martindemello@gmail.com"; x-sender="martindemello@gmail.com"; x-conformance=sidf_compatible; x-record-type="v=spf1" Received-SPF: None (mail3-smtp-sop.national.inria.fr: no sender authenticity information available from domain of postmaster@mail-ig0-f175.google.com) identity=helo; client-ip=209.85.213.175; receiver=mail3-smtp-sop.national.inria.fr; envelope-from="martindemello@gmail.com"; x-sender="postmaster@mail-ig0-f175.google.com"; x-conformance=sidf_compatible X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: A0BoAQDsUu1Um6/VVdFbg1daBIMEwCKFJYFsB0MBAQEBAQEQAQEBAQEGCwsJFC6EKBEdARseAxIQDwImAiQBEQEFASI1h3gBAxENq1WDKz4xiy6Ba4J3jjgKGScNVIRdJgEBBA6BE5FPgUMFik6IbYVlgRuDGY09EiOBDAmEMR0xgkMBAQE X-IPAS-Result: A0BoAQDsUu1Um6/VVdFbg1daBIMEwCKFJYFsB0MBAQEBAQEQAQEBAQEGCwsJFC6EKBEdARseAxIQDwImAiQBEQEFASI1h3gBAxENq1WDKz4xiy6Ba4J3jjgKGScNVIRdJgEBBA6BE5FPgUMFik6IbYVlgRuDGY09EiOBDAmEMR0xgkMBAQE X-IronPort-AV: E=Sophos;i="5.09,643,1418079600"; d="scan'208";a="101220760" Received: from mail-ig0-f175.google.com ([209.85.213.175]) by mail3-smtp-sop.national.inria.fr with ESMTP/TLS/RC4-SHA; 25 Feb 2015 05:47:05 +0100 Received: by mail-ig0-f175.google.com with SMTP id hn18so32666570igb.2 for ; Tue, 24 Feb 2015 20:47:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:date:message-id:subject:from:to:content-type; bh=lPVeGkUjm2eJ+tAoZjCvOsyoYwKer/J1O8A3J8SFAnI=; b=KbZ5p4mCxVMXDBmXSzMVrB3KDGYRq3zK8dESpbJ76hr18ryT8wym4/1Cz+vpRPQBgl DQ+NTR3b7z0xIfeiIb9JS5dMeBbKj8R5UOPrXtNrMFO0NzLdYJS4QvTi6k87PkSdYwkt 8nxqsJo0Da/JffNEzLvwnn4LCzx9b4U426BurkpJ4/pUTlmN0IItKJDTnH5aaC/bHBD4 kgXTe+sbM8IRGWwealV1PTrdyQfeH0aBlakBEvnPC9B5KUNdETw7Z9zG/dkwjgAC/mwF CYoIuWpDZQRKnmj35Nyf1nkTK7Y0t82TrY5TS8KMaGFYHeLLQz2sBRRXs6DEcuBLNtXH 8vBw== MIME-Version: 1.0 X-Received: by 10.42.138.199 with SMTP id d7mr1850018icu.3.1424839624142; Tue, 24 Feb 2015 20:47:04 -0800 (PST) Received: by 10.107.152.213 with HTTP; Tue, 24 Feb 2015 20:47:04 -0800 (PST) Date: Tue, 24 Feb 2015 20:47:04 -0800 Message-ID: From: Martin DeMello To: OCaml List Content-Type: text/plain; charset=UTF-8 Subject: [Caml-list] "this ground coercion is not principal" What does this warning mean? I got it while compiling some code off github [https://github.com/JoeDralliam/OcsfmlExamples/blob/master/Examples/sockets.ml] and by experimenting it seems to be related to this bit from the manual Note that the coercion ( expr :> typexpr ) is actually an abbreviated form, and will only work in presence of private abbreviations if neither the type of expr nor typexpr contain any type variables. If they do, you must use the full form ( expr : typexpr1 :> typexpr2 ) where typexpr1 is the expected type of expr. Concretely, this would be (x : N.t :> int) and (l : N.t list :> int list) for the above examples. but I could not find anything on google for either "ground coercion" or "principal type coercion" that would explain what it was actually saying. Could someone please point me to a reference? martin