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June 2016

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2 discussions

(issue tracker,) deriving multiple instances
by lennart spitzner 28 Jun '16

28 Jun '16

hi, firstly, the "official" syb issue tracker is read-only. My real question is if the code below is not supposed to work, or if there exists a way to make it work. The direct cause of the error is obvious, and I can think of an (ugly) workaround (define different instances in separate modules), but I'd like to know if such usage of Data is considered bad for some reason. code, error and derived instance: > {-# LANGUAGE StandaloneDeriving #-} > {-# LANGUAGE DeriveDataTypeable #-} > {-# LANGUAGE FlexibleInstances #-} > > import Data.Data ( Data ) > > data Foo f = Foo (f Bool) (f Int) > > deriving instance Data (Foo []) > deriving instance Data (Foo Maybe) ghc-7.10.3 error (ghc-8.0.1 shows the same general behaviour, though the internal identifiers are longer): > Main.hs: line 45, column 1: > Multiple declarations of ‘$cr2C’ > Declared at: Main.hs:44:1 > Main.hs:45:1 > Main.hs: line 45, column 1: > Multiple declarations of ‘$tr2D’ > Declared at: Main.hs:44:1 > Main.hs:45:1 > Main.hs: line 45, column 1: > Duplicate type signatures for ‘$tr2D’ > at Main.hs:44:1-31 > Main.hs:45:1-34 > Main.hs: line 45, column 1: > Duplicate type signatures for ‘$cr2C’ > at Main.hs:44:1-31 > Main.hs:45:1-34 ghc -ddump-deriv for a single instance: > Derived instances: > instance Data.Data.Data (Main.Foo []) where > Data.Data.gfoldl k_a45I z_a45J (Main.Foo a1_a45K a2_a45L) > = ((z_a45J Main.Foo `k_a45I` a1_a45K) `k_a45I` a2_a45L) > Data.Data.gunfold k_a45M z_a45N _ > = k_a45M (k_a45M (z_a45N Main.Foo)) > Data.Data.toConstr (Main.Foo _ _) = Main.$cr3ji > Data.Data.dataTypeOf _ = Main.$tr3gf > > Main.$tr3gf :: Data.Data.DataType > Main.$cr3ji :: Data.Data.Constr > Main.$tr3gf = Data.Data.mkDataType "Foo" [Main.$cr3ji] > Main.$cr3ji > = Data.Data.mkConstr Main.$tr3gf "Foo" [] Data.Data.Prefix

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Summer School on Bidirectional Transformations, Oxford, 25-29th July 2016
by Jeremy Gibbons 02 Jun '16

02 Jun '16

Apologies if you have seen this before, but the early registration deadline (June 10th) is fast approaching for SSBX in Oxford. Please pass this on to anyone who may be interested (and consider coming yourself!). * SUMMER SCHOOL ON BIDIRECTIONAL TRANSFORMATIONS Lady Margaret Hall, Oxford, UK 25th to 29th July 2016 http://www.cs.ox.ac.uk/projects/tlcbx/ssbx/ TOPIC Bidirectional transformations (BX) are means of maintaining consistency between multiple information sources: when one source is edited, the others may need updating to restore consistency. BX have applications in databases, user interface design, model-driven development, and many other domains. This summer school is one of the closing activities on the "Theory of Least Change for BX" project at Oxford and Edinburgh (http://www.cs.ox.ac.uk/projects/tlcbx/) It brings together leading researchers in BX, spanning theory and practice, for a week of lectures in beautiful Oxford. It will be aimed at doctoral students in computer science, but will also be suitable for strong master's students and for researchers. LECTURERS Anthony Anjorin, University of Paderborn, DE "Bx with Triple Graph Grammars" Martin Hofmann, Ludwig-Maximilians-Universitaet Muenchen, DE "Modular Edit Lenses" Zhenjiang Hu, National Institute of Informatics, JP "Principles and Practice of Putback-based Bidirectional Programming in BiGUL" Mike Johnson, Macquarie University, AU "Mathematical Foundations of Bidirectional Transformations" Richard Paige, University of York, UK "Engineering Bidirectional Transformations" The TLCBX team, Universities of Edinburgh and Oxford, UK will introduce, say a bit about TLCBX results, and conclude VENUE The school will take place at Lady Margaret Hall (http://www.lmh.ox.ac.uk/) in leafy North Oxford, right next to the University Parks and the River Cherwell and a short walk from the City Centre. LMH is one of the constituent colleges of the University of Oxford; it was founded in 1878 as the first women's college in Oxford. Our lectures will take place in the splendid Simpkins Lee Theatre in the Pipe Partridge Building, completed in 2010. REGISTRATION The Summer School is financially partially supported by EPSRC. There is an early registration fee of £200 (or £150 for students) if booked before the early registration deadline of 10th June, rising to £250 (or £200 for students) after that point. The registration fee includes lunches, coffee breaks, and a banquet one evening. We have reserved bed-and-breakfast accommodation in college, at £62.50 per night in an ensuite room; there are also a few standard rooms available at £58 per night, but please contact Karen.Barnes(a)cs.ox.ac.uk in advance if you would like to reserve one of them. Those rooms will be released after the early registration deadline, after which point there will be no guarantee of accommodation. Space is limited; there is room for 40 students. FURTHER INFORMATION More information, including the registration link, is on the summer school webpage: http://www.cs.ox.ac.uk/projects/tlcbx/ssbx/ For questions about registration or administrative matters, please contact Karen.Barnes(a)cs.ox.ac.uk. For questions about academic matters, please contact any of the organizers: Faris Abou-Saleh, James Cheney, Jeremy Gibbons, James McKinna, Perdita Stevens * Jeremy.Gibbons(a)cs.ox.ac.uk Oxford University Department of Computer Science, Wolfson Building, Parks Road, Oxford OX1 3QD, UK. +44 1865 283521 http://www.cs.ox.ac.uk/people/jeremy.gibbons/

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