File ghc-references.spec of Package ghc-references

#
# spec file for package ghc-references
#
# Copyright (c) 2017 SUSE LINUX GmbH, Nuernberg, Germany.
#
# All modifications and additions to the file contributed by third parties
# remain the property of their copyright owners, unless otherwise agreed
# upon. The license for this file, and modifications and additions to the
# file, is the same license as for the pristine package itself (unless the
# license for the pristine package is not an Open Source License, in which
# case the license is the MIT License). An "Open Source License" is a
# license that conforms to the Open Source Definition (Version 1.9)
# published by the Open Source Initiative.

# Please submit bugfixes or comments via http://bugs.opensuse.org/
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%global pkg_name references
%bcond_with tests
Name:           ghc-%{pkg_name}
Version:        0.3.2.1
Release:        0
Summary:        Selectors for reading and updating data
License:        BSD-3-Clause
Group:          Development/Languages/Other
Url:            https://hackage.haskell.org/package/%{pkg_name}
Source0:        https://hackage.haskell.org/package/%{pkg_name}-%{version}/%{pkg_name}-%{version}.tar.gz
BuildRequires:  ghc-Cabal-devel
BuildRequires:  ghc-array-devel
BuildRequires:  ghc-containers-devel
BuildRequires:  ghc-directory-devel
BuildRequires:  ghc-either-devel
BuildRequires:  ghc-filepath-devel
BuildRequires:  ghc-instance-control-devel
BuildRequires:  ghc-mtl-devel
BuildRequires:  ghc-rpm-macros
BuildRequires:  ghc-template-haskell-devel
BuildRequires:  ghc-text-devel
BuildRequires:  ghc-transformers-devel
BuildRequires:  ghc-uniplate-devel
BuildRoot:      %{_tmppath}/%{name}-%{version}-build
%if %{with tests}
BuildRequires:  ghc-HUnit-devel
BuildRequires:  ghc-lens-devel
%endif

%description
References are data accessors that can read, write or update the accessed
infromation through their context. They are first-class values, can be passed
in functions, transformed, combined. References generalize lenses, folds and
traversals for haskell (see: < https://hackage.haskell.org/package/lens>).

References are more general than field selectors in traditional languages.

* References are first-class values. If there is a struct in C, for example,
with an `int` field `fl`, then fl can only be used as part of an expression.
One can not generalize a function to take a field selector and transform the
selected data or use it in other ways.

* They can have different meanings, while field accessors can only represent
data-level containment. They can express uncertain containment (like field
selectors of C unions), different viewpoints of the same data, and other
concepts.

There are two things that references can do but the previously mentioned access
methods don't.

* References can cooperate with monads, for example IO. This opens many new
applications.

* References can be added using the '&+&' operator, to create new lenses more
easily.

Basic idea taken from the currently not maintained package
<https://hackage.haskell.org/package/yall>.

An example use of the references (a logger application that spawns new threads
to update a global log):

> logger = > (forever $ do > log <- logChan ^? chan&logRecord -- Extract the
log record from the received log message > thrId <- forkIO (do time <- getTime
> ioref&lastLogTime != time $ logDB -- Update the last logging time mutable log
database > let logMsg = senderThread .- show -- Transform the thread id to a
string and > $ loggingTime .= time -- update the time > $ log -- inside the log
message > ioref&debugInfos !~ addLogEntry log $ logDB -- update the table of
log entries > mvar !- (+1) $ count ) > mvar !- (thrId:) $ updaters -- Record
the spawned thread > ) `catch` stopUpdaters updaters > where stopUpdaters
updaters ThreadKilled = > mvar&traverse !| killThread $ updaters -- Kill all
spawned threads before stopping

There are a bunch of predefined references for datatypes included in standard
libraries.

New references can be created in several ways:

* From getter, setter and updater, using the 'reference' function.

* From getter and setter, using one of the simplified functions ('lens',
'simplePartial', 'partial', ...).

* Using the `Data.Traversal` instance on a datatype to generate a traversal of
each element.

* Using lenses from `Control.Lens` package. There are a lot of packages
defining lenses, folds and traversals for various data structures, so it is
very useful that all of them can simply be converted into a reference.

* Generating references for newly defined datatypes using the `makeReferences`
Template Haskell function. .

%package devel
Summary:        Haskell %{pkg_name} library development files
Group:          Development/Libraries/Other
Requires:       %{name} = %{version}-%{release}
Requires:       ghc-compiler = %{ghc_version}
Requires(post): ghc-compiler = %{ghc_version}
Requires(postun): ghc-compiler = %{ghc_version}

%description devel
This package provides the Haskell %{pkg_name} library development files.

%prep
%setup -q -n %{pkg_name}-%{version}

%build
%ghc_lib_build

%install
%ghc_lib_install

%check
%cabal_test

%post devel
%ghc_pkg_recache

%postun devel
%ghc_pkg_recache

%files -f %{name}.files
%defattr(-,root,root,-)
%doc LICENSE

%files devel -f %{name}-devel.files
%defattr(-,root,root,-)
%doc CHANGELOG.md README.md

%changelog