Create 'dequeue in Haskell' (hacktoberfest17#1659)

* Create 'dequeue in Haskell'

* Add a contributor

Author: aiya000

CONTRIBUTORS.md

@@ -1065,4 +1065,4 @@ Programming contributors (sorted contributions)
 
 * **[kserno](https://github.com/kserno)**
 
-
+* **[aiya000](https://github.com/aiya000)**

dequeue/.gitignore

@@ -0,0 +1 @@
+.stack-work

dequeue/Setup.hs

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+import Distribution.Simple
+main = defaultMain

dequeue/dequeue.cabal

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+name:                dequeue
+version:             0.1.0.0
+category:            Hacktoberfest17
+build-type:          Simple
+cabal-version:       >=1.10
+
+executable dequeue
+  hs-source-dirs:      .
+  main-is:             dequeue.hs
+  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
+  build-depends:       base
+                     , containers
+                     , lens
+                     , mtl
+  default-language:    Haskell2010

dequeue/dequeue.hs

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+import Control.Lens hiding ((<|), (|>), (:<), (:>))
+import Control.Monad (void)
+import Control.Monad.IO.Class (liftIO)
+import Control.Monad.State.Lazy (StateT(..), runStateT, get, gets)
+import Data.Sequence
+
+-- 'Seq' is a dequeue
+type Dequeue a = Seq a
+
+main :: IO ()
+main = do
+  putStrLn "-- pure operations"
+  let xs  = fromList [10]
+      xs' = 20 <| xs -- push front
+      xs'' = xs' |> 30 -- push back
+  mapM_ print [xs, xs', xs'']
+  --NOTE: these are unsafe operations (Please see 'context' for safe operations)
+  let (x' :< xs') = viewl xs''
+      (xs :> x) = viewr xs'
+  mapM_ print [x', x]
+  void $ runStateT context xs
+
+context :: StateT (Dequeue Int) IO ()
+context = do
+  liftIO $ putStrLn "-- inpure operations"
+  printState
+  simple %= (20 <|)
+  printState
+  simple %= (|> 30)
+  printState
+  --NOTE: these are safe operations by 'Prism'
+  maybeHead <- gets $ preview _head
+  liftIO $ print maybeHead
+  maybeLast <- gets $ preview _last
+  liftIO $ print maybeLast
+  where
+    printState :: Show s => StateT s IO ()
+    printState = get >>= liftIO . print

dequeue/stack.yaml

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+# This file was automatically generated by 'stack init'
+#
+# Some commonly used options have been documented as comments in this file.
+# For advanced use and comprehensive documentation of the format, please see:
+# https://docs.haskellstack.org/en/stable/yaml_configuration/
+
+# Resolver to choose a 'specific' stackage snapshot or a compiler version.
+# A snapshot resolver dictates the compiler version and the set of packages
+# to be used for project dependencies. For example:
+#
+# resolver: lts-3.5
+# resolver: nightly-2015-09-21
+# resolver: ghc-7.10.2
+# resolver: ghcjs-0.1.0_ghc-7.10.2
+# resolver:
+#  name: custom-snapshot
+#  location: "./custom-snapshot.yaml"
+resolver: lts-9.10
+
+# User packages to be built.
+# Various formats can be used as shown in the example below.
+#
+# packages:
+# - some-directory
+# - https://example.com/foo/bar/baz-0.0.2.tar.gz
+# - location:
+#    git: https://github.com/commercialhaskell/stack.git
+#    commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+# - location: https://github.com/commercialhaskell/stack/commit/e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+#   extra-dep: true
+#  subdirs:
+#  - auto-update
+#  - wai
+#
+# A package marked 'extra-dep: true' will only be built if demanded by a
+# non-dependency (i.e. a user package), and its test suites and benchmarks
+# will not be run. This is useful for tweaking upstream packages.
+packages:
+- .
+# Dependency packages to be pulled from upstream that are not in the resolver
+# (e.g., acme-missiles-0.3)
+# extra-deps: []
+
+# Override default flag values for local packages and extra-deps
+# flags: {}
+
+# Extra package databases containing global packages
+# extra-package-dbs: []
+
+# Control whether we use the GHC we find on the path
+# system-ghc: true
+#
+# Require a specific version of stack, using version ranges
+# require-stack-version: -any # Default
+# require-stack-version: ">=1.5"
+#
+# Override the architecture used by stack, especially useful on Windows
+# arch: i386
+# arch: x86_64
+#
+# Extra directories used by stack for building
+# extra-include-dirs: [/path/to/dir]
+# extra-lib-dirs: [/path/to/dir]
+#
+# Allow a newer minor version of GHC than the snapshot specifies
+# compiler-check: newer-minor