Starting with simple streams

CHANGELOG.md

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+# Revision history for Mainate
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.

LICENSE

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+Copyright (c) 2019, Tissevert
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Tissevert nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Mainate.cabal

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+cabal-version:       >=1.10
+-- Initial package description 'Mainate.cabal' generated by 'cabal init'.
+-- For further documentation, see http://haskell.org/cabal/users-guide/
+
+name:                Mainate
+version:             0.1.0.0
+synopsis:            An NLP library to write parsers
+-- description:
+homepage:            https://git.marvid.fr/Tissevert/Mainate.git
+-- bug-reports:
+license:             BSD3
+license-file:        LICENSE
+author:              Tissevert
+maintainer:          tissevert+devel@marvid.fr
+-- copyright:
+category:            Language
+build-type:          Simple
+extra-source-files:  CHANGELOG.md
+
+library
+  exposed-modules:   Stream
+  -- other-modules:
+  -- other-extensions:
+  build-depends:       base >=4.12 && <4.13
+  hs-source-dirs:      src
+  default-language:    Haskell2010

src/Stream.hs

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+module Stream (
+    Stream(..)
+  ) where
+
+import Data.List (intercalate)
+
+data Stream a = Stream [(a, Stream a)] deriving Show
+
+instance Semigroup (Stream a) where
+  (<>) (Stream []) b = b
+  (<>) (Stream pairs) b = Stream $ (\(a, stream) -> (a, stream <> b)) <$> pairs
+
+instance Monoid (Stream a) where
+  mempty = fromList []
+
+fromList :: [a] -> Stream a
+fromList [] = Stream []
+fromList (pair:pairs) = Stream [(pair, fromList pairs)]
+
+infinite :: a -> Stream a
+infinite a = Stream [(a, infinite a)]
+
+showTree :: Show a => Stream a -> String
+showTree = intercalate "\n" . getLines
+  where
+    getLines (Stream []) = ["●"]
+    getLines (Stream pairs) =
+      concat $ (\(a, stream) -> showElem a $ getLines stream) <$> pairs
+
+showElem :: Show a => a -> [String] -> [String]
+showElem _ [] = []
+showElem a [l] = ["— " ++ show a ++ " —" ++ l]
+showElem a (l:ls) =
+  let prefix = "─ " ++ show a ++ " ─┬" in
+  let padding = take (length prefix - 1) $ repeat ' ' in
+  (prefix ++ l) : (pad padding ls)
+  where
+    pad _ [] = []
+    pad padding [x] = [padding ++ '╰' : x]
+    pad padding (x:xs) = (padding ++ '├' : x) : (pad padding xs)