35 lines
1.2 KiB
Haskell
35 lines
1.2 KiB
Haskell
{-# LANGUAGE NamedFieldPuns #-}
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module Transducer (
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Transducer
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, fromList
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, run
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) where
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import Stream (Stream(..), merge)
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import qualified Stream (empty)
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import Graph (Graph(..), Vertex(..), Zipper(..), editLabel, follow, open, rewind, singleton, weave)
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type Transducer input output = Graph input [output]
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empty :: Transducer input output
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empty = open $ singleton []
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add :: Ord input => Transducer input output -> ([input], output) -> Transducer input output
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add transducer (path, output) =
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rewind $ editLabel (weave transducer path) (output:)
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fromList :: Ord input => [([input], output)] -> Transducer input output
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fromList = foldl add empty
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run :: (Ord input, Eq output) => Transducer input output -> Stream input -> Stream output
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run transducer (Stream inputs) = foldl (\(Stream outputs) (input, stream) ->
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case follow transducer input of
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Nothing -> case context transducer of
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Top -> run (rewind transducer) stream
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_ -> Stream.empty
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Just newState@(Graph {focus}) ->
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Stream ((emit stream <$> label focus) ++ outputs) `merge` run newState stream
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) Stream.empty inputs
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where
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emit stream output = (output, run (rewind transducer) stream)
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