{-# LANGUAGE RankNTypes, TypeFamilies, BangPatterns, Trustworthy #-}
-module Pipes.Text (
- -- * Effectful Text
- -- $intro
-
- -- * Lenses
- -- $lenses
-
- -- ** @view@ \/ @(^.)@
- -- $view
-
- -- ** @over@ \/ @(%~)@
- -- $over
-
- -- ** @zoom@
- -- $zoom
-
- -- * Special types: @Producer Text m (Producer Text m r)@ and @FreeT (Producer Text m) m r@
- -- $special
+{-| The module @Pipes.Text@ closely follows @Pipes.ByteString@ from
+ the @pipes-bytestring@ package. A draft tutorial can be found in
+ @Pipes.Text.Tutorial@.
+-}
+module Pipes.Text (
-- * Producers
fromLazy
words,
writeFile )
-{- $intro
- This package provides @pipes@ utilities for /text streams/ or /character streams/,
- realized as streams of 'Text' chunks. The individual chunks are uniformly /strict/,
- and thus you will generally want @Data.Text@ in scope. But the type
- @Producer Text m r@ ,as we are using it, is a sort of /pipes/ equivalent of the lazy @Text@ type.
-
- This particular module provides many functions equivalent in one way or another to
- the pure functions in
- <https://hackage.haskell.org/package/text-1.1.0.0/docs/Data-Text-Lazy.html Data.Text.Lazy>.
- They transform, divide, group and fold text streams. Though @Producer Text m r@
- is the type of \'effectful Text\', the functions in this module are \'pure\'
- in the sense that they are uniformly monad-independent.
- Simple /IO/ operations are defined in @Pipes.Text.IO@ -- as lazy IO @Text@
- operations are in @Data.Text.Lazy.IO@. Inter-operation with @ByteString@
- is provided in @Pipes.Text.Encoding@, which parallels @Data.Text.Lazy.Encoding@.
-
- The Text type exported by @Data.Text.Lazy@ is basically that of a lazy list of
- strict Text: the implementation is arranged so that the individual strict 'Text'
- chunks are kept to a reasonable size; the user is not aware of the divisions
- between the connected 'Text' chunks.
- So also here: the functions in this module are designed to operate on streams that
- are insensitive to text boundaries. This means that they may freely split
- text into smaller texts and /discard empty texts/. The objective, though, is
- that they should /never concatenate texts/ in order to provide strict upper
- bounds on memory usage.
-
- For example, to stream only the first three lines of 'stdin' to 'stdout' you
- might write:
-
-> import Pipes
-> import qualified Pipes.Text as Text
-> import qualified Pipes.Text.IO as Text
-> import Pipes.Group (takes')
-> import Lens.Family
->
-> main = runEffect $ takeLines 3 Text.stdin >-> Text.stdout
-> where
-> takeLines n = Text.unlines . takes' n . view Text.lines
-
- The above program will never bring more than one chunk of text (~ 32 KB) into
- memory, no matter how long the lines are.
-
--}
-{- $lenses
- As this example shows, one superficial difference from @Data.Text.Lazy@
- is that many of the operations, like 'lines', are \'lensified\'; this has a
- number of advantages (where it is possible); in particular it facilitates their
- use with 'Parser's of Text (in the general <http://hackage.haskell.org/package/pipes-parse-3.0.1/docs/Pipes-Parse-Tutorial.html pipes-parse>
- sense.) The disadvantage, famously, is that the messages you get for type errors can be
- a little alarming. The remarks that follow in this section are for non-lens adepts.
-
- Each lens exported here, e.g. 'lines', 'chunksOf' or 'splitAt', reduces to the
- intuitively corresponding function when used with @view@ or @(^.)@. Instead of
- writing:
-
- > splitAt 17 producer
-
- as we would with the Prelude or Text functions, we write
-
- > view (splitAt 17) producer
-
- or equivalently
-
- > producer ^. splitAt 17
-
- This may seem a little indirect, but note that many equivalents of
- @Text -> Text@ functions are exported here as 'Pipe's. Here too we recover the intuitively
- corresponding functions by prefixing them with @(>->)@. Thus something like
-
-> stripLines = Text.unlines . Group.maps (>-> Text.stripStart) . view Text.lines
-
- would drop the leading white space from each line.
-
- The lenses in this library are marked as /improper/; this just means that
- they don't admit all the operations of an ideal lens, but only /getting/ and /focusing/.
- Just for this reason, though, the magnificent complexities of the lens libraries
- are a distraction. The lens combinators to keep in mind, the ones that make sense for
- our lenses, are @view@ \/ @(^.)@), @over@ \/ @(%~)@ , and @zoom@.
-
- One need only keep in mind that if @l@ is a @Lens' a b@, then:
-
--}
-{- $view
- @view l@ is a function @a -> b@ . Thus @view l a@ (also written @a ^. l@ )
- is the corresponding @b@; as was said above, this function will be exactly the
- function you think it is, given its name. Thus to uppercase the first n characters
- of a Producer, leaving the rest the same, we could write:
-
-
- > upper n p = do p' <- p ^. Text.splitAt n >-> Text.toUpper
- > p'
--}
-{- $over
- @over l@ is a function @(b -> b) -> a -> a@. Thus, given a function that modifies
- @b@s, the lens lets us modify an @a@ by applying @f :: b -> b@ to
- the @b@ that we can \"see\" through the lens. So @over l f :: a -> a@
- (it can also be written @l %~ f@).
- For any particular @a@, then, @over l f a@ or @(l %~ f) a@ is a revised @a@.
- So above we might have written things like these:
-
- > stripLines = Text.lines %~ maps (>-> Text.stripStart)
- > stripLines = over Text.lines (maps (>-> Text.stripStart))
- > upper n = Text.splitAt n %~ (>-> Text.toUpper)
-
--}
-{- $zoom
- @zoom l@, finally, is a function from a @Parser b m r@
- to a @Parser a m r@ (or more generally a @StateT (Producer b m x) m r@).
- Its use is easiest to see with an decoding lens like 'utf8', which
- \"sees\" a Text producer hidden inside a ByteString producer:
- @drawChar@ is a Text parser, returning a @Maybe Char@, @zoom utf8 drawChar@ is
- a /ByteString/ parser, returning a @Maybe Char@. @drawAll@ is a Parser that returns
- a list of everything produced from a Producer, leaving only the return value; it would
- usually be unreasonable to use it. But @zoom (splitAt 17) drawAll@
- returns a list of Text chunks containing the first seventeen Chars, and returns the rest of
- the Text Producer for further parsing. Suppose that we want, inexplicably, to
- modify the casing of a Text Producer according to any instruction it might
- contain at the start. Then we might write something like this:
-
-> obey :: Monad m => Producer Text m b -> Producer Text m b
-> obey p = do (ts, p') <- lift $ runStateT (zoom (Text.splitAt 7) drawAll) p
-> let seven = T.concat ts
-> case T.toUpper seven of
-> "TOUPPER" -> p' >-> Text.toUpper
-> "TOLOWER" -> p' >-> Text.toLower
-> _ -> do yield seven
-> p'
-
-
-> >>> let doc = each ["toU","pperTh","is document.\n"]
-> >>> runEffect $ obey doc >-> Text.stdout
-> THIS DOCUMENT.
-
- The purpose of exporting lenses is the mental economy achieved with this three-way
- applicability. That one expression, e.g. @lines@ or @splitAt 17@ can have these
- three uses is no more surprising than that a pipe can act as a function modifying
- the output of a producer, namely by using @>->@ to its left: @producer >-> pipe@
- -- but can /also/ modify the inputs to a consumer by using @>->@ to its right:
- @pipe >-> consumer@
-
- The three functions, @view@ \/ @(^.)@, @over@ \/ @(%~)@ and @zoom@ are supplied by
- both <http://hackage.haskell.org/package/lens lens> and
- <http://hackage.haskell.org/package/lens-family lens-family> The use of 'zoom' is explained
- in <http://hackage.haskell.org/package/pipes-parse-3.0.1/docs/Pipes-Parse-Tutorial.html Pipes.Parse.Tutorial>
- and to some extent in the @Pipes.Text.Encoding@ module here.
-
--}
-{- $special
- These simple 'lines' examples reveal a more important difference from @Data.Text.Lazy@ .
- This is in the types that are most closely associated with our central text type,
- @Producer Text m r@. In @Data.Text@ and @Data.Text.Lazy@ we find functions like
-
-> splitAt :: Int -> Text -> (Text, Text)
-> lines :: Text -> [Text]
-> chunksOf :: Int -> Text -> [Text]
-
- which relate a Text with a pair of Texts or a list of Texts.
- The corresponding functions here (taking account of \'lensification\') are
-
-> view . splitAt :: (Monad m, Integral n) => n -> Producer Text m r -> Producer Text m (Producer Text m r)
-> view lines :: Monad m => Producer Text m r -> FreeT (Producer Text m) m r
-> view . chunksOf :: (Monad m, Integral n) => n -> Producer Text m r -> FreeT (Producer Text m) m r
-
- Some of the types may be more readable if you imagine that we have introduced
- our own type synonyms
-
-> type Text m r = Producer T.Text m r
-> type Texts m r = FreeT (Producer T.Text m) m r
-
- Then we would think of the types above as
-
-> view . splitAt :: (Monad m, Integral n) => n -> Text m r -> Text m (Text m r)
-> view lines :: (Monad m) => Text m r -> Texts m r
-> view . chunksOf :: (Monad m, Integral n) => n -> Text m r -> Texts m r
-
- which brings one closer to the types of the similar functions in @Data.Text.Lazy@
-
- In the type @Producer Text m (Producer Text m r)@ the second
- element of the \'pair\' of effectful Texts cannot simply be retrieved
- with something like 'snd'. This is an \'effectful\' pair, and one must work
- through the effects of the first element to arrive at the second Text stream, even
- if you are proposing to throw the Text in the first element away.
- Note that we use Control.Monad.join to fuse the pair back together, since it specializes to
-
-> join :: Monad m => Producer Text m (Producer m r) -> Producer m r
-
- The return type of 'lines', 'words', 'chunksOf' and the other /splitter/ functions,
- @FreeT (Producer m Text) m r@ -- our @Texts m r@ -- is the type of (effectful)
- lists of (effectful) texts. The type @([Text],r)@ might be seen to gather
- together things of the forms:
-
-> r
-> (Text,r)
-> (Text, (Text, r))
-> (Text, (Text, (Text, r)))
-> (Text, (Text, (Text, (Text, r))))
-> ...
-
- (We might also have identified the sum of those types with @Free ((,) Text) r@
- -- or, more absurdly, @FreeT ((,) Text) Identity r@.)
-
- Similarly, our type @Texts m r@, or @FreeT (Text m) m r@ -- in fact called
- @FreeT (Producer Text m) m r@ here -- encompasses all the members of the sequence:
-
-> m r
-> Text m r
-> Text m (Text m r)
-> Text m (Text m (Text m r))
-> Text m (Text m (Text m (Text m r)))
-> ...
-
- We might have used a more specialized type in place of @FreeT (Producer a m) m r@,
- or indeed of @FreeT (Producer Text m) m r@, but it is clear that the correct
- result type of 'lines' will be isomorphic to @FreeT (Producer Text m) m r@ .
-
- One might think that
-
-> lines :: Monad m => Lens' (Producer Text m r) (FreeT (Producer Text m) m r)
-> view . lines :: Monad m => Producer Text m r -> FreeT (Producer Text m) m r
-
- should really have the type
-
-> lines :: Monad m => Pipe Text Text m r
-
- as e.g. 'toUpper' does. But this would spoil the control we are
- attempting to maintain over the size of chunks. It is in fact just
- as unreasonable to want such a pipe as to want
-
-> Data.Text.Lazy.lines :: Text -> Text
-
- to 'rechunk' the strict Text chunks inside the lazy Text to respect
- line boundaries. In fact we have
-
-> Data.Text.Lazy.lines :: Text -> [Text]
-> Prelude.lines :: String -> [String]
-
- where the elements of the list are themselves lazy Texts or Strings; the use
- of @FreeT (Producer Text m) m r@ is simply the 'effectful' version of this.
-
- The @Pipes.Group@ module, which can generally be imported without qualification,
- provides many functions for working with things of type @FreeT (Producer a m) m r@.
- In particular it conveniently exports the constructors for @FreeT@ and the associated
- @FreeF@ type -- a fancy form of @Either@, namely
-
-> data FreeF f a b = Pure a | Free (f b)
-
- for pattern-matching. Consider the implementation of the 'words' function, or
- of the part of the lens that takes us to the words; it is compact but exhibits many
- of the points under discussion, including explicit handling of the @FreeT@ and @FreeF@
- constuctors. Keep in mind that
-
-> newtype FreeT f m a = FreeT (m (FreeF f a (FreeT f m a)))
-> next :: Monad m => Producer a m r -> m (Either r (a, Producer a m r))
-
- Thus the @do@ block after the @FreeT@ constructor is in the base monad, e.g. 'IO' or 'Identity';
- the later subordinate block, opened by the @Free@ constructor, is in the @Producer@ monad:
-
-> words :: Monad m => Producer Text m r -> FreeT (Producer Text m) m r
-> words p = FreeT $ do -- With 'next' we will inspect p's first chunk, excluding spaces;
-> x <- next (p >-> dropWhile isSpace) -- note that 'dropWhile isSpace' is a pipe, and is thus *applied* with '>->'.
-> return $ case x of -- We use 'return' and so need something of type 'FreeF (Text m) r (Texts m r)'
-> Left r -> Pure r -- 'Left' means we got no Text chunk, but only the return value; so we are done.
-> Right (txt, p') -> Free $ do -- If we get a chunk and the rest of the producer, p', we enter the 'Producer' monad
-> p'' <- view (break isSpace) -- When we apply 'break isSpace', we get a Producer that returns a Producer;
-> (yield txt >> p') -- so here we yield everything up to the next space, and get the rest back.
-> return (words p'') -- We then carry on with the rest, which is likely to begin with space.
-
--}
-- | Convert a lazy 'TL.Text' into a 'Producer' of strict 'Text's
fromLazy :: (Monad m) => TL.Text -> Producer' Text m ()
--- /dev/null
+{-# OPTIONS_GHC -fno-warn-unused-imports #-}
+
+module Pipes.Text.Tutorial (
+ -- * Effectful Text
+ -- $intro
+ -- ** @Pipes.Text@
+ -- $pipestext
+ -- ** @Pipes.Text.IO@
+ -- $pipestextio
+ -- ** @Pipes.Text.Encoding@
+ -- $pipestextencoding
+ -- * Lenses
+ -- $lenses
+
+ -- ** @view@ \/ @(^.)@
+ -- $view
+
+ -- ** @over@ \/ @(%~)@
+ -- $over
+
+ -- ** @zoom@
+ -- $zoom
+
+ -- * Special types: @Producer Text m (Producer Text m r)@ and @FreeT (Producer Text m) m r@
+ -- $special
+ ) where
+
+import Pipes
+import Pipes.Text
+import Pipes.Text.IO
+import Pipes.Text.Encoding
+
+{- $intro
+ This package provides @pipes@ utilities for /character streams/,
+ realized as streams of 'Text' chunks. The individual chunks are uniformly /strict/,
+ and thus the @Text@ type we are using is the one from @Data.Text@, not @Data.Text.Lazy@
+ But the type @Producer Text m r@, as we are using it, is a sort of /pipes/ equivalent of
+ the lazy @Text@ type.
+
+ The main @Pipes.Text@ module provides many functions equivalent
+ in one way or another to the pure functions in
+ <https://hackage.haskell.org/package/text-1.1.0.0/docs/Data-Text-Lazy.html Data.Text.Lazy>
+ (and the corresponding @Prelude@ functions for @String@ s): they transform,
+ divide, group and fold text streams. Though @Producer Text m r@
+ is the type of \'effectful Text\', the functions in @Pipes.Text@ are \'pure\'
+ in the sense that they are uniformly monad-independent.
+ Simple /IO/ operations are defined in @Pipes.Text.IO@ - as lazy IO @Text@
+ operations are in @Data.Text.Lazy.IO@. Similarly, as @Data.Text.Lazy.Encoding@
+ handles inter-operation with @Data.ByteString.Lazy@, @Pipes.Text.Encoding@ provides for
+ interoperation with the \'effectful ByteStrings\' of @Pipes.ByteString@.
+
+ Remember that the @Text@ type exported by @Data.Text.Lazy@ is basically
+ that of a lazy list of strict @Text@: the implementation is arranged so that
+ the individual strict 'Text' chunks are kept to a reasonable size; the user
+ is not aware of the divisions between the connected 'Text' chunks, but uses
+ operations akin to those for strict text.
+ So also here: the functions in this module are designed to operate on character streams that
+ in a way that is independent of the boundaries of the underlying @Text@ chunks.
+ This means that they may freely split text into smaller texts and /discard empty texts/.
+ The objective, though, is that they should not /concatenate texts/ in order to provide strict upper
+ bounds on memory usage.
+
+ For example, to stream only the first three lines of 'stdin' to 'stdout' you
+ might write:
+
+> import Pipes
+> import qualified Pipes.Text as Text
+> import qualified Pipes.Text.IO as Text
+> import Pipes.Group (takes')
+> import Lens.Family (view)
+>
+> main = runEffect $ takeLines 3 Text.stdin >-> Text.stdout
+> where
+> takeLines n = view Text.unlines . takes' n . view Text.lines
+
+ This program will never bring more into memory than what @Text.stdin@ considers
+ one chunk of text (~ 32 KB), even if individual lines are split across many chunks.
+
+-}
+{- $lenses
+ As the use of @view@ in this example shows, one superficial difference from @Data.Text.Lazy@
+ is that many of the operations, like 'lines', are \'lensified\'; this has a
+ number of advantages; in particular it facilitates their use with 'Parser's of Text
+ (in the general <http://hackage.haskell.org/package/pipes-parse-3.0.1/docs/Pipes-Parse-Tutorial.html pipes-parse>
+ sense.) The remarks that follow in this section are for non-lens adepts.
+
+ Each lens exported here, e.g. 'lines', 'chunksOf' or 'splitAt', reduces to the
+ intuitively corresponding function when used with @view@ or @(^.)@. Instead of
+ writing:
+
+ > splitAt 17 producer
+
+ as we would with the Prelude or Text functions, we write
+
+ > view (splitAt 17) producer
+
+ or equivalently
+
+ > producer ^. splitAt 17
+
+ This may seem a little indirect, but note that many equivalents of
+ @Text -> Text@ functions are exported here as 'Pipe's. Here too we recover the intuitively
+ corresponding functions by prefixing them with @(>->)@. Thus something like
+
+> stripLines = view Text.unlines . Group.maps (>-> Text.stripStart) . view Text.lines
+
+ would drop the leading white space from each line.
+
+ The lenses in this library are marked as /improper/; this just means that
+ they don't admit all the operations of an ideal lens, but only /getting/ and /focusing/.
+ Just for this reason, though, the magnificent complexities of the lens libraries
+ are a distraction. The lens combinators to keep in mind, the ones that make sense for
+ our lenses, are @view@ \/ @(^.)@), @over@ \/ @(%~)@ , and @zoom@.
+
+ One need only keep in mind that if @l@ is a @Lens' a b@, then:
+
+-}
+{- $view
+ @view l@ is a function @a -> b@ . Thus @view l a@ (also written @a ^. l@ )
+ is the corresponding @b@; as was said above, this function will typically be
+ the pipes equivalent of the function you think it is, given its name. So for example
+
+ > view (Text.drop)
+ > view (Text.splitAt 300) :: Producer Text m r -> Producer Text (Producer Text m r)
+ > Text.stdin ^. splitAt 300 :: Producer Text IO (Producer Text IO r)
+
+ I.e., it produces the first 300 characters, and returns the rest of the producer.
+ Thus to uppercase the first n characters
+ of a Producer, leaving the rest the same, we could write:
+
+
+ > upper n p = do p' <- p ^. Text.splitAt n >-> Text.toUpper
+ > p'
+-}
+{- $over
+ @over l@ is a function @(b -> b) -> a -> a@. Thus, given a function that modifies
+ @b@s, the lens lets us modify an @a@ by applying @f :: b -> b@ to
+ the @b@ that we can \"see\" through the lens. So @over l f :: a -> a@
+ (it can also be written @l %~ f@).
+ For any particular @a@, then, @over l f a@ or @(l %~ f) a@ is a revised @a@.
+ So above we might have written things like these:
+
+ > stripLines = Text.lines %~ maps (>-> Text.stripStart)
+ > stripLines = over Text.lines (maps (>-> Text.stripStart))
+ > upper n = Text.splitAt n %~ (>-> Text.toUpper)
+
+-}
+{- $zoom
+ @zoom l@, finally, is a function from a @Parser b m r@
+ to a @Parser a m r@ (or more generally a @StateT (Producer b m x) m r@).
+ Its use is easiest to see with an decoding lens like 'utf8', which
+ \"sees\" a Text producer hidden inside a ByteString producer:
+ @drawChar@ is a Text parser, returning a @Maybe Char@, @zoom utf8 drawChar@ is
+ a /ByteString/ parser, returning a @Maybe Char@. @drawAll@ is a Parser that returns
+ a list of everything produced from a Producer, leaving only the return value; it would
+ usually be unreasonable to use it. But @zoom (splitAt 17) drawAll@
+ returns a list of Text chunks containing the first seventeen Chars, and returns the rest of
+ the Text Producer for further parsing. Suppose that we want, inexplicably, to
+ modify the casing of a Text Producer according to any instruction it might
+ contain at the start. Then we might write something like this:
+
+> obey :: Monad m => Producer Text m b -> Producer Text m b
+> obey p = do (ts, p') <- lift $ runStateT (zoom (Text.splitAt 7) drawAll) p
+> let seven = T.concat ts
+> case T.toUpper seven of
+> "TOUPPER" -> p' >-> Text.toUpper
+> "TOLOWER" -> p' >-> Text.toLower
+> _ -> do yield seven
+> p'
+
+
+> >>> let doc = each ["toU","pperTh","is document.\n"]
+> >>> runEffect $ obey doc >-> Text.stdout
+> THIS DOCUMENT.
+
+ The purpose of exporting lenses is the mental economy achieved with this three-way
+ applicability. That one expression, e.g. @lines@ or @splitAt 17@ can have these
+ three uses is no more surprising than that a pipe can act as a function modifying
+ the output of a producer, namely by using @>->@ to its left: @producer >-> pipe@
+ -- but can /also/ modify the inputs to a consumer by using @>->@ to its right:
+ @pipe >-> consumer@
+
+ The three functions, @view@ \/ @(^.)@, @over@ \/ @(%~)@ and @zoom@ are supplied by
+ both <http://hackage.haskell.org/package/lens lens> and
+ <http://hackage.haskell.org/package/lens-family lens-family> The use of 'zoom' is explained
+ in <http://hackage.haskell.org/package/pipes-parse-3.0.1/docs/Pipes-Parse-Tutorial.html Pipes.Parse.Tutorial>
+ and to some extent in the @Pipes.Text.Encoding@ module here.
+
+-}
+{- $special
+ These simple 'lines' examples reveal a more important difference from @Data.Text.Lazy@ .
+ This is in the types that are most closely associated with our central text type,
+ @Producer Text m r@. In @Data.Text@ and @Data.Text.Lazy@ we find functions like
+
+> splitAt :: Int -> Text -> (Text, Text)
+> lines :: Text -> [Text]
+> chunksOf :: Int -> Text -> [Text]
+
+ which relate a Text with a pair of Texts or a list of Texts.
+ The corresponding functions here (taking account of \'lensification\') are
+
+> view . splitAt :: (Monad m, Integral n) => n -> Producer Text m r -> Producer Text m (Producer Text m r)
+> view lines :: Monad m => Producer Text m r -> FreeT (Producer Text m) m r
+> view . chunksOf :: (Monad m, Integral n) => n -> Producer Text m r -> FreeT (Producer Text m) m r
+
+ Some of the types may be more readable if you imagine that we have introduced
+ our own type synonyms
+
+> type Text m r = Producer T.Text m r
+> type Texts m r = FreeT (Producer T.Text m) m r
+
+ Then we would think of the types above as
+
+> view . splitAt :: (Monad m, Integral n) => n -> Text m r -> Text m (Text m r)
+> view lines :: (Monad m) => Text m r -> Texts m r
+> view . chunksOf :: (Monad m, Integral n) => n -> Text m r -> Texts m r
+
+ which brings one closer to the types of the similar functions in @Data.Text.Lazy@
+
+ In the type @Producer Text m (Producer Text m r)@ the second
+ element of the \'pair\' of effectful Texts cannot simply be retrieved
+ with something like 'snd'. This is an \'effectful\' pair, and one must work
+ through the effects of the first element to arrive at the second Text stream, even
+ if you are proposing to throw the Text in the first element away.
+ Note that we use Control.Monad.join to fuse the pair back together, since it specializes to
+
+> join :: Monad m => Producer Text m (Producer m r) -> Producer m r
+
+ The return type of 'lines', 'words', 'chunksOf' and the other /splitter/ functions,
+ @FreeT (Producer m Text) m r@ -- our @Texts m r@ -- is the type of (effectful)
+ lists of (effectful) texts. The type @([Text],r)@ might be seen to gather
+ together things of the forms:
+
+> r
+> (Text,r)
+> (Text, (Text, r))
+> (Text, (Text, (Text, r)))
+> (Text, (Text, (Text, (Text, r))))
+> ...
+
+ (We might also have identified the sum of those types with @Free ((,) Text) r@
+ -- or, more absurdly, @FreeT ((,) Text) Identity r@.)
+
+ Similarly, our type @Texts m r@, or @FreeT (Text m) m r@ -- in fact called
+ @FreeT (Producer Text m) m r@ here -- encompasses all the members of the sequence:
+
+> m r
+> Text m r
+> Text m (Text m r)
+> Text m (Text m (Text m r))
+> Text m (Text m (Text m (Text m r)))
+> ...
+
+ We might have used a more specialized type in place of @FreeT (Producer a m) m r@,
+ or indeed of @FreeT (Producer Text m) m r@, but it is clear that the correct
+ result type of 'lines' will be isomorphic to @FreeT (Producer Text m) m r@ .
+
+ One might think that
+
+> lines :: Monad m => Lens' (Producer Text m r) (FreeT (Producer Text m) m r)
+> view . lines :: Monad m => Producer Text m r -> FreeT (Producer Text m) m r
+
+ should really have the type
+
+> lines :: Monad m => Pipe Text Text m r
+
+ as e.g. 'toUpper' does. But this would spoil the control we are
+ attempting to maintain over the size of chunks. It is in fact just
+ as unreasonable to want such a pipe as to want
+
+> Data.Text.Lazy.lines :: Text -> Text
+
+ to 'rechunk' the strict Text chunks inside the lazy Text to respect
+ line boundaries. In fact we have
+
+> Data.Text.Lazy.lines :: Text -> [Text]
+> Prelude.lines :: String -> [String]
+
+ where the elements of the list are themselves lazy Texts or Strings; the use
+ of @FreeT (Producer Text m) m r@ is simply the 'effectful' version of this.
+
+ The @Pipes.Group@ module, which can generally be imported without qualification,
+ provides many functions for working with things of type @FreeT (Producer a m) m r@.
+ In particular it conveniently exports the constructors for @FreeT@ and the associated
+ @FreeF@ type -- a fancy form of @Either@, namely
+
+> data FreeF f a b = Pure a | Free (f b)
+
+ for pattern-matching. Consider the implementation of the 'words' function, or
+ of the part of the lens that takes us to the words; it is compact but exhibits many
+ of the points under discussion, including explicit handling of the @FreeT@ and @FreeF@
+ constuctors. Keep in mind that
+
+> newtype FreeT f m a = FreeT (m (FreeF f a (FreeT f m a)))
+> next :: Monad m => Producer a m r -> m (Either r (a, Producer a m r))
+
+ Thus the @do@ block after the @FreeT@ constructor is in the base monad, e.g. 'IO' or 'Identity';
+ the later subordinate block, opened by the @Free@ constructor, is in the @Producer@ monad:
+
+> words :: Monad m => Producer Text m r -> FreeT (Producer Text m) m r
+> words p = FreeT $ do -- With 'next' we will inspect p's first chunk, excluding spaces;
+> x <- next (p >-> dropWhile isSpace) -- note that 'dropWhile isSpace' is a pipe, and is thus *applied* with '>->'.
+> return $ case x of -- We use 'return' and so need something of type 'FreeF (Text m) r (Texts m r)'
+> Left r -> Pure r -- 'Left' means we got no Text chunk, but only the return value; so we are done.
+> Right (txt, p') -> Free $ do -- If we get a chunk and the rest of the producer, p', we enter the 'Producer' monad
+> p'' <- view (break isSpace) -- When we apply 'break isSpace', we get a Producer that returns a Producer;
+> (yield txt >> p') -- so here we yield everything up to the next space, and get the rest back.
+> return (words p'') -- We then carry on with the rest, which is likely to begin with space.
+
+-}
--- /dev/null
+import Pipes
+import Pipes.Text.IO (fromHandle)
+import Pipes.Attoparsec (parsed)
+import qualified System.IO as IO
+
+data Test = Test {
+ a :: Int,
+ b :: Int
+ } deriving (Show)
+
+testParser :: Parser Test
+testParser = do
+ a <- decimal
+ space
+ b <- decimal
+ endOfLine
+ return $ Test a b
+
+main = IO.withFile "./testfile" IO.ReadMode $ \handle -> runEffect $
+ for test_parser (lift . print)
+ where (parsed (testParser <* endOfLine) (fromHandle handle))
\ No newline at end of file
--- /dev/null
+-- http://www.haskellforall.com/2014/02/pipes-parse-30-lens-based-parsing.html
+
+import Data.ByteString (ByteString)
+import Data.Text (Text)
+import Lens.Family.State.Strict (zoom)
+import Pipes
+import Pipes.Parse
+import qualified Pipes.ByteString as ByteString
+import qualified Pipes.Text as Text
+
+-- Retrieve all `Text` chunks up to 10 characters
+parser :: Monad m => Parser ByteString m [Text]
+parser = zoom (Text.decodeUtf8 . Text.splitAt 10) drawAll
+
+main = do
+ (textChunks, leftovers) <- runStateT parser ByteString.stdin
+ print textChunks
+
+ -- Now print the remaining `ByteString` chunks
+ byteChunks <- evalStateT drawAll leftovers
+ print byteChunks
+{-
+$ ./decode
+Hello, 世界!!!<Enter>
+["Hello, \19990\30028!"]
+abcdefg<Enter>
+<Ctrl-D>
+["!!\n","abcdefg\n"]
+
+-}
\ No newline at end of file
--- /dev/null
+{-# LANGUAGE OverloadedStrings #-}
+-- https://gist.github.com/michaelt/88e1fac12876857deefe
+-- following
+-- https://gist.github.com/gelisam/c769d186493221d7ebbe and associated controversy.
+
+module Main where
+
+import Prelude hiding (lines)
+import Lens.Family
+import Pipes
+import Pipes.Group
+import Pipes.HTTP
+import Pipes.Text
+import Pipes.Text.Encoding
+import Pipes.Text.IO (toHandle,stdout)
+import qualified System.IO as IO
+import Data.Functor (void)
+import qualified Data.Text as T
+
+main = do
+ req <- parseUrl "https://gist.github.com/gelisam/c769d186493221d7ebbe"
+ -- "http://www.example.com"
+ -- "http://www.gutenberg.org/files/10/10-h/10-h.htm"
+ withManager tlsManagerSettings $ \m ->
+ withHTTP req m $ \resp -> void $ runEffect $
+ number_lines_of (responseBody resp ^. utf8 . lines) >-> toHandle IO.stdout
+
+number_lines_of :: Monad m => FreeT (Producer Text m) m bad -> Producer Text m bad
+number_lines_of = number_loop (1 :: Int) where
+ number_loop n freeProducers = do
+ freeProducer <- lift $ runFreeT freeProducers
+ case freeProducer of
+ Pure badbytes -> do yield $ T.pack "\n"
+ return badbytes -- these could be inspected ...
+ Free p -> do yield $ T.pack ("\n" ++ show n ++ " ")
+ nextFreeProducers <- p
+ number_loop (n+1) nextFreeProducers
--- /dev/null
+-- this file illustrates several uses of `zoom`
+-- one of them is quadratic in the length of the file
+-- since it has to decode and encode repeatedly,
+-- and is thus no good on long files.
+
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE BangPatterns#-}
+{-# LANGUAGE RankNTypes #-}
+import Blaze.ByteString.Builder (Builder, fromByteString, toByteString)
+import Control.Exception (Exception)
+import Control.Monad.Trans.Class (lift)
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as S
+import qualified Data.ByteString.Lazy as L
+import Data.Monoid
+import Data.Text (Text)
+import qualified Data.Text as T
+import qualified Data.Text.Encoding as TEE
+import qualified Data.Text.Lazy as TL
+import qualified Data.Text.Lazy.Encoding as TLE
+
+import Pipes
+import Pipes.Parse
+import qualified Pipes.Prelude as PP
+import qualified Pipes.ByteString as Bytes
+import qualified Pipes.Text as Txt
+import Pipes.Text.Encoding (utf8)
+
+import Control.Lens
+import Control.Lens.Internal.Zoom
+import Control.Monad
+import qualified System.IO as IO
+import Control.Monad.Trans.Maybe
+import Control.Monad.State.Class
+
+main :: IO ()
+main = do -- S.writeFile fp $ contents 10000 -- 10000 cannot be handled fileParser0 and 1
+ -- parse_file fileParser0 -- pathological
+ -- parse_file fileParser1 -- programs
+ parse_file fileParser2 -- good program
+
+ where
+ parse_file parser = IO.withBinaryFile fp IO.ReadMode $ \h ->
+ do p' <- runEffect $ parseWith parser ( Bytes.fromHandle h ) >-> PP.print
+ runEffect $ p' >-> PP.print
+ parseWith parser = loop where
+ loop p = do (m,p') <- lift (runStateT (runMaybeT parser) p)
+ case m of Nothing -> return p'
+ Just file -> do yield file
+ loop p'
+ fp = "encoded.fileformat"
+ contents n = (toByteString . mconcat . replicate n . encodeFiles) input
+ <> S.pack (replicate 10 250)
+
+
+
+fileParser0, fileParser1, fileParser2 :: Monad m => MaybeT (StateT (Producer ByteString m x) m) File
+fileParser0 = do (name, len) <- zoom utf8 parseText
+ contents <- zoom (Bytes.splitAt len) (lift drawAll)
+ return (File name (S.concat contents))
+ where
+ -- this parser aggregates all Text parsing into one preliminary parser
+ -- which is then applied with `zoom utf8`
+ -- we cannot tell in advance how long, e.g. the file name will be
+ parseText :: Monad m => MaybeT (StateT (Producer Text m x) m) (Text, Int)
+ parseText = do nameLength <- parseNumber
+ names <- zoom (Txt.splitAt nameLength) $ (lift drawAll)
+ contentLength <- parseNumber
+ return $! (T.concat names, contentLength)
+
+-- here we disaggregate the little Text parsers but still apply them with `zoom utf8`
+-- this makes no difference
+fileParser1 = do nameLength <- zoom utf8 parseNumber
+ names <- zoom (utf8 . Txt.splitAt nameLength) (lift drawAll)
+ contentLength <- zoom utf8 parseNumber
+ contents <- zoom (Bytes.splitAt contentLength) (lift drawAll)
+ return (File (T.concat names) (S.concat contents))
+
+-- this is the good program; be reflecting on the fact that file names
+-- should not be a 1000 bytes long, and binary files longer than e.g. 10 ^ 10
+-- we can restrict the length of the byte stream to which we apply `zoom utf8`
+fileParser2 = do nameLength <- Bytes.splitAt 3 ~~> utf8 ~~> parseNumber
+ names <- Bytes.splitAt nameLength ~~> utf8 ~~> lift drawAll
+ len <- Bytes.splitAt 10 ~~> utf8 ~~> parseNumber
+ contents <- Bytes.splitAt len ~~> lift drawAll
+ return (File (T.concat names) (S.concat contents))
+
+-- infix lens nonsense
+infixr 1 ~~>
+(~~>) :: Zoom m n s t
+ => ((s -> Zoomed n c s) -> t -> Zoomed n c t)
+ -> m c -> n c
+(~~>) = zoom
+{-# INLINE (~~>) #-}
+
+parseNumber :: Monad m => MaybeT (StateT (Producer Text m x) m) Int
+parseNumber = loop 0 where
+ loop !n = do c <- MaybeT Txt.drawChar
+ case c of ':' -> return n
+ _ -> do guard ('0' <= c && c <= '9')
+ loop $! n * 10 + (fromEnum c - fromEnum '0')
+
+
+
+-- --- Michael S's `File` type and its binary encoding, etc.
+
+
+data File = File
+ { fileName :: !Text
+ , fileContents :: !ByteString
+ }
+ deriving Show
+
+encodeFile :: File -> Builder
+encodeFile (File name contents) =
+ tellLength (S.length bytesname) <>
+ fromByteString bytesname <>
+ tellLength (S.length contents) <>
+ fromByteString contents
+ where
+ tellLength i = fromByteString $ TEE.encodeUtf8 (T.pack (shows i ":"))
+ bytesname = TEE.encodeUtf8 name
+
+encodeFiles :: [File] -> Builder
+encodeFiles = mconcat . map encodeFile
+
+input :: [File]
+input =
+ [ File "utf8.txt" $ TEE.encodeUtf8 "This file is in UTF-8"
+ , File "utf16.txt" $ TEE.encodeUtf16LE "This file is in UTF-16"
+ , File "binary.dat" "we'll pretend to be binary"
+ ]
+
+
+---
+
+-- This desperate scheme actually has some efficacy, if used before `utf8` in a zoom
+-- but not much
+
+chunk :: Monad m => Int -> Lens' (Producer ByteString m r) (Producer ByteString m r)
+chunk n = lens (chunkyN n) (\_ b -> b) where
+
+ chunkyN :: Monad m => Int -> Producer ByteString m r -> Producer ByteString m r
+ chunkyN n = prod_loop where
+
+ prod_loop p = do mbs <- lift $ next p
+ case mbs of Left r -> return r
+ Right (bs, p') -> do bs_loop bs
+ prod_loop p'
+ bs_loop bs = unless (S.null bs) $ do yield fore
+ unless (S.null aft) (bs_loop aft)
+ where (fore, aft) = S.splitAt n bs
if !flag(noio)
exposed-modules: Pipes.Text.IO
build-depends: text >=0.11.3 && < 1.2
-
projects / github / fretlink / text-pipes.git / commitdiff
