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Through the lens of Haskell
Exploring new ideas for library design
Through the lens of Haskell Exploring new ideas for library design - - PowerPoint PPT Presentation
Through the lens of Haskell Exploring new ideas for library design - - PowerPoint PPT Presentation
Through the lens of Haskell Exploring new ideas for library design @georgesdubus Haskell, the language Haskell, the ecosystem Design space There should be one and preferably only one obvious way to do it. (Python) There should be
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Haskell, the language
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Haskell, the ecosystem
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Design space
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There should be one — and preferably only one —
- bvious way to do it.
(Python)
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There should be one — and preferably only one —
- bvious way to do it.
Let’s keep looking for it!
(Python) (Haskell)
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Some Haskell libraries
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JSON Packaging HTTP
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JSON Packaging HTTP ??? ??? ???
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Some Haskell libraries
Part 1: attoparsec
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“Real life” use case :
A slack bot that answers movie quotes
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subtitleParser Full package definition
Name Type
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subtitleParser All I need
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attoparsec
All I need to know :
parseOnly :: Parser Subtitles -> ByteString -> Either ErrorMessage Subtitles
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attoparsec
All I need to know :
parseOnly :: Parser Subtitles -> ByteString -> Either ErrorMessage Subtitles parseOnly :: Parser a -> ByteString -> Either ErrorMessage a
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attoparsec
Or : incremental parsing
parse :: Parser a -> ByteString -> Result a feed :: Result a -> ByteString -> Result a
(Result can be Partial, Failed or Done)
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attoparsec
Part of a bigger parser
many :: Parser a -> Parser [a]
- r :: Parser a -> Parser b -> Parser (Either a b)
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Parsers everywhere
parseCSV :: Parser CSV in attoparsec-csv json :: Parser JSONValue in aeson crontab :: Parser Crontab in cron emailAddress :: Parser String in email-header toml :: Parser TOMLValue in toml ...
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A good library simplifies the implementation
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A good library simplifies the interface
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General solution Specific building blocks
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General solution Specific building blocks
attoparsec all parsers
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Some Haskell libraries
Part 2: conduit
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Conduit
Streaming library Producers Consumers Conduits that both consume and produce
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Lot of libraries
sourceSocket socket =$= ungzip =$= sinkFile "/tmp/output" producer from Data.Conduit.Network conduit from Data.Conduit.Zlib consumer from Data.Conduit.Binary
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conduit + attoparsec =
High-performance subtitles streaming for free !
sourceFile “something.srt” =$= conduitParser parseSubtitleLine =$= ircConsumer
Parser of Subtitle Lines Parser ➡ Conduit
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General solution Specific building blocks
conduit all conduits
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Some Haskell libraries
Part 3: lens
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BlogPost { title = “Made-up examples considered harmful” , author = Person {name=“Alice”} , comments = [ Comment { author = “Bob” , content = “Great insight!” } , Comment { author = “Carol” , content = “I completely disagree” } ] }
Data manipulation
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>>> view title blogpost “Made-up examples considered harmful”
Getters
Lens
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>>> view title blogpost “Made-up examples considered harmful” >>> view (author . name) blogpost "Alice"
Getters
Lens Lens Lens
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>>> view title blogpost “Made-up examples considered harmful” >>> view (author . name) blogpost "Alice" >>> set (speaker . name) “Alicia” blogpost BlogPost { title = “Made-up examples considered harmful” , author = “Alicia” , ... }
Getters Setters
Lens Lens Lens
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>>> toListOf (comments . each . author) blogpost [“Bob”, “Carol”]
Getters/setters with multiple values ?!?
Lens Lens Traversal
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>>> let commentContents = comments . each . content >>> toListOf commentContents blogpost [“Great insight!”, “I completely disagree”] >>> set commentContents “Blah blah blah” blogpost BlogPost { comments = [ Comment { author = “Bob” , content = “Blah blah blah” } , Comment { author = “Carol” , content = “Blah blah blah” } ] , ... }
Getter / setter pairs are values
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[{“id”: “1”, “name”: “georges”}, {“id”: “2”, “name”: “lucie”}] >>> input & (values . key “name”) %~ capitalize [{“id”: “1”, “name”: “Georges”}, {“id”: “2”, “name”: “Lucie”}]
Libraries provide lenses: JSON
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titles = allNamed (only "h2") . contents
Libraries provide lenses: HTML
Traversal into all tags with a given name Their content
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General solution Specific building blocks
lens all lenses
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“Borrowing” ideas
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Python ➡ Haskell wreq = requests + lens
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Haskell ➡ Python hypothesis
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Conclusion
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Explore the design space
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Explore the design space Factorize library interfaces
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