69 lines
2.4 KiB
XML
69 lines
2.4 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
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<pkgmetadata>
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<herd>haskell</herd>
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<maintainer>
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<email>haskell@gentoo.org</email>
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</maintainer>
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<longdescription>
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Here is a simple example of an applicative option parser:
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@
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data Sample = Sample
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&#x20; &#x7b; hello :: String
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&#x20; , quiet :: Bool &#x7d;
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sample :: Parser Sample
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sample = Sample
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&#x20; \<$\> strOption
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&#x20; ( long \"hello\"
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&#x20; & metavar \"TARGET\"
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&#x20; & help \"Target for the greeting\" )
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&#x20; \<*\> switch
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&#x20; ( long \"quiet\"
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&#x20; & help \"Whether to be quiet\" )
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@
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The parser is built using applicative style starting from a set of basic
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combinators. In this example, @hello@ is defined as an 'option' with a
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@String@ argument, while @quiet@ is a boolean 'flag' (called 'switch').
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A parser can be used like this:
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@
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greet :: Sample -> IO ()
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greet (Sample h False) = putStrLn $ \"Hello, \" ++ h
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greet _ = return ()
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main :: IO ()
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main = execParser opts \>\>= greet
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&#x20; where
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&#x20; opts = info (helper \<*\> sample)
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&#x20; ( fullDesc
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&#x20; & progDesc \"Print a greeting for TARGET\"
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&#x20; & header \"hello - a test for optparse-applicative\" )
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@
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The @greet@ function is the entry point of the program, while @opts@ is a
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complete description of the program, used when generating a help text. The
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'helper' combinator takes any parser, and adds a @help@ option to it (which
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always fails).
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The @hello@ option in this example is mandatory (since it doesn't have a
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default value), so running the program without any argument will display a
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help text:
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>hello - a test for optparse-applicative
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>
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>Usage: hello --hello TARGET [--quiet]
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> Print a greeting for TARGET
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>
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>Available options:
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> -h,--help Show this help text
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> --hello TARGET Target for the greeting
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> --quiet Whether to be quiet
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containing a short usage summary, and a detailed list of options with
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descriptions.
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</longdescription>
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</pkgmetadata>
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