dev-haskell/optparse-applicative/metadata.xml


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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
	<herd>haskell</herd>
	<maintainer>
		<email>haskell@gentoo.org</email>
	</maintainer>
	<longdescription>
		Here is a simple example of an applicative option parser:
		
		@
		data Sample = Sample
		&amp;#x20; &amp;#x7b; hello :: String
		&amp;#x20; , quiet :: Bool &amp;#x7d;
		
		sample :: Parser Sample
		sample = Sample
		&amp;#x20; \&lt;$\&gt; strOption
		&amp;#x20;     ( long \&quot;hello\&quot;
		&amp;#x20;     &amp; metavar \&quot;TARGET\&quot;
		&amp;#x20;     &amp; help \&quot;Target for the greeting\&quot; )
		&amp;#x20; \&lt;*\&gt; switch
		&amp;#x20;     ( long \&quot;quiet\&quot;
		&amp;#x20;     &amp; help \&quot;Whether to be quiet\&quot; )
		@
		
		The parser is built using applicative style starting from a set of basic
		combinators. In this example, @hello@ is defined as an &#39;option&#39; with a
		@String@ argument, while @quiet@ is a boolean &#39;flag&#39; (called &#39;switch&#39;).
		
		A parser can be used like this:
		
		@
		greet :: Sample -&gt; IO ()
		greet (Sample h False) = putStrLn $ \&quot;Hello, \&quot; ++ h
		greet _ = return ()
		
		main :: IO ()
		main = execParser opts \&gt;\&gt;= greet
		&amp;#x20; where
		&amp;#x20;   opts = info (helper \&lt;*\&gt; sample)
		&amp;#x20;     ( fullDesc
		&amp;#x20;     &amp; progDesc \&quot;Print a greeting for TARGET\&quot;
		&amp;#x20;     &amp; header \&quot;hello - a test for optparse-applicative\&quot; )
		@
		
		The @greet@ function is the entry point of the program, while @opts@ is a
		complete description of the program, used when generating a help text. The
		&#39;helper&#39; combinator takes any parser, and adds a @help@ option to it (which
		always fails).
		
		The @hello@ option in this example is mandatory (since it doesn&#39;t have a
		default value), so running the program without any argument will display a
		help text:
		
		&gt;hello - a test for optparse-applicative
		&gt;
		&gt;Usage: hello --hello TARGET [--quiet]
		&gt;  Print a greeting for TARGET
		&gt;
		&gt;Available options:
		&gt;  -h,--help                Show this help text
		&gt;  --hello TARGET           Target for the greeting
		&gt;  --quiet                  Whether to be quiet
		
		containing a short usage summary, and a detailed list of options with
		descriptions.
	</longdescription>
</pkgmetadata>