ghc-ReadArgs

ReadArgs provides the 'readArgs' IO action, which lets you tell the compiler to
parse the command line arguments to fit the type signature you give.
For example '(a :: Int, b :: String, c :: Float) <- readArgs' would parse the
first runtime argument as an 'Int', the second as a 'String' (no quotes
required) and the third as a 'Float'.
If the runtime arguments are incompatible with the type signature, then a
simple usage statement is given of the types needed.
Continuing the previous example, if it was used in a program named 'Example',
the error message for the above action would be:
' usage: Example Int String Float '
Any type that has both 'Typeable' and 'Read' instances can be used.
'Char', 'String', and 'Text' are handled specially so that command line
arguments for both do not require quotes (as their 'Read' instances do).
A special instance is provided for 'FilePath' so that no constructor or quotes
are required.
'readArgs' also supports optional arguments and variadic arguments.
Optional arguments are specified using 'Maybe', and variadic arguments using a
list. '(a :: Int, b :: Maybe String, c :: [Float]) <- readArgs' would
successfully parse any of the following sets of command line arguments:
' Example 1 Example 1 2 3 4 Example 1 foo Example 1 foo 2 3 4 '
But not
' Example Example foo Example 1.0 '
Usage statements for optional and variadic arguments use command-line parlance:
' usage: Example Int [String] [Float..] '
Note that both optional and variadic parsers are greedy by default (so 'Example
1 2 3 4' was parsed as '(1, "2", [3.0,4.0])'. They may both be made non-greedy
through use of the 'NonGreedy' constructor:
' ( a :: Int , NonGreedy b :: NonGreedy Maybe String , NonGreedy c :: NonGreedy
[] Float ) <- readArgs '.

          

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License: BSD-3-Clause
URL: https://hackage.haskell.org/package/ReadArgs