ReadArgs: Simple command line argument parsing
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. Both Char
and String
are handled specially so that
command line arguments for both do not require quotes (as their
Read
instances do).
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
Downloads
- ReadArgs-1.1.tar.gz [browse] (Cabal source package)
- Package description (as included in the package)
Maintainer's Corner
For package maintainers and hackage trustees
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Versions [RSS] | 1.0, 1.1, 1.2, 1.2.1, 1.2.2, 1.2.3 |
---|---|
Dependencies | base (>=4.3.1.0 && <5) [details] |
License | BSD-3-Clause |
Author | Noah Luck Easterly |
Maintainer | noah.easterly@gmail.com |
Category | Command Line |
Home page | http://github.com/rampion/ReadArgs |
Source repo | head: git clone git://github.com/rampion/ReadArgs.git |
Uploaded | by NoahEasterly at 2012-01-06T18:05:44Z |
Distributions | Debian:1.2.3, FreeBSD:1.2.2, NixOS:1.2.3 |
Reverse Dependencies | 3 direct, 272 indirect [details] |
Executables | ReadArgsEx |
Downloads | 21022 total (20 in the last 30 days) |
Rating | (no votes yet) [estimated by Bayesian average] |
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Status | Docs uploaded by user Build status unknown [no reports yet] |