This module provides simple command line argument processing.
The main function of interest is cmdArgs
.
A simple example is:
data Sample = Sample {hello :: String} deriving (Show, Data, Typeable)
sample = Sample{hello =
def
&=
help
"World argument" &=
opt
"world"}
&=
summary "Sample v1"
main = print =<< cmdArgs
sample
Attributes are used to control a number of behaviours:
- The help message:
help
,typ
,details
,summary
,program
,groupname
- Flag behaviour:
opt
,enum
,verbosity
- Flag name assignment:
name
,explicit
- Controlling non-flag arguments:
args
,argPos
- multi-mode programs:
modes
,auto
- Supported Types
- Each field in the record must be one of the supported
atomic types (
String
,Int
,Integer
,Float
,Double
,Bool
) or a list ([]
) orMaybe
wrapping at atomic type. - Missing Fields
- If a field is shared by multiple modes, it may be omitted in subsequent modes, and will default to the previous value.
Warning: Values created with annotations are not pure - the first
time they are used they will include the annotations, but subsequently
they will not. To capture the annotations, so they can be used multiple times,
use cmdArgsMode
.
- cmdArgs :: Data a => a -> IO a
- cmdArgsMode :: Data a => a -> Mode (CmdArgs a)
- cmdArgsRun :: Mode (CmdArgs a) -> IO a
- cmdArgsApply :: CmdArgs a -> IO a
- data CmdArgs a = CmdArgs {
- cmdArgsValue :: a
- cmdArgsHelp :: Maybe String
- cmdArgsVersion :: Maybe String
- cmdArgsVerbosity :: Maybe Verbosity
- cmdArgsPrivate :: CmdArgsPrivate
- (&=) :: Data a => a -> Ann -> a
- modes :: Data a => [a] -> a
- enum :: Data a => [a] -> a
- opt :: (Show a, Typeable a) => a -> Ann
- typ :: String -> Ann
- typFile :: Ann
- typDir :: Ann
- help :: String -> Ann
- name :: String -> Ann
- args :: Ann
- argPos :: Int -> Ann
- groupname :: String -> Ann
- details :: [String] -> Ann
- summary :: String -> Ann
- auto :: Ann
- program :: String -> Ann
- explicit :: Ann
- verbosity :: Ann
- module System.Console.CmdArgs.Verbosity
- module System.Console.CmdArgs.Default
- data Ann
- data Mode a
- class Typeable a => Data a
- class Typeable a
Running command lines
cmdArgs :: Data a => a -> IO aSource
Take annotated records and run the corresponding command line.
Shortcut for
.
cmdArgsRun
. cmdArgsMode
cmdArgsMode :: Data a => a -> Mode (CmdArgs a)Source
Take annotated records and turn them in to a Mode
value, that can
make use of the System.Console.CmdArgs.Explicit functions (i.e. process
).
Annotated records are impure, and will only contain annotations on their first use. The result of this function is pure, and can be reused.
cmdArgsRun :: Mode (CmdArgs a) -> IO aSource
Run a Mode structure. This function reads the command line arguments and then performs as follows:
- If invalid arguments are given, it will display the error message and exit.
- If
--help
is given, it will display the help message and exit. - If
--version
is given, it will display the version and exit. - In all other circumstances the program will return a value.
- Additionally, if either
--quiet
or--verbose
is given (seeverbosity
) it will set the verbosity (seesetVerbosity
).
cmdArgsApply :: CmdArgs a -> IO aSource
Perform the necessary actions dictated by a CmdArgs
structure.
- If
cmdArgsHelp
isJust
, it will display the help message and exit. - If
cmdArgsVersion
isJust
, it will display the version and exit. - In all other circumstances it will return a value.
- Additionally, if
cmdArgsVerbosity
isJust
(seeverbosity
) it will set the verbosity (seesetVerbosity
).
A structure to store the additional data relating to --help
,
--version
, --quiet
and --verbose
.
CmdArgs | |
|
Constructing command lines
Attributes can work on a flag (inside a field), on a mode (outside the record),
or on all modes (outside the modes
call).
(&=) :: Data a => a -> Ann -> aSource
Add an annotation to a value. Note that if the value is evaluated more than once the annotation will only be available the first time.
modes :: Data a => [a] -> aSource
Modes: "I want a program with multiple modes, like darcs or cabal."
Takes a list of modes, and creates a mode which includes them all.
If you want one of the modes to be chosen by default, see auto
.
data Modes = Mode1 | Mode2 | Mode3 deriving Data cmdArgs $ modes [Mode1,Mode2,Mode3]
enum :: Data a => [a] -> aSource
Flag: "I want several different flags to set this one field to different values."
This annotation takes a type which is an enumeration, and provides multiple separate flags to set the field to each value.
data State = On | Off deriving Data data Mode = Mode {state :: State} cmdArgs $ Mode {state = enum [On &= help "Turn on",Off &= help "Turn off"]} --on Turn on --off Turn off
opt :: (Show a, Typeable a) => a -> AnnSource
Flag: "I want users to be able to omit the value for this flag."
Make the value of a flag optional. If --flag
is given, it will
be treated as --flag=this_argument
.
{hello = def &= opt "foo"} -h --hello[=VALUE] (default=foo)
Flag/Mode: "The help message is ..."
Descriptive text used in the help output.
{hello = def &= help "Help message"} -h --hello=VALUE Help message
Flag: "Use this flag name for this field."
Add flags which trigger this option.
{hello = def &= name "foo"} -h --hello --foo=VALUE
Flag: "Put the nth non-flag argument here."
This field should be used to store a particular argument position (0-based).
{hello = def &= argPos 0}
groupname :: String -> AnnSource
Flag/Mode: "Give these flags/modes a group name in the help output."
This mode will be used for all following modes/flags, until the
next groupname
.
{hello = def &= groupname "Welcomes"} Welcomes -h --hello=VALUE
details :: [String] -> AnnSource
Mode: "A longer description of this mode is ..."
Suffix to be added to the help message.
Sample{..} &= details ["More details on the website www.example.org"]
summary :: String -> AnnSource
Modes: "My program name/version/copyright is ..."
One line summary of the entire program, the first line of
--help
and the only line of --version
.
Sample{..} &= summary "CmdArgs v0.0, (C) Neil Mitchell 1981"
Mode: "If the user doesn't give a mode, use this one."
This mode is the default. If no mode is specified and a mode has this attribute then that mode is selected, otherwise an error is raised.
modes [Mode1{..}, Mode2{..} &= auto, Mode3{..}]
program :: String -> AnnSource
Modes: "My program executable is named ..."
This is the name of the program executable. Only used in the help message. Defaults to the type of the mode.
Sample{..} &= program "sample"
Flag: "Don't guess any names for this field."
A field should not have any flag names guessed for it.
All flag names must be specified by flag
.
{hello = def &= explicit &= flag "foo"} --foo=VALUE
Re-exported for convenience
Provides a few opaque types (for writing type signatures),
verbosity control, default values with def
and the
Data
/Typeable
type classes.
The general type of annotations that can be associated with a value.
A mode. Each mode has three main features:
- A list of submodes (
modeGroupModes
) - A list of flags (
modeGroupFlags
) - Optionally an unnamed argument (
modeArgs
)
The Data
class comprehends a fundamental primitive gfoldl
for
folding over constructor applications, say terms. This primitive can
be instantiated in several ways to map over the immediate subterms
of a term; see the gmap
combinators later in this class. Indeed, a
generic programmer does not necessarily need to use the ingenious gfoldl
primitive but rather the intuitive gmap
combinators. The gfoldl
primitive is completed by means to query top-level constructors, to
turn constructor representations into proper terms, and to list all
possible datatype constructors. This completion allows us to serve
generic programming scenarios like read, show, equality, term generation.
The combinators gmapT
, gmapQ
, gmapM
, etc are all provided with
default definitions in terms of gfoldl
, leaving open the opportunity
to provide datatype-specific definitions.
(The inclusion of the gmap
combinators as members of class Data
allows the programmer or the compiler to derive specialised, and maybe
more efficient code per datatype. Note: gfoldl
is more higher-order
than the gmap
combinators. This is subject to ongoing benchmarking
experiments. It might turn out that the gmap
combinators will be
moved out of the class Data
.)
Conceptually, the definition of the gmap
combinators in terms of the
primitive gfoldl
requires the identification of the gfoldl
function
arguments. Technically, we also need to identify the type constructor
c
for the construction of the result type from the folded term type.
In the definition of gmapQ
x combinators, we use phantom type
constructors for the c
in the type of gfoldl
because the result type
of a query does not involve the (polymorphic) type of the term argument.
In the definition of gmapQl
we simply use the plain constant type
constructor because gfoldl
is left-associative anyway and so it is
readily suited to fold a left-associative binary operation over the
immediate subterms. In the definition of gmapQr, extra effort is
needed. We use a higher-order accumulation trick to mediate between
left-associative constructor application vs. right-associative binary
operation (e.g., (:)
). When the query is meant to compute a value
of type r
, then the result type withing generic folding is r -> r
.
So the result of folding is a function to which we finally pass the
right unit.
With the -XDeriveDataTypeable
option, GHC can generate instances of the
Data
class automatically. For example, given the declaration
data T a b = C1 a b | C2 deriving (Typeable, Data)
GHC will generate an instance that is equivalent to
instance (Data a, Data b) => Data (T a b) where
gfoldl k z (C1 a b) = z C1 `k` a `k` b
gfoldl k z C2 = z C2
gunfold k z c = case constrIndex c of
1 -> k (k (z C1))
2 -> z C2
toConstr (C1 _ _) = con_C1
toConstr C2 = con_C2
dataTypeOf _ = ty_T
con_C1 = mkConstr ty_T "C1" [] Prefix
con_C2 = mkConstr ty_T "C2" [] Prefix
ty_T = mkDataType "Module.T" [con_C1, con_C2]
This is suitable for datatypes that are exported transparently.
Data Bool | |
Data Char | |
Data Double | |
Data Float | |
Data Int | |
Data Int8 | |
Data Int16 | |
Data Int32 | |
Data Int64 | |
Data Integer | |
Data Ordering | |
Data Word | |
Data Word8 | |
Data Word16 | |
Data Word32 | |
Data Word64 | |
Data () | |
Data Verbosity | |
Data CmdArgsPrivate | |
Data a => Data [a] | |
(Data a, Integral a) => Data (Ratio a) | |
Typeable a => Data (Ptr a) | |
Typeable a => Data (ForeignPtr a) | |
Data a => Data (Maybe a) | |
Data a => Data (CmdArgs a) | |
(Data a, Data b) => Data (Either a b) | |
(Data a, Data b) => Data (a, b) | |
(Typeable a, Data b, Ix a) => Data (Array a b) | |
(Data a, Data b, Data c) => Data (a, b, c) | |
(Data a, Data b, Data c, Data d) => Data (a, b, c, d) | |
(Data a, Data b, Data c, Data d, Data e) => Data (a, b, c, d, e) | |
(Data a, Data b, Data c, Data d, Data e, Data f) => Data (a, b, c, d, e, f) | |
(Data a, Data b, Data c, Data d, Data e, Data f, Data g) => Data (a, b, c, d, e, f, g) |
class Typeable a
The class Typeable
allows a concrete representation of a type to
be calculated.