cmdargs-0.9: Command line argument processing




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:

Supported Types: Each field in the record must be one of the supported atomic types (String, Int, Integer, Float, Double, Bool, an enumeration, a tuple of atomic types) or a list ([]) or Maybe 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.

Purity: Values created with annotations are not pure - the first time they are computed they will include the annotations, but subsequently they will not. If you wish to run the above example in a more robust way:

sample = cmdArgsMode $ Sample{hello = ... -- as before
main = print =<< cmdArgsRun sample

Even using this scheme, sometimes GHC's optimisations may share values who have the same annotation. To disable sharing you may need to specify {-# OPTIONS_GHC -fno-cse #-} in the module you define the flags.

Pure annotations: Alternatively, you may use pure annotations, which are referentially transparent, but less type safe and more verbose. The initial example may be written as:

sample = record Sample{} [hello := def += help "World argument" += opt "world"] += summary "Sample v1"

main = print =<< (cmdArgs_ sample :: IO Sample)

All the examples are written using impure annotations. To convert to pure annotations follow the rules:

 Ctor {field1 = value1 &= ann1, field2 = value2} &= ann2 ==> record Ctor{} [field1 := value1 += ann1, field2 := value2] += ann2
 Ctor (value1 &= ann1) value2 &= ann2 ==> record Ctor{} [atom value1 += ann1, atom value2] += ann2
 modes [Ctor1{...}, Ctor2{...}] ==> modes_ [record Ctor1{} [...], record Ctor2{} [...]]
 Ctor {field1 = enum [X &= ann, Y]} ==> record Ctor{} [enum_ field1 [atom X += ann, atom Y]]

If you are willing to use TemplateHaskell, you can write in the impure syntax, but have your code automatically translated to the pure style. For more details see System.Console.CmdArgs.Quote.


Running command lines

cmdArgs :: Data a => a -> IO aSource

Take impurely annotated records and run the corresponding command line. Shortcut for cmdArgsRun . cmdArgsMode.

To use cmdArgs with custom command line arguments see System.Environment.withArgs.

cmdArgsMode :: Data a => a -> Mode (CmdArgs a)Source

Take impurely 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 (see verbosity) it will set the verbosity (see setVerbosity).

cmdArgs_ :: Data a => Annotate Ann -> IO aSource

Take purely annotated records and run the corresponding command line. Shortcut for cmdArgsRun . cmdArgsMode_.

To use cmdArgs_ with custom command line arguments see System.Environment.withArgs.

cmdArgsMode_ :: Data a => Annotate Ann -> Mode (CmdArgs a)Source

Take purely annotated records and turn them in to a Mode value, that can make use of the System.Console.CmdArgs.Explicit functions (i.e. process).

cmdArgsApply :: CmdArgs a -> IO aSource

Perform the necessary actions dictated by a CmdArgs structure.

data CmdArgs a Source

A structure to store the additional data relating to --help, --version, --quiet and --verbose.




cmdArgsValue :: a

The underlying value being wrapped.

cmdArgsHelp :: Maybe String

Just if --help is given, then gives the help message for display, including a trailing newline.

cmdArgsVersion :: Maybe String

Just if --version is given, then gives the version message for display, including a trailing newline.

cmdArgsVerbosity :: Maybe Verbosity

Just if --quiet or --verbose is given, then gives the verbosity to use.

cmdArgsPrivate :: CmdArgsPrivate

Private: Only exported due to Haddock limitations.


Functor CmdArgs 
Typeable1 CmdArgs 
Eq a => Eq (CmdArgs a) 
Data a => Data (CmdArgs a) 
Ord a => Ord (CmdArgs a) 
Show a => Show (CmdArgs a) 

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).

opt :: (Show a, Typeable a) => a -> AnnSource

Flag: "I want users to be able to omit the value associated with 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)

Note that all flags in CmdArgs are optional, and if omitted will use their default value. Those annotated with opt also allow the flag to be present without an associated value. As an example:

 {hello = "DEFAULT" &= opt "OPTIONAL"}
 $ main
 {hello = "DEFAULT"}
 $ main --hello
 {hello = "OPTIONAL"}
 $ main --hello=VALUE
 {hello = "VALUE"}

typ :: String -> AnnSource

Flag: "For this flag, users need to give something of type ..."

The the type of a flag's value, usually upper case. Only used for the help message. Commonly the type will be FILE (typFile) or DIR (typDir).

 {hello = def &= typ "MESSAGE"}
   -h --hello=MESSAGE

typFile :: AnnSource

Flag: "Users must give a file for this flag's value."

Alias for typ FILE.

typDir :: AnnSource

Flag: "Users must give a directory for this flag's value."

Alias for typ DIR.

help :: String -> AnnSource

Flag/Mode: "The help message is ..."

Descriptive text used in the help output.

 {hello = def &= help "Help message"}
   -h --hello=VALUE      Help message

name :: String -> AnnSource

Flag: "Use this flag name for this field."

Add flags which trigger this option.

 {hello = def &= name "foo"}
   -h --hello --foo=VALUE

args :: AnnSource

Flag: "Put non-flag arguments here."

 {hello = def &= args}

argPos :: Int -> AnnSource

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"}
   -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"]

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"

auto :: AnnSource

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"

explicit :: AnnSource

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 &= name "foo"}

ignore :: AnnSource

Flag/Mode: "Ignore this field, don't let the user set it."

A mode or field is not dealt with by CmdArgs.

 {hello = def, extra = def &= ignore}

verbosity :: AnnSource

Modes: "My program needs verbosity flags."

Add --verbose and --quiet flags.

helpArg :: [Ann] -> AnnSource

Modes: "Customise the help argument."

Add extra options to a help argument, such as help, name, ignore or explicit.

 Sample{..} &= helpArg [explicit, name "h"]

versionArg :: [Ann] -> AnnSource

Modes: "Customise the version argument."

Add extra options to a version argument, such as help, name, ignore, summary or explicit.

 Sample{..} &= versionArg [ignore]

verbosityArgs :: [Ann] -> [Ann] -> AnnSource

Modes: "Customise the verbosity arguments."

Add extra options to a verbosity arguments (--verbose and --quiet), such as help, name, ignore or explicit. The verbose options come first, followed by the quiet options.

 Sample{..} &= verbosityArgs [ignore] [name "silent", explicit]


(&=) :: Data val => val -> Ann -> valSource

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 val => [val] -> valSource

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 val => [val] -> valSource

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


(+=) :: Annotate ann -> ann -> Annotate annSource

Add an annotation to a value.

record :: Data a => a -> [Annotate ann] -> Annotate annSource

Create a constructor/record. The first argument should be the type of field, the second should be a list of fields constructed originally defined by := or :=+.

This operation is not type safe, and may raise an exception at runtime if any field has the wrong type or label.

atom :: Data val => val -> Annotate annSource

Lift a pure value to an annotation.

data Annotate ann Source

This type represents an annotated value. The type of the underlying value is not specified.


forall c f . (Data c, Data f) => (c -> f) := f

Construct a field, fieldname := value.


enum_ :: (Data c, Data f) => (c -> f) -> [Annotate Ann] -> Annotate AnnSource

Like enum, but using the pure annotations.

modes_ :: [Annotate Ann] -> Annotate AnnSource

Like modes, but using the pure annotations.

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.

data Ann Source

The general type of annotations that can be associated with a value.


data Mode a Source

A mode. Each mode has three main features:


Remap Mode 
Show (Mode a) 
Packer a => Packer (Mode a) 

class Typeable a => Data a

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 gmapQx 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 Exp 
Data Match 
Data Clause 
Data Pat 
Data Type 
Data Dec 
Data Name 
Data FunDep 
Data Pred 
Data TyVarBndr 
Data () 
Data NameFlavour

Although the NameFlavour type is abstract, the Data instance is not. The reason for this is that currently we use Data to serialize values in annotations, and in order for that to work for Template Haskell names introduced via the 'x syntax we need gunfold on NameFlavour to work. Bleh!

The long term solution to this is to use the binary package for annotation serialization and then remove this instance. However, to do _that_ we need to wait on binary to become stable, since boot libraries cannot be upgraded seperately from GHC itself.

This instance cannot be derived automatically due to bug #2701

Data NameSpace 
Data Info 
Data ClassInstance 
Data Fixity 
Data FixityDirection 
Data Lit 
Data Body 
Data Guard 
Data Stmt 
Data Range 
Data FamFlavour 
Data Foreign 
Data Callconv 
Data Safety 
Data Pragma 
Data InlineSpec 
Data Strict 
Data Con 
Data Kind 
Data ModName 
Data PkgName 
Data OccName 
Data Ann 
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.


Typeable Bool 
Typeable Char 
Typeable Double 
Typeable Float 
Typeable Int 
Typeable Int8 
Typeable Int16 
Typeable Int32 
Typeable Int64 
Typeable Integer 
Typeable Ordering 
Typeable RealWorld 
Typeable Word 
Typeable Word8 
Typeable Word16 
Typeable Word32 
Typeable Word64 
Typeable Exp 
Typeable Match 
Typeable Clause 
Typeable Pat 
Typeable Type 
Typeable Dec 
Typeable Name 
Typeable FunDep 
Typeable Pred 
Typeable TyVarBndr 
Typeable () 
Typeable Handle 
Typeable Handle__ 
Typeable PatternMatchFail 
Typeable RecSelError 
Typeable RecConError 
Typeable RecUpdError 
Typeable NoMethodError 
Typeable NonTermination 
Typeable NestedAtomically 
Typeable BlockedIndefinitelyOnMVar 
Typeable BlockedIndefinitelyOnSTM 
Typeable Deadlock 
Typeable AssertionFailed 
Typeable AsyncException 
Typeable ArrayException 
Typeable ExitCode 
Typeable CChar 
Typeable CSChar 
Typeable CUChar 
Typeable CShort 
Typeable CUShort 
Typeable CInt 
Typeable CUInt 
Typeable CLong 
Typeable CULong 
Typeable CLLong 
Typeable CULLong 
Typeable CFloat 
Typeable CDouble 
Typeable CPtrdiff 
Typeable CSize 
Typeable CWchar 
Typeable CSigAtomic 
Typeable CClock 
Typeable CTime 
Typeable CUSeconds 
Typeable CSUSeconds 
Typeable CIntPtr 
Typeable CUIntPtr 
Typeable CIntMax 
Typeable CUIntMax 
Typeable IOException 
Typeable SomeException 
Typeable ErrorCall 
Typeable ArithException 
Typeable TypeRep 
Typeable TyCon 
Typeable NameFlavour 
Typeable NameSpace 
Typeable Info 
Typeable ClassInstance 
Typeable Fixity 
Typeable FixityDirection 
Typeable Lit 
Typeable Body 
Typeable Guard 
Typeable Stmt 
Typeable Range 
Typeable FamFlavour 
Typeable Foreign 
Typeable Callconv 
Typeable Safety 
Typeable Pragma 
Typeable InlineSpec 
Typeable Strict 
Typeable Con 
Typeable Kind 
Typeable ModName 
Typeable PkgName 
Typeable OccName 
Typeable Ann 
Typeable Verbosity 
Typeable CmdArgsPrivate 
Typeable ExceptionInt 
(Typeable1 s, Typeable a) => Typeable (s a)

One Typeable instance for all Typeable1 instances