cmdargs-0.10.6: Command line argument processing

Safe HaskellNone




This module captures annotations on a value, and builds a Capture value. This module has two ways of writing annotations:

Impure: The impure method of writing annotations is susceptible to over-optimisation by GHC - sometimes {-# OPTIONS_GHC -fno-cse #-} will be required.

Pure: The pure method is more verbose, and lacks some type safety.

As an example of the two styles:

 data Foo = Foo {foo :: Int, bar :: Int}
 impure = capture $ Foo {foo = 12, bar = many [1 &= "inner", 2]} &= "top"
 pure = capture_ $ record Foo{} [foo := 12, bar :=+ [atom 1 += "inner", atom 2]] += "top"

Both evaluate to:

 Capture (Ann "top") (Ctor (Foo 12 1) [Value 12, Many [Ann "inner" (Value 1), Value 2]]


Capture framework

data Capture ann Source

The result of capturing some annotations.


Many [Capture ann]

Many values collapsed (many or many_)

Ann ann (Capture ann)

An annotation attached to a value (&= or +=)

Value Any

A value (just a value, or atom)

Missing Any

A missing field (a RecConError exception, or missing from record)

Ctor Any [Capture ann]

A constructor (a constructor, or record)


Functor Capture 
Show ann => Show (Capture ann) 

data Any Source

Any value, with a Data dictionary.


forall a . Data a => Any a 


fromCapture :: Capture ann -> AnySource

Return the value inside a capture.

defaultMissing :: Capture ann -> Capture annSource

Remove all Missing values by using any previous instances as default values


capture :: (Data val, Data ann) => val -> Capture annSource

Capture a value. Note that if the value is evaluated more than once the result may be different, i.e.

 capture x /= capture x

many :: Data val => [val] -> valSource

Collapse multiple values in to one.

(&=) :: (Data val, Data ann) => val -> ann -> valSource

Add an annotation to a value.

It is recommended that anyone making use of this function redefine it with a more restrictive type signature to control the type of the annotation (the second argument). Any redefinitions of this function should add an INLINE pragma, to reduce the chance of incorrect optimisations.


capture_ :: Show a => Annotate a -> Capture aSource

Capture the annotations from an annotated value.

many_ :: [Annotate a] -> Annotate aSource

Collapse many annotated values in to one.

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

Add an annotation to a value.

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

Lift a pure value to an annotation.

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.

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.

forall c f . (Data c, Data f) => (c -> f) :=+ [Annotate ann]

Add annotations to a field.