System.Console.CmdArgs.Annotate

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

The result of capturing some annotations.

Constructors

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)

Instances

Functor Capture

Show ann => Show (Capture ann)

data Any

Any value, with a Data dictionary.

Constructors

forall a . Data a => Any a

Instances

Show Any

fromCapture :: Capture ann -> Any

Return the value inside a capture.

defaultMissing :: Capture ann -> Capture ann

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

Impure

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

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] -> val

Collapse multiple values in to one.

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

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.

Pure

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

Capture the annotations from an annotated value.

many_ :: [Annotate a] -> Annotate a

Collapse many annotated values in to one.

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

Add an annotation to a value.

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

Lift a pure value to an annotation.

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

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

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

Constructors

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.

Instances

Typeable1 Annotate