Safe Haskell	None
Language	Haskell2010
Extensions	Cpp ScopedTypeVariables OverloadedStrings DisambiguateRecordFields RecordWildCards TypeSynonymInstances FlexibleContexts FlexibleInstances UnicodeSyntax RankNTypes ExplicitForAll

Configuration.Utils

Contents

Program Configuration
Running an Configured Application
Applicative Option Parsing with Default Values
Parsing of Configuration Files with Default Values
Misc Utils
Configuration of Optional Values
Reexports

Description

This module provides a collection of utils on top of the packages optparse-applicative, aeson, and yaml, for configuring libraries and applications in a composable way.

The main feature is the integration of command line option parsing and configuration files.

The purpose is to make management of configurations easy by providing an idiomatic style of defining and deploying configurations.

For each data type that is used as a configuration type the following must be provided:

a default value,
a FromJSON instance that yields a function that takes a value and updates that value with the parsed values,
a ToJSON instance, and
an options parser that yields a function that takes a value and updates that value with the values provided as command line options.

The module provides operators and functions that make the implmentation of these entities easy for the common case that the configurations are encoded mainly as nested records.

The operators assume that lenses for the configuration record types are provided.

An complete usage example can be found in the file example/Example.hs of the cabal package.

Synopsis

Program Configuration

data ProgramInfo α Source

programInfo :: String -> MParser α -> α -> ProgramInfo α Source

Smart constructor for ProgramInfo.

piHelpHeader and piHelpFooter are set to Nothing.

piDescription :: Lens' (ProgramInfo α) String Source

Program Description

piHelpHeader :: Lens' (ProgramInfo α) (Maybe String) Source

Help header

piHelpFooter :: Lens' (ProgramInfo α) (Maybe String) Source

Help footer

piOptionParser :: Lens' (ProgramInfo α) (MParser α) Source

options parser for configuration (TODO consider using a typeclass for this)

piDefaultConfiguration :: Lens' (ProgramInfo α) α Source

default configuration

piOptionParserAndDefaultConfiguration :: Lens (ProgramInfo α) (ProgramInfo β) (MParser α, α) (MParser β, β) Source

Lens for simultaneous query and update of piOptionParser and piDefaultConfiguration. This supports to change the type of ProgramInfo with over and set.

Running an Configured Application

runWithConfiguration :: (FromJSON (α -> α), ToJSON α) => ProgramInfo α -> (α -> IO ()) -> IO () Source

Run an IO action with a configuration that is obtained by updating the given default configuration the values defined via command line arguments.

In addition to the options defined by the given options parser the following options are recognized:

--config-file, -c: Parse the given file path as a (partial) configuration in YAML format.
--print-config, -p: Print the final parsed configuration to standard out and exit.
--help, -h: Print a help message and exit.

type PkgInfo = (String, String, String, String) Source

Information about the cabal package. The format is:

(info message, detailed info message, version string, license text)

See the documentation of Configuration.Utils.Setup for a way how to generate this information automatically from the package description during the build process.

runWithPkgInfoConfiguration :: (FromJSON (α -> α), ToJSON α) => ProgramInfo α -> PkgInfo -> (α -> IO ()) -> IO () Source

Run an IO action with a configuration that is obtained by updating the given default configuration the values defined via command line arguments.

In addition to the options defined by the given options parser the following options are recognized:

--config-file, -c: Parse the given file path as a (partial) configuration in YAML format.
--print-config, -p: Print the final parsed configuration to standard out and exit.
--help, -h: Print a help message and exit.
--version, -v: Print the version of the application and exit.
--info, -i: Print a short info message for the application and exit.
--long-inf: Print a detailed info message for the application and exit.
--license: Print the text of the lincense of the application and exit.

Applicative Option Parsing with Default Values

type MParser α = Parser (α -> α) Source

Type of option parsers that yield a modification function.

(.::) :: (Alternative φ, Applicative φ) => Lens' α β -> φ β -> φ (α -> α) infixr 5 Source

An operator for applying a setter to an option parser that yields a value.

Example usage:

data Auth = Auth
    { _user ∷ !String
    , _pwd ∷ !String
    }

user ∷ Functor φ ⇒ (String → φ String) → Auth → φ Auth
user f s = (\u → s { _user = u }) <$> f (_user s)

pwd ∷ Functor φ ⇒ (String → φ String) → Auth → φ Auth
pwd f s = (\p → s { _pwd = p }) <$> f (_pwd s)

-- or with lenses and TemplateHaskell just:
-- $(makeLenses ''Auth)

pAuth ∷ MParser Auth
pAuth = id
   <$< user .:: strOption
       × long "user"
       ⊕ short 'u'
       ⊕ help "user name"
   <*< pwd .:: strOption
       × long "pwd"
       ⊕ help "password for user"

(%::) :: (Alternative φ, Applicative φ) => Lens' α β -> φ (β -> β) -> φ (α -> α) infixr 5 Source

An operator for applying a setter to an option parser that yields a modification function.

Example usage:

data HttpURL = HttpURL
    { _auth ∷ !Auth
    , _domain ∷ !String
    }

auth ∷ Functor φ ⇒ (Auth → φ Auth) → HttpURL → φ HttpURL
auth f s = (\u → s { _auth = u }) <$> f (_auth s)

domain ∷ Functor φ ⇒ (String → φ String) → HttpURL → φ HttpURL
domain f s = (\u → s { _domain = u }) <$> f (_domain s)

path ∷ Functor φ ⇒ (String → φ String) → HttpURL → φ HttpURL
path f s = (\u → s { _path = u }) <$> f (_path s)

-- or with lenses and TemplateHaskell just:
-- $(makeLenses ''HttpURL)

pHttpURL ∷ MParser HttpURL
pHttpURL = id
    <$< auth %:: pAuth
    <*< domain .:: strOption
        × long "domain"
        ⊕ short 'd'
        ⊕ help "HTTP domain"

Parsing of Configuration Files with Default Values

setProperty Source

Arguments

:: Lens' α β	a lens into the target that is updated by the parser
-> Text	the JSON property name
-> (Value -> Parser β)	the JSON `Value` parser that is used to parse the value of the property
-> Object	the parsed JSON `Value` `Object`
-> Parser (α -> α)

A JSON Value parser for a property of a given Object that updates a setter with the parsed value.

data Auth = Auth
    { _userId ∷ !Int
    , _pwd ∷ !String
    }

userId ∷ Functor φ ⇒ (Int → φ Int) → Auth → φ Auth
userId f s = (\u → s { _userId = u }) <$> f (_userId s)

pwd ∷ Functor φ ⇒ (String → φ String) → Auth → φ Auth
pwd f s = (\p → s { _pwd = p }) <$> f (_pwd s)

-- or with lenses and TemplateHaskell just:
-- $(makeLenses ''Auth)

instance FromJSON (Auth → Auth) where
    parseJSON = withObject "Auth" $ \o → id
        <$< setProperty user "user" p o
        <*< setProperty pwd "pwd" parseJSON o
      where
        p = withText "user" $ \case
            "alice" → pure (0 ∷ Int)
            "bob" → pure 1
            e → fail $ "unrecognized user " ⊕ e

(..:) :: FromJSON β => Lens' α β -> Text -> Object -> Parser (α -> α) infix 6 Source

A variant of the setProperty that uses the default parseJSON method from the FromJSON instance to parse the value of the property. Its usage pattern mimics the usage pattern of the .: operator from the aeson library.

data Auth = Auth
    { _user ∷ !String
    , _pwd ∷ !String
    }

user ∷ Functor φ ⇒ (String → φ String) → Auth → φ Auth
user f s = (\u → s { _user = u }) <$> f (_user s)

pwd ∷ Functor φ ⇒ (String → φ String) → Auth → φ Auth
pwd f s = (\p → s { _pwd = p }) <$> f (_pwd s)

-- or with lenses and TemplateHaskell just:
-- $(makeLenses ''Auth)

instance FromJSON (Auth → Auth) where
    parseJSON = withObject "Auth" $ \o → id
        <$< user ..: "user" × o
        <*< pwd ..: "pwd" × o

(%.:) :: FromJSON (β -> β) => Lens' α β -> Text -> Object -> Parser (α -> α) infix 6 Source

A variant of the aeson operator .: that creates a parser that modifies a setter with a parsed function.

data HttpURL = HttpURL
    { _auth ∷ !Auth
    , _domain ∷ !String
    }

auth ∷ Functor φ ⇒ (Auth → φ Auth) → HttpURL → φ HttpURL
auth f s = (\u → s { _auth = u }) <$> f (_auth s)

domain ∷ Functor φ ⇒ (String → φ String) → HttpURL → φ HttpURL
domain f s = (\u → s { _domain = u }) <$> f (_domain s)

path ∷ Functor φ ⇒ (String → φ String) → HttpURL → φ HttpURL
path f s = (\u → s { _path = u }) <$> f (_path s)

-- or with lenses and TemplateHaskell just:
-- $(makeLenses ''HttpURL)

instance FromJSON (HttpURL → HttpURL) where
    parseJSON = withObject "HttpURL" $ \o → id
        <$< auth %.: "auth" × o
        <*< domain ..: "domain" × o

Misc Utils

(%) :: (α -> β) -> α -> β infixr 5 Source

This operator is an alternative for $ with a higher precedence which makes it suitable for usage within Applicative style funtors without the need to add parenthesis.

(×) :: (α -> β) -> α -> β infixr 5 Source

This operator is a UTF-8 version of % which is an alternative for $ with a higher precedence which makes it suitable for usage within Applicative style funtors without the need to add parenthesis.

The hex value of the UTF-8 character × is 0x00d7.

In VIM type: Ctrl-V u 00d7

You may also define a key binding by adding something like the following line to your vim configuration file:

iabbrev <buffer> >< ×

(<*<) :: Applicative φ => φ (β -> γ) -> φ (α -> β) -> φ (α -> γ) infixr 4 Source

Functional composition for applicative functors.

(>*>) :: Applicative φ => φ (α -> β) -> φ (β -> γ) -> φ (α -> γ) infixr 4 Source

Functional composition for applicative functors with its arguments flipped.

(<$<) :: Functor φ => (β -> γ) -> φ (α -> β) -> φ (α -> γ) infixr 4 Source

Applicative functional composition between a pure function and an applicative function.

(>$>) :: Functor φ => φ (α -> β) -> (β -> γ) -> φ (α -> γ) infixr 4 Source

Applicative functional composition between a pure function and an applicative function with its arguments flipped.

(<.>) :: Applicative φ => φ (β -> γ) -> φ (α -> β) -> φ (α -> γ) infixr 4 Source

Deprecated: use <*< instead

Functional composition for applicative functors.

This is a rather popular operator. Due to conflicts (for instance with the lens package) it may have to be imported qualified.

(⊙) :: Applicative φ => φ (β -> γ) -> φ (α -> β) -> φ (α -> γ) infixr 4 Source

Deprecated: use <*< instead

For people who like nicely aligned code and do not mind messing with editor key-maps: here a version of <.> that uses a unicode symbol

The hex value of the UTF-8 character ⊙ is 0x2299.

A convenient VIM key-map is:

iabbrev <buffer> ../ ⊙

dropAndUncaml :: Int -> String -> String Source

type Lens' σ α = Lens σ σ α α Source

This is the same type as the type from the lens library with the same name.

type Lens σ τ α β = Functor φ => (α -> φ β) -> σ -> φ τ Source

This is the same type as the type from the lens library with the same name.

Configuration of Optional Values

Optional configuration values are supposed to be encoded by wrapping the respective type with Maybe.

For simple values the standard FromJSON instance from the aeson package can be used with the along with the ..: operator.

When defining command line option parsers with .:: and %:: all options are optional. When an option is not present on the command line the default value is used. For Maybe values it is therefore enough to wrap the parsed value into Just.

data LogConfig = LogConfig
   { _logLevel ∷ !Int
   , _logFile ∷ !(Maybe String)
   }

$(makeLenses ''LogConfig)

defaultLogConfig ∷ LogConfig
defaultLogConfig = LogConfig
    { _logLevel = 1
    , _logFile = Nothing
    }

instance FromJSON (LogConfig → LogConfig) where
    parseJSON = withObject "LogConfig" $ \o → id
        <$< logLevel ..: "LogLevel" % o
        <*< logFile ..: "LogConfig" % o

instance ToJSON LogConfig where
    toJSON config = object
        [ "LogLevel" .= _logLevel config
        , "LogConfig" .= _logFile config
        ]

pLogConfig ∷ MParser LogConfig
pLogConfig = id
#if MIN_VERSION_optparse-applicative(0,10,0)
    <$< logLevel .:: option auto
#else
    <$< logLevel .:: option
#endif
        % long "log-level"
        % metavar "INTEGER"
        % help "log level"
    <*< logFile .:: fmap Just % strOption
        % long "log-file"
        % metavar "FILENAME"
        % help "log file name"

For product-type (record) Maybe values the following orphan FromJSON instance is provided:

instance (FromJSON (a → a), FromJSON a) ⇒ FromJSON (Maybe a → Maybe a)
    parseJSON Null = pure (const Nothing)
    parseJSON v = f <$> parseJSON v <*> parseJSON v
      where
        f g _ Nothing = Just g
        f _ g (Just x) = Just (g x)

(Using an orphan instance is generally problematic but convenient in this case. It's unlikely that an instance for this type is needed elsewhere. If this is an issue for you, please let me know. In that case we can define a new type for optional configuration values.)

The semantics are as follows:

If the parsed configuration value is Null the result is Nothing.
If the parsed configuration value is not Null then the result is an update function that
- updates the given default value if this value is Just x or
- is a constant function that returns the value that is parsed from the configuration using the FromJSON instance for the configuration type.

Note, that this instance requires an FromJSON instance for the configuration type itself as well as a FromJSON instance for the update function of the configuration type. The former can be defined by means of the latter as follows:

instance FromJSON MyType where
    parseJSON v = parseJSON v <*> pure defaultMyType

This instance will cause the usage of defaultMyType as default value if the default value that is given to the configuration parser is Nothing and the parsed configuration is not Null.

Reexports

module Data.Aeson

module Options.Applicative