{-# LANGUAGE CPP #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeOperators #-}
-- | This library auto-generates command-line parsers for data types using
-- Haskell's built-in support for generic programming. The best way to
-- understand how this library works is to walk through a few examples.
--
-- For example, suppose that you want to parse a record with named fields like
-- this:
--
-- > -- Example.hs
-- >
-- > {-# LANGUAGE DeriveGeneric #-}
-- > {-# LANGUAGE OverloadedStrings #-}
-- >
-- > import Options.Generic
-- >
-- > data Example = Example { foo :: Int, bar :: Double }
-- > deriving (Generic, Show)
-- >
-- > instance ParseRecord Example
-- >
-- > main = do
-- > x <- getRecord "Test program"
-- > print (x :: Example)
--
-- Named fields translate to flags which you can provide in any order:
--
-- > $ stack build optparse-generic
-- > $ stack runghc Example.hs -- --bar 2.5 --foo 1
-- > Example {foo = 1, bar = 2.5}
--
-- This also auto-generates @--help@ output:
--
-- > $ stack runghc Example.hs -- --help
-- > Test program
-- >
-- > Usage: Example.hs --foo INT --bar DOUBLE
-- >
-- > Available options:
-- > -h,--help Show this help text
--
-- You can also add help descriptions to each field, like this:
--
-- > {-# LANGUAGE DataKinds #-}
-- > {-# LANGUAGE DeriveGeneric #-}
-- > {-# LANGUAGE OverloadedStrings #-}
-- > {-# LANGUAGE TypeOperators #-}
-- >
-- > import Options.Generic
-- >
-- > data Example = Example
-- > { foo :: Int <?> "Documentation for the foo flag"
-- > , bar :: Double <?> "Documentation for the bar flag"
-- > } deriving (Generic, Show)
-- >
-- > instance ParseRecord Example
-- >
-- > main = do
-- > x <- getRecord "Test program"
-- > print (x :: Example)
--
-- ... which produces the following @--help@ output:
--
-- > $ stack runghc Example.hs -- --help
-- > Test program
-- >
-- > Usage: Example.hs --foo INT --bar DOUBLE
-- >
-- > Available options:
-- > -h,--help Show this help text
-- > --foo INT Documentation for the foo flag
-- > --bar DOUBLE Documentation for the bar flag
--
-- However, any fields you document will be wrapped in the `Helpful`
-- constructor:
--
-- > $ stack runghc Example.hs -- --foo 1 --bar 2.5
-- > Example {foo = Helpful {unHelpful = 1}, bar = Helpful {unHelpful = 2.5}}
--
-- For the following examples I encourage you to test what @--help@ output they
-- generate.
--
-- This library will also do the right thing if the fields have no labels:
--
-- > data Example = Example Int Double deriving (Generic, Show)
--
-- Fields without labels translate into positional command-line arguments:
--
-- > $ stack runghc Example.hs -- 1 2.5
-- > Example 1 2.5
--
-- Certain types of fields are given special treatment, such as in this
-- example:
--
-- > data Example = Example
-- > { switch :: Bool
-- > , list :: [Int]
-- > , optional :: Maybe Int
-- > , first :: First Int
-- > , last :: Last Int
-- > , sum :: Sum Int
-- > , product :: Product Int
-- > } deriving (Generic, Show)
--
-- This gives the following behavior:
--
-- > $ stack runghc Example.hs --
-- > --switch
-- > --optional 1
-- > --list 1 --list 2
-- > --first 1 --first 2
-- > --last 1 --last 2
-- > --sum 1 --sum 2
-- > --product 1 --product 2
-- > Example {switch = True, list = [1,2], optional = Just 1, first = First
-- > {getFirst = Just 1}, last = Last {getLast = Just 2}, sum = Sum {getSum =
-- > 3}, product = Product {getProduct = 2}}
-- >
-- > $ stack runghc Example.hs
-- > Example {switch = False, list = [], optional = Nothing, first = First
-- > {getFirst = Nothing}, second = Last {getLast = Nothing}, sum = Sum {getSum
-- > = 0}, product = Product {getProduct = 1}}
--
-- If a datatype has multiple constructors:
--
-- > data Example
-- > = Create { name :: Text, duration :: Maybe Int }
-- > | Kill { name :: Text }
-- > deriving (Generic, Show)
--
-- ... then they will translate into subcommands named after each constructor:
--
-- > $ stack runghc Example.hs -- create --name foo --duration=60
-- > Create {name = "foo", duration = Just 60}
-- > $ stack runghc Example.hs -- kill --name foo
-- > Kill {name = "foo"}
--
-- This library also provides out-of-the-box support for many existing types,
-- like tuples and `Either`.
--
-- > {-# LANGUAGE DeriveGeneric #-}
-- > {-# LANGUAGE OverloadedStrings #-}
-- >
-- > import Options.Generic
-- >
-- > main = do
-- > x <- getRecord "Test program"
-- > print (x :: Either Double Int)
--
-- > $ stack runghc Example.hs -- left 1.0
-- > Left 1.0
-- > $ stack runghc Example.hs -- right 2
-- > Right 2
--
-- > main = do
-- > x <- getRecord "Test program"
-- > print (x :: (Double, Int))
--
-- > $ stack runghc Example.hs -- 1.0 2
-- > (1.0,2)
--
-- ... and you can also just parse a single value:
--
-- > main = do
-- > x <- getRecord "Test program"
-- > print (x :: Int)
--
-- > $ stack runghc Example.hs -- 2
-- > 2
--
-- However, there are some types that this library cannot generate sensible
-- command-line parsers for, such as:
--
-- * recursive types:
--
-- > data Example = Example { foo :: Example }
--
-- * records whose fields are other records
--
-- > data Outer = Outer { foo :: Inner } deriving (Show, Generic)
-- > data Inner = Inner { bar :: Int } deriving (Show, Generic)
--
-- * record fields with nested `Maybe`s or nested lists
--
-- > data Example = Example { foo :: Maybe (Maybe Int) }
-- > data Example = Example { foo :: [[Int]] }
--
-- If you try to auto-generate a parser for these types you will get an error at
-- compile time that will look something like this:
--
-- > No instance for (ParseFields TheTypeOfYourField)
-- > arising from a use of ‘Options.Generic.$gdmparseRecord’
-- > In the expression: Options.Generic.$gdmparseRecord
-- > In an equation for ‘parseRecord’:
-- > parseRecord = Options.Generic.$gdmparseRecord
-- > In the instance declaration for ‘ParseRecord TheTypeOfYourRecord’
module Options.Generic (
-- * Parsers
getRecord
, getRecordPure
, ParseRecord(..)
, ParseFields(..)
, ParseField(..)
, Only(..)
, getOnly
, Modifiers(..)
, parseRecordWithModifiers
, defaultModifiers
-- * Help
, type (<?>)(..)
-- * Re-exports
, Generic
, Text
, All(..)
, Any(..)
, First(..)
, Last(..)
, Sum(..)
, Product(..)
) where
import Control.Applicative
import Control.Monad.IO.Class (MonadIO(..))
import Data.Char (toLower, toUpper)
import Data.Monoid
import Data.List.NonEmpty (NonEmpty((:|)))
import Data.Proxy
import Data.Text (Text)
import Data.Typeable (Typeable)
import Data.Void (Void)
import Filesystem.Path (FilePath)
import GHC.Generics
import Prelude hiding (FilePath)
import Options.Applicative (Parser, ReadM)
import qualified Data.Text
import qualified Data.Text.Encoding
import qualified Data.Text.Lazy
import qualified Data.Text.Lazy.Encoding
import qualified Data.Time.Calendar
import qualified Data.Time.Format
import qualified Data.Typeable
import qualified Data.ByteString
import qualified Data.ByteString.Lazy
import qualified Filesystem.Path.CurrentOS as Filesystem
import qualified Options.Applicative as Options
import qualified Options.Applicative.Types as Options
import qualified Text.Read
#if MIN_VERSION_base(4,7,0)
import GHC.TypeLits
#else
import Data.Singletons.TypeLits
#endif
auto :: Read a => ReadM a
auto = do
s <- Options.readerAsk
case Text.Read.readMaybe s of
Just x -> return x
Nothing -> Options.readerAbort Options.ShowHelpText
{-| A class for all record fields that can be parsed from exactly one option or
argument on the command line
`parseField` has a default implementation for any type that implements
`Read` and `Typeable`. You can derive `Read` for many types and you can
derive `Typeable` for any type if you enable the @DeriveDataTypeable@
language extension
-}
class ParseField a where
parseField
:: Maybe Text
-- ^ Help message
-> Maybe Text
-- ^ Field label
-> Parser a
default parseField
:: (Typeable a, Read a)
=> Maybe Text
-- ^ Help message
-> Maybe Text
-- ^ Field label
-> Parser a
parseField h m = do
let metavar = map toUpper (show (Data.Typeable.typeOf (undefined :: a)))
case m of
Nothing -> do
let fs = Options.metavar metavar
<> maybe mempty (Options.help . Data.Text.unpack) h
Options.argument auto fs
Just name -> do
let fs = Options.metavar metavar
<> Options.long (Data.Text.unpack name)
<> maybe mempty (Options.help . Data.Text.unpack) h
Options.option auto fs
{-| The only reason for this method is to provide a special case for
handling `String`s. All other instances should just fall back on the
default implementation for `parseListOfField`
-}
parseListOfField
:: Maybe Text
-- ^ Help message
-> Maybe Text
-- ^ Field label
-> Parser [a]
parseListOfField h m = many (parseField h m)
instance ParseField Bool
instance ParseField Double
instance ParseField Float
instance ParseField Int
instance ParseField Integer
instance ParseField Ordering
instance ParseField ()
instance ParseField Void
instance ParseField String where
parseField = parseHelpfulString "STRING"
instance ParseField Char where
parseField h m = do
let metavar = "CHAR"
let readM = do
s <- Options.readerAsk
case s of
[c] -> return c
_ -> Options.readerAbort Options.ShowHelpText
case m of
Nothing -> do
let fs = Options.metavar metavar
<> maybe mempty (Options.help . Data.Text.unpack) h
Options.argument readM fs
Just name -> do
let fs = Options.metavar metavar
<> Options.long (Data.Text.unpack name)
<> maybe mempty (Options.help . Data.Text.unpack) h
Options.option readM fs
parseListOfField = parseHelpfulString "STRING"
instance ParseField Any where
parseField h m = Any <$> parseField h m
instance ParseField All where
parseField h m = All <$> parseField h m
parseHelpfulString :: String -> Maybe Text -> Maybe Text -> Parser String
parseHelpfulString metavar h m =
case m of
Nothing -> do
let fs = Options.metavar metavar
<> maybe mempty (Options.help . Data.Text.unpack) h
Options.argument Options.str fs
Just name -> do
let fs = Options.metavar metavar
<> Options.long (Data.Text.unpack name)
<> maybe mempty (Options.help . Data.Text.unpack) h
Options.option Options.str fs
instance ParseField Data.Text.Text where
parseField h m = Data.Text.pack <$> parseHelpfulString "TEXT" h m
instance ParseField Data.ByteString.ByteString where
parseField h m = fmap Data.Text.Encoding.encodeUtf8 (parseField h m)
instance ParseField Data.Text.Lazy.Text where
parseField h m = Data.Text.Lazy.pack <$> parseHelpfulString "TEXT" h m
instance ParseField Data.ByteString.Lazy.ByteString where
parseField h m = fmap Data.Text.Lazy.Encoding.encodeUtf8 (parseField h m)
instance ParseField FilePath where
parseField h m = Filesystem.decodeString <$> parseHelpfulString "FILEPATH" h m
instance ParseField Data.Time.Calendar.Day where
parseField h m = do
let metavar = "YYYY-MM-DD"
case m of
Nothing -> do
let fs = Options.metavar metavar
<> maybe mempty (Options.help . Data.Text.unpack) h
Options.argument iso8601Day fs
Just name -> do
let fs = Options.metavar metavar
<> Options.long (Data.Text.unpack name)
<> maybe mempty (Options.help . Data.Text.unpack) h
Options.option iso8601Day fs
where
iso8601Day = Options.eitherReader
$ runReadS . Data.Time.Format.readSTime
False
Data.Time.Format.defaultTimeLocale
"%F"
runReadS [(day, "")] = Right day
runReadS _ = Left "expected YYYY-MM-DD"
{-| A class for all types that can be parsed from zero or more arguments/options
on the command line
`parseFields` has a default implementation for any type that implements
`ParseField`
-}
class ParseRecord a => ParseFields a where
parseFields
:: Maybe Text
-- ^ Help message
-> Maybe Text
-- ^ Field label
-> Parser a
default parseFields :: ParseField a => Maybe Text -> Maybe Text -> Parser a
parseFields = parseField
instance ParseFields Char
instance ParseFields Double
instance ParseFields Float
instance ParseFields Int
instance ParseFields Integer
instance ParseFields Ordering
instance ParseFields Void
instance ParseFields Data.ByteString.ByteString
instance ParseFields Data.ByteString.Lazy.ByteString
instance ParseFields Data.Text.Text
instance ParseFields Data.Text.Lazy.Text
instance ParseFields FilePath
instance ParseFields Data.Time.Calendar.Day
instance ParseFields Bool where
parseFields h m =
case m of
Nothing -> do
let fs = Options.metavar "BOOL"
<> maybe mempty (Options.help . Data.Text.unpack) h
Options.argument auto fs
Just name -> do
Options.switch $
Options.long (Data.Text.unpack name)
<> maybe mempty (Options.help . Data.Text.unpack) h
instance ParseFields () where
parseFields _ _ = pure ()
instance ParseFields Any where
parseFields h m = (fmap mconcat . many . fmap Any) (parseField h m)
instance ParseFields All where
parseFields h m = (fmap mconcat . many . fmap All) (parseField h m)
instance ParseField a => ParseFields (Maybe a) where
parseFields h m = optional (parseField h m)
instance ParseField a => ParseFields (First a) where
parseFields h m = (fmap mconcat . many . fmap (First . Just)) (parseField h m)
instance ParseField a => ParseFields (Last a) where
parseFields h m = (fmap mconcat . many . fmap (Last . Just)) (parseField h m)
instance (Num a, ParseField a) => ParseFields (Sum a) where
parseFields h m = (fmap mconcat . many . fmap Sum) (parseField h m)
instance (Num a, ParseField a) => ParseFields (Product a) where
parseFields h m = (fmap mconcat . many . fmap Product) (parseField h m)
instance ParseField a => ParseFields [a] where
parseFields = parseListOfField
instance ParseField a => ParseFields (NonEmpty a) where
parseFields h m = (:|) <$> parseField h m <*> parseListOfField h m
{-| Use this to annotate a field with a type-level string (i.e. a `Symbol`)
representing the help description for that field:
> data Example = Example
> { foo :: Int <?> "Documentation for the foo flag"
> , bar :: Double <?> "Documentation for the bar flag"
> } deriving (Generic, Show)
-}
newtype (<?>) (field :: *) (help :: Symbol) = Helpful { unHelpful :: field } deriving (Generic, Show)
instance (ParseField a, KnownSymbol h) => ParseField (a <?> h) where
parseField _ m = Helpful <$>
parseField ((Just . Data.Text.pack .symbolVal) (Proxy :: Proxy h)) m
instance (ParseFields a, KnownSymbol h) => ParseFields (a <?> h) where
parseFields _ m = Helpful <$>
parseFields ((Just . Data.Text.pack .symbolVal) (Proxy :: Proxy h)) m
instance (ParseFields a, KnownSymbol h) => ParseRecord (a <?> h)
{-| A 1-tuple, used solely to translate `ParseFields` instances into
`ParseRecord` instances
-}
newtype Only a = Only a deriving (Generic, Show)
{-| This is a convenience function that you can use if you want to create a
`ParseRecord` instance that just defers to the `ParseFields` instance for
the same type:
> instance ParseRecord MyType where
> parseRecord = fmap getOnly parseRecord
-}
getOnly :: Only a -> a
getOnly (Only x) = x
{-| A class for types that can be parsed from the command line
This class has a default implementation for any type that implements
`Generic` and you can derive `Generic` for many types by enabling the
@DeriveGeneric@ language extension
You can also use `getOnly` to create a `ParseRecord` instance from a
`ParseFields` instance:
> instance ParseRecord MyType where
> parseRecord = fmap getOnly parseRecord
-}
class ParseRecord a where
parseRecord :: Parser a
default parseRecord :: (Generic a, GenericParseRecord (Rep a)) => Parser a
parseRecord = fmap GHC.Generics.to (genericParseRecord defaultModifiers)
instance ParseFields a => ParseRecord (Only a)
instance ParseRecord Char where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Double where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Float where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Int where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Ordering
instance ParseRecord Void
instance ParseRecord ()
instance ParseRecord Bool where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Integer where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Data.Text.Text where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Data.Text.Lazy.Text where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Any where
parseRecord = fmap getOnly parseRecord
instance ParseRecord All where
parseRecord = fmap getOnly parseRecord
instance ParseRecord FilePath where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Data.ByteString.ByteString where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Data.ByteString.Lazy.ByteString where
parseRecord = fmap getOnly parseRecord
instance ParseRecord Data.Time.Calendar.Day where
parseRecord = fmap getOnly parseRecord
instance ParseField a => ParseRecord (Maybe a) where
parseRecord = fmap getOnly parseRecord
instance ParseField a => ParseRecord (First a) where
parseRecord = fmap getOnly parseRecord
instance ParseField a => ParseRecord (Last a) where
parseRecord = fmap getOnly parseRecord
instance (Num a, ParseField a) => ParseRecord (Sum a) where
parseRecord = fmap getOnly parseRecord
instance (Num a, ParseField a) => ParseRecord (Product a) where
parseRecord = fmap getOnly parseRecord
instance ParseField a => ParseRecord [a] where
parseRecord = fmap getOnly parseRecord
instance ParseField a => ParseRecord (NonEmpty a) where
parseRecord = fmap getOnly parseRecord
instance (ParseFields a, ParseFields b) => ParseRecord (a, b)
instance (ParseFields a, ParseFields b, ParseFields c) => ParseRecord (a, b, c)
instance (ParseFields a, ParseFields b, ParseFields c, ParseFields d) => ParseRecord (a, b, c, d)
instance (ParseFields a, ParseFields b, ParseFields c, ParseFields d, ParseFields e) => ParseRecord (a, b, c, d, e)
instance (ParseFields a, ParseFields b, ParseFields c, ParseFields d, ParseFields e, ParseFields f) => ParseRecord (a, b, c, d, e, f)
instance (ParseFields a, ParseFields b, ParseFields c, ParseFields d, ParseFields e, ParseFields f, ParseFields g) => ParseRecord (a, b, c, d, e, f, g)
instance (ParseFields a, ParseFields b) => ParseRecord (Either a b)
data Modifiers = Modifiers
{ fieldNameModifier :: String -> String
, constructorNameModifier :: String -> String
}
defaultModifiers :: Modifiers
defaultModifiers = Modifiers id (map toLower)
class GenericParseRecord f where
genericParseRecord :: Modifiers -> Parser (f p)
instance GenericParseRecord U1 where
genericParseRecord _ = pure U1
-- See: [NOTE - Sums]
instance GenericParseRecord f => GenericParseRecord (M1 C c f) where
genericParseRecord = fmap M1 . genericParseRecord
-- See: [NOTE - Sums]
instance (GenericParseRecord (f :+: g), GenericParseRecord (h :+: i)) => GenericParseRecord ((f :+: g) :+: (h :+: i)) where
genericParseRecord mods = do
fmap L1 (genericParseRecord mods) <|> fmap R1 (genericParseRecord mods)
-- See: [NOTE - Sums]
instance (Constructor c, GenericParseRecord f, GenericParseRecord (g :+: h)) => GenericParseRecord (M1 C c f :+: (g :+: h)) where
genericParseRecord mods@Modifiers{..} = do
let m :: M1 i c f a
m = undefined
let name = constructorNameModifier (conName m)
let info = Options.info (Options.helper <*> (genericParseRecord mods)) mempty
let subparserFields =
Options.command name info
<> Options.metavar name
let parser = Options.subparser subparserFields
fmap (L1 . M1) parser <|> fmap R1 (genericParseRecord mods)
-- See: [NOTE - Sums]
instance (Constructor c, GenericParseRecord (f :+: g), GenericParseRecord h) => GenericParseRecord ((f :+: g) :+: M1 C c h) where
genericParseRecord mods@Modifiers{..} = do
let m :: M1 i c h a
m = undefined
let name = constructorNameModifier (conName m)
let info = Options.info (Options.helper <*> (genericParseRecord mods)) mempty
let subparserFields =
Options.command name info
<> Options.metavar name
let parser = Options.subparser subparserFields
fmap L1 (genericParseRecord mods) <|> fmap (R1 . M1) parser
-- See: [NOTE - Sums]
instance (Constructor c1, Constructor c2, GenericParseRecord f1, GenericParseRecord f2) => GenericParseRecord (M1 C c1 f1 :+: M1 C c2 f2) where
genericParseRecord mods@Modifiers{..} = do
let m1 :: M1 i c1 f a
m1 = undefined
let m2 :: M1 i c2 g a
m2 = undefined
let name1 = constructorNameModifier (conName m1)
let name2 = constructorNameModifier (conName m2)
let info1 = Options.info (Options.helper <*> (genericParseRecord mods)) mempty
let info2 = Options.info (Options.helper <*> (genericParseRecord mods)) mempty
let subparserFields1 =
Options.command name1 info1
<> Options.metavar name1
let subparserFields2 =
Options.command name2 info2
<> Options.metavar name2
let parser1 = Options.subparser subparserFields1
let parser2 = Options.subparser subparserFields2
fmap (L1 . M1) parser1 <|> fmap (R1 . M1) parser2
instance (GenericParseRecord f, GenericParseRecord g) => GenericParseRecord (f :*: g) where
genericParseRecord mods = liftA2 (:*:) (genericParseRecord mods) (genericParseRecord mods)
instance GenericParseRecord V1 where
genericParseRecord _ = empty
instance (Selector s, ParseFields a) => GenericParseRecord (M1 S s (K1 i a)) where
genericParseRecord Modifiers{..} = do
let m :: M1 i s f a
m = undefined
let label = case (selName m) of
"" -> Nothing
name -> Just (Data.Text.pack (fieldNameModifier name))
fmap (M1 . K1) (parseFields Nothing label)
{- [NOTE - Sums]
You might wonder why the `GenericParseRecord` instances for `(:+:)` are so
complicated. A much simpler approach would be something like this:
> instance (GenericParseRecord f, GenericParseRecord g) => GenericParseRecord (f :+: g) where
> genericParseRecord = fmap L1 genericParseRecord <|> fmap R1 genericParseRecord
>
> instance (Constructor c, GenericParseRecord f) => GenericParseRecord (M1 C c f) where
> genericParseRecord = do
> let m :: M1 i c f a
> m = undefined
>
> let name = map toLower (conName m)
>
> let info = Options.info genericParseRecord mempty
>
> let subparserFields =
> Options.command n info
> <> Options.metavar n
>
> fmap M1 (Options.subparser subparserFields)
The reason for the extra complication is so that datatypes with just one
constructor don't have subcommands. That way, if a user defines a data
type like:
> data Example = Example { foo :: Double } deriving (Generic)
>
> instance ParseRecord Example
.. then the command line will only read in the @--foo@ flag and won't
expect a gratuitous @example@ subcommand:
> ./example --foo 2
However, if a user defines a data type with two constructors then the
subcommand support will kick in.
Some other alternatives that I considered and rejected:
* Alternative #1: Constructors prefixed with something like @Command_@ are
turned into sub-commands named after the constructor with the prefix
stripped. If the prefix is not present then they don't get a subcommand.
I rejected this approach for several reasons:
* It's ugly
* It's error-prone (consider the case: @data T = C1 Int | C2 Int@, which
would never successfully parse @C2@). Subcommands should be mandatory
for types with multiple constructors
* It doesn't work "out-of-the-box" for most types in the Haskell
ecosystem which were not written with this library in mind
* Alternative #2: Any constructor named some reserved name (like @Only@)
would not generate a sub-command.
I rejected this approach for a couple of reasons:
* Too surprising. The user would never know or guess about this
behavior without reading the documentation.
* Doesn't work "out-of-the-box" for single-constructor types in the
Haskell ecosystem (like `(a, b)`, for example)
-}
instance GenericParseRecord f => GenericParseRecord (M1 D c f) where
genericParseRecord mods = fmap M1 (Options.helper <*> genericParseRecord mods)
parseRecordWithModifiers :: (Generic a, GenericParseRecord (Rep a)) => Modifiers -> Parser a
parseRecordWithModifiers mods = fmap GHC.Generics.to (genericParseRecord mods)
-- | Marshal any value that implements `ParseRecord` from the command line
getRecord
:: (MonadIO io, ParseRecord a)
=> Text
-- ^ Program description
-> io a
getRecord desc = liftIO (Options.customExecParser prefs info)
where
prefs = Options.defaultPrefs
{ Options.prefMultiSuffix = "..."
}
header = Options.header (Data.Text.unpack desc)
info = Options.info parseRecord header
{-| Pure version of `getRecord`
>>> :set -XOverloadedStrings
>>> getRecordPure ["1"] :: Maybe Int
Just 1
>>> getRecordPure ["1", "2"] :: Maybe [Int]
Just [1,2]
>>> getRecordPure ["Foo"] :: Maybe Int
Nothing
-}
getRecordPure
:: ParseRecord a
=> [Text]
-- ^ Command-line arguments
-> Maybe a
getRecordPure args = do
let prefs = Options.ParserPrefs
{ prefMultiSuffix = "..."
, prefDisambiguate = False
, prefShowHelpOnError = False
, prefBacktrack = True
, prefColumns = 80
#if MIN_VERSION_optparse_applicative(0,13,0)
, prefShowHelpOnEmpty = False
#else
#endif
}
let header = Options.header ""
let info = Options.info parseRecord header
let args' = map Data.Text.unpack args
Options.getParseResult (Options.execParserPure prefs info args')