Options.Generic

-- 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)

$ stack build optparse-generic
$ stack runghc Example.hs -- --bar 2.5 --foo 1
Example {foo = 1, bar = 2.5}

$ stack runghc Example.hs -- --help
Test program

Usage: Example.hs --foo INT --bar DOUBLE

Available options:
  -h,--help                Show this help text

{-# 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)

$ 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

$ stack runghc Example.hs -- --foo 1 --bar 2.5
Example {foo = Helpful {unHelpful = 1}, bar = Helpful {unHelpful = 2.5}}

{-# LANGUAGE DataKinds          #-}
{-# LANGUAGE DeriveGeneric      #-}
{-# LANGUAGE FlexibleInstances  #-}  -- One more extension.
{-# LANGUAGE OverloadedStrings  #-}
{-# LANGUAGE StandaloneDeriving #-}  -- To derive Show
{-# LANGUAGE TypeOperators      #-}

import Options.Generic

data Example w = Example
    { foo :: w ::: Int    <?> "Documentation for the foo flag"
    , bar :: w ::: Double <?> "Documentation for the bar flag"
    } deriving (Generic)

instance ParseRecord (Example Wrapped)
deriving instance Show (Example Unwrapped)

main = do
    x <- unwrapRecord "Test program"
    print (x :: Example Unwrapped)

$ stack runghc Example.hs -- --foo 1 --bar 2.5
Example {foo = 1, bar = 2.5}

{-# LANGUAGE DataKinds         #-}
{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeOperators     #-}

import Options.Generic

data Example = Example
    { foo :: Int    <!> "1"
    , bar :: String <!> "hello"
    } deriving (Generic, Show)

instance ParseRecord Example

main = do
    x <- getRecord "Test program"
    print (x :: Example)

data Example = Example Int Double deriving (Generic, Show)

$ stack runghc Example.hs -- 1 2.5
Example 1 2.5

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)

$ 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}}

data Example
    = Create { name :: Text, duration :: Maybe Int }
    | Kill   { name :: Text }
    deriving (Generic, Show)

$ 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"}

{-# 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)

main = do
    x <- getRecord "Test program"
    print (x :: Int)

$ stack runghc Example.hs -- 2
2

    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’

{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE OverloadedStrings #-}

import Options.Generic

data Example = Example { foo :: Int, bar :: Double }
    deriving (Generic, Show)

modifiers :: Modifiers
modifiers = defaultModifiers
    { shortNameModifier = firstLetter
    }

instance ParseRecord Example where
    parseRecord = parseRecordWithModifiers modifiers

main = do
    x <- getRecord "Test program"
    print (x :: Example)