Linked Questions

Popular Questions

How to parse a product type partially

Asked by At
data Config = Config {
    a :: Bool,
    b :: Type1,
    c :: Type2

pA :: Parser Bool

pB :: Parser Type1

pC :: Parser Type2

pConfig :: Parser Config
pConfig = Config <$> pA <*> pB <*> pC

opts :: ParserInfo Config
opts = info (pConfig <**> helper)
       (fullDesc <> progDesc "My CLI" <> header "CLI executable")

main :: IO()
main = do
       (Config a b c) <- execParser opts
-- Populate a default config using a b c values

Is it possible to parse a product type partially? Config is a product type with member a, b and c and assume this comes from a library, so I cannot redefine this. I only want to parse a and b without caring about c. But, since a "Parser Config" can only have a construction like below

Config <$> pA <*> pB <*> pC

due to being a product type, if I do not give a "pC" it errors out. How to correctly handle this scenario?

Related Questions