有例子:https://github.com/pcapriotti/optparse-applicative/blob/master/tests/Examples/Cabal.hs#L46-L62
parser :: Parser Args
parser = runA $ proc () -> do
opts <- asA commonOpts -< ()
cmds <- (asA . hsubparser)
( command "install"
(info installParser
(progDesc "Installs a list of packages"))
<> command "update"
(info updateParser
(progDesc "Updates list of known packages"))
<> command "configure"
(info configureParser
(progDesc "Prepare to build the package"))
<> command "build"
(info buildParser
(progDesc "Make this package ready for installation")) ) -< ()
A version >>> A helper -< Args opts cmds
...
pinfo :: ParserInfo Args
pinfo = info parser
( progDesc "An example modelled on cabal" )
main :: IO ()
main = do
r <- execParser pinfo
print r
因此,默认情况下,当我不使用参数时,它会显示使用信息。我想使用没有参数的情况,还有一个[自定义参数](使用自定义的一个我收到错误:Invalid argument 'regreg'
)
我如何在这里处理空和自定义参数?
答案 0 :(得分:2)
A
不是ArrowPlus。我不确定它是否可以(假设f
是Alternative
),但是现在你必须使用Alternative
语法:
subparser (command "foo" ... ...) <|> pure DefaultCommand