[Haskell-cafe] Re: how to pipe in pure input with HSH? (Would be helpful for sending emails via sendmail/mailx via HSH interface)

[John Goerzen]

Thomas Hartman wrote:
> {-
> I am trying to figure out a way to send email using HSH and I'm stumped.
> 
> The problem is that there is no ShellCommand instance for a pure
> vanilla string, which can be piped into another ShellCommand. There is
> a ShellCommand String instance, but the string is a command to be
> executed.

Hi Thomas,

See echo and echoBS here:

http://hackage.haskell.org/packages/archive/HSH/1.2.6/doc/html/HSH-ShellEquivs.html#v%3Aecho

-- John

> 
> I defined PureInput wrapper around String in an attempt to get this
> working, but I'm stumped defining
> an fdInvoke method for it.
> 
> class (Show a) => ShellCommand a where
>   fdInvoke ::
>     a
>     -> System.Posix.Types.Fd
>     -> System.Posix.Types.Fd
>     -> [System.Posix.Types.Fd]
>     -> IO ()
>     -> IO [InvokeResult]
> 
> Can someone help out? Below is a stub.
> 
> Thomas.
> -}
> 
> import HSH
> 
> newtype PureInput = PureInput { unpureinput :: String }
>   deriving (Read,Show)
> 
> 
> -- This works fine, blah blah blah gets outputted
> demo1 = runIO $ ( ( ( ("echo blah blah blah") :: String) -|- ( "cat"
> :: String) ) :: PipeCommand String String )
> 
> 
> -- This is what I want. Specify a pure input string, to be piped into
> another command.
> -- In this example it's cat, which isn't very usefuol.
> -- This would be useful, however, for sending email via sendmail or
> mailx, with variable input piped in.
> -- The result should be that "blah blah blah" is printed from cat,
> just as in demo1.
> demo2 = runIO $ (PureInput "blah blah blah") -|- ( "cat" :: String)
> 
> -- How can/should this be done?
> instance ShellCommand PureInput where
>     fdInvoke (PureInput justAString) ifd ofd closefd forkfunc = undefined
>