[Haskell-cafe] monad question
p.turner at computer.org
Sun Sep 19 20:27:11 EDT 2004
On 2004 September 19 Sunday 13:40, Andrew Harris wrote:
> handleSeeRecord :: [SeeObjInfo_type] -> RobotState -> IO (RobotState, ())
> handleSeeRecord seeobjlist p = do flaglist <- return (morphToList
> flagFinder seeobjlist)
> balllist <- return (morphToList
> ballFinder seeobjlist)
> friendlist <- return (morphToList
> friendFinder seeobjlist)
> foelist <- return (morphToList
> foeFinder seeobjlist)
> Robot e <- return (assign_flags
> (flagSpread flaglist))
> Robot f <- return (assign_ball balllist)
> Robot g <- return (assign_friends
> friendlist) Robot h <- return (assign_foes foelist) (r', ()) <- e p
> (r'', ()) <- f r'
> (r''', ()) <- g r''
> h r'''
What you're looking for is something like
handleSeeRecord :: [SeeObjInfo_type] -> Robot ()
handleSeeRecord seeobjlist = do
let flaglist = morphToList flagFinder seeobjlist
let balllist = morphToList ballFinder seeobjlist
let friendlist = morphToList friendFinder seeobjlist
let foelist = morphToList foeFinder seeobjlist
assign_flags (flagSpread flaglist)
This uses the 'do' notation with the Robot monad, whose operations are closer
to what the code is doing than the IO monad. Also, replacing 'return' with
'let' removes the unnecessary reference to the monad.
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