fakeIf :: Bool -> a -> a -> a fakeIf condition ifTrue ifFalse = case condition of True -> ifTrue False -> ifFalse
Controlling actions, revisited
main = do x <- getX putStrLn x getX = do return "My Shangri-La" return "beneath" return "the summer moon" return "I will" return "return" return "again"
main = do putStrLn "Hello, what is your name?" name <- getLine case name of "Simon" -> greatlanguage "John" -> greatlanguage "Phil" -> greatlanguage "Koen" -> putStrLn "I think debugging Haskell is fun." _ -> putStrLn "Sorry, I don't know you." where greatlanguage = putStrLn "I think Haskell is a great programming language."
main will print
"again". Remember that the value of a sequence of IO actions is the same as the value of the last action in the sequence.
getX can also be written as:
getX = do return "again"
or even shorter, as:
getX = return "again"
As a result,
x in the
main function has the value
"again", which will then be written to the screen.