On Wed, Dec 7, 2011 at 11:46 PM, Brandon Allbery wrote:

On Wed, Dec 7, 2011 at 23:24, Alexej Segeda

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wrote:

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case s of (s == reverse s) -> putStrLn (s ++ " is a palindrome") otherwise -> putStrLn (s ++ " is not a palindrome")

case does pattern matching, not Boolean expressions. (s == reverse s) is not a useful pattern, and in fact is probably a syntax error because ==is not a valid infix constructor.

If you want to do Boolean comparisons in a case, you need to use something like

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case () of () | s == reverse s -> putStrLn "palindrome" _ -> putStrLn "nope"

This is kind of a hack of case, though. I think what the OP was looking for is palindrome :: IO () palindrome = do putStrLn "Type in a word" s <- getLine isPalindrome s isPalindrome word | (word == reverse word) = putStrLn (word ++ " is a palindrome") | otherwise = putStrLn (word ++ " is not a palindrome") amindfv / Tom

Why do you people hate 'if' statements? 2011/12/9 Brandon Allbery

On Thu, Dec 8, 2011 at 15:52, Tom Murphy wrote:

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On Wed, Dec 7, 2011 at 11:46 PM, Brandon Allbery wrote:

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case () of () | s == reverse s -> putStrLn "palindrome" _ -> putStrLn "nope"

This is kind of a hack of case, though. I think what the OP was looking for is

isPalindrome word

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| (word == reverse word) = putStrLn (word ++ " is a palindrome") | otherwise = putStrLn (word ++ " is not a palindrome")

Erm? It's as much of a hack of case as yours is, since the above is actually using case.

-- brandon s allbery allbery.b@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms

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I agree with all that, but in *this *special case, I think that case something of True -> aaaa False -> bbbb is less nice and obvious than if something then aaaa else bbbb 2011/12/9 Brandon Allbery

On Fri, Dec 9, 2011 at 04:16, Yves Parès wrote:

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Why do you people hate 'if' statements?

It's more that the language spec does; if statements, along with a number of other things, desugar to case which is the fundamental conditional construct.

(And more personally, I find the indentation behavior annoying, in that I need to indent then and else more inside something that uses layout; plus the lack of an else if that is aware of being part of a compound means that it "ladders" even more, so I end up switching to case just to keep from ending up on column 200 or something.)

-- brandon s allbery allbery.b@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms

Brandon Allbery wrote:

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case () of   () | s == reverse s -> putStrLn "palindrome"   _                   -> putStrLn "nope"

Tom Murphy wrote:

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This is kind of a hack of case, though. I think what the OP was looking for is  isPalindrome word   | (word == reverse word) = putStrLn (word ++ " is a palindrome")   | otherwise              = putStrLn (word ++ " is not a palindrome")

Erm?  It's as much of a hack of case as yours is, since the above is actually using case.

I agree with Tom here. While it's true that the compiler internally desugars to case, that low-level compiler transformation doesn't have much to do with the best way to write clear code. I find that case often creates code that is more confusing and bug-prone. Except when what I really want to express is pattern matching, *and* there is some specific reason here why I don't want to use a named function in a let or where binding. Altogether, it doesn't come up very often for me. And even for styles that use case more than I do, certainly there is room to call the use of the "case ()" idiom a hack. (Even though I'll admit that I do use it sometimes.) Regards, Yitz