Type and Definition in Haskell

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Above is a question I am having problems with. It asks me to give a type and define a non infix function.

So my approach was to use pattern matching.

The idea was to take two booleans, then go through patterns

 xor :: bool -> bool -> bool xor True True == False xor True False == True xor False True == True xor False False == False

I am getting a compile error.

Parse error: naked expression at top level Perhaps you intended to use TemplateHaskell

Can someone tell me what I am doing wrong here and how I can fix it?

Thanks alot.

willeM_ Van Onsem · Accepted Answer · 2016-05-01 12:27:51Z

please consider reading a basic haskell tutorial - like learnyouahaskell.com.

Types are written with captial cases and the == operator is not assignment but tests for equality

xor :: Bool -> Bool -> Bool xor True True = False xor True False = True xor False True = True xor False False = False

also note that this can be simplified to

xor x y = x /= y

after all it is just checking wether the two values you pass in are not the same.

or even more

xor = (/=)

this style is called point-free, which means if the type signature is clear no parameters are needed (sometimes parameters are referred to as points, for historical/mathematical reasons).

By the way if you wonder what TemplateHaskell is - it is a compiler extension of GHC, which allows you to write code that at compile time creates haskell code - which then is type-checked and compiled again - I think about it as type-safe meta-programming.

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