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I am following a haskell tutorial: http://www.seas.upenn.edu/~cis194/lectures/01-intro.html

I am testing functions in ghci, i got to this part:

hailstone :: Integer -> Integer
hailstone n
  | n `mod` 2 == 0 = n `div` 2
  | otherwise      = 3*n + 1

I have that function in a .hs file, i fire up ghci in the same directory and go :l hailstone.hs

the output is 

Syntax error on 'mod'
    Perhaps you intended to use TemplateHaskell
    In the Template Haskell quotation 'mod'
Failed, modules loaded: none.

did some googling and tried to load this 'templatehaskell' and just ended up with a different set of errors (http://brandon.si/code/working-with-template-haskell-in-ghci/)

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  • ideone.com is happy with this: ideone.com/pe3g9C Commented Jul 3, 2014 at 1:51
  • Typically that happens when mod is written as a top-level form. Is the definition of hailstone the only thing in the file? Commented Jul 3, 2014 at 1:52
  • 6
    Are you by any chance typing " ' " ('mod') as opposed to " ` " (`mod `) ? The latter is correct while the former is not; the backtick is not the same as the single quote. Commented Jul 3, 2014 at 1:54
  • @user2407038 well... this is embarrassing... Commented Jul 3, 2014 at 2:52

1 Answer 1

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As user2407038 correctly suggested in the comments, the problem was that I was using apostrophes (') as opposed to backticks (`), the backtick is not the same as the single quote which I should have been using.

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1 Comment

@David Nono, this is the answer to this question.

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