CODEWITHSUNDEEP
haskellcompiler-errors
Pain
Pain

Reputation: 77

Haskell : Parse error on "|" in otherwise

I am trying to compile the following code, but am getting a "parse error on "|" in the otherwise statement"

Now I am confused as I have used pretty much similar syntax in a few other functions, the only difference being this one takes 2 elements on a list and tries to reconstruct one (FYI: Did not test it yet as I can't compile, so the code in the convertElements line might be wrong!)

I am using spaces, and everything seems aligned. Any idea as to what would be causing it? I moved it to the bottom of the where in case it helped, but alas it did not.

convertElements :: [(String, String, String)] -> [(String, String, String)]
convertElements [] = []
convertElements (x:y:xs) = x: (a,b,c) : convertElements((a,b,c) ++ xs)
                    where b = (getSecond y)
                          c = (getThird y)
                          a | if ((containsDash (getThird x)) > 0) then last (getThird x)
                            | otherwise = (getFirst y)

Upvotes: 0

Views: 1146

Answers (4)

MathematicalOrchid
MathematicalOrchid

Reputation: 62848

You can do

a | ...condition... = ...value...
  | otherwise       = ...value...

or you can do

a = if ...condition... then ...value... else ...value...

But not both. Most particularly, you can't have if without then and else. In Haskell, if isn't a statement, it's an expression (rather like the C ternary operator ?:, if you know of that).

Upvotes: 2

Alexey Romanov
Alexey Romanov

Reputation: 170815

To expand a bit on @ephemient's answer: | can be followed by if ... but that makes if-expression the guard, so the compiler is expecting to see

 a | if ... then ... else ... = ...

But the second | shows up before else does, so you get an error there.

Upvotes: 2

ephemient
ephemient

Reputation: 204926

You were close but not quite with the guard syntax, which does not use the if/then/else keywords.

convertElements :: [(String, String, String)] -> [(String, String, String)]
convertElements [] = []
convertElements (x:y:xs) = x : (a,b,c) : convertElements ((a,b,c) : xs)
  where b = getSecond y
        c = getThird y
        a | containsDash (getThird x) > 0 = last (getThird x)
          | otherwise = getFirst y

Upvotes: 3

Pain
Pain

Reputation: 77

Of course it's when you ask a question that you figure out another way around... I still don't know why I had that error, however the simple solution is to use an "else" instead. Which I've done and can now fix the multitude of errors from this function.

Upvotes: 0

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