Haskell: parse error in pattern 3

Question

data Peg = Red | Green | Blue | Yellow | Orange | Purple
    deriving (Show, Eq, Ord)

type Code = [Peg]

data Move = Move Code Int Int
      deriving (Show, Eq)

isConsistent :: Move -> Code -> Bool
isConsistent (move1 code1 num1 num2) code2 = True --parse error here

Relatively new to Haskell. Wondering why I receive the following error message after attempting to load this.

Parse error in pattern: move1

genisage · Accepted Answer · 2015-02-11 00:20:18Z

8

move1 isn't a data constructor (which is what you're allowed to pattern match on) and in fact it can't be since they have to start with uppercase letters. Replace it with the constructor Move from your data declaration and the error should go away.

You will probably still get some warnings like "code1 defined but not used" you can get rid of them by changing the pattern to (Move _ _ _) if you really don't care about the contents.

answered Feb 11, 2015 at 0:20

genisage

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1 Comment

Carcigenicate Over a year ago

Note that if you need a value to refer to the entire piece being pattern matched on, precede it with a name@, ex: move1@(Move code int1 int2). move1 now refers to the entire Move.

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