CODEWITHSUNDEEP
haskell
SilentDev
SilentDev

Reputation: 22777

"Parse error in pattern" when implementing tree

Here is my code

quadtreeToPic QNode x y w avg Q4(q1 q2 q3 q4) = array ((0,0) (w-1,w-1)) (concat (map quadtreeToPic [q1, q2, q3, q4]))

Basically, a Quadtree is x y w avg QChildren where QChildren is qither Q0 or Q4 Quadtree Quadtree Quadtree Quadtree.

When I do what I tried above, I get this error

Quadtree.hs:13:34: error: Parse error in pattern: q1
   |
13 | quadtreeToPic QNode x y w avg Q4(q1 q2 q3 q4) = array ((0,0) (w-1,w-1)) (concat (map quadtreeToPic [q1, q2, q3, q4])) 
   |                                  ^^^^^^^^^^^

Why is this?

Upvotes: 1

Views: 38

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 477794

The Q4 dataconstructor and the parameters are a single parameter, here, so you need to add brackets including the Q4 data constructor. For example:

quadtreeToPic QNode x y w avg (Q4 q1 q2 q3 q4) = ...

Note that you can use concatMap :: (a -> [b]) -> [a] -> [b] here instead of concat (map ...):

... concatMap quadtreeToPic [q1, q2, q3, q4]

Upvotes: 3

Related Questions