I have a TernaryTree type.
data TernaryTree a = Node a (TernaryTree a) (TernaryTree a) (TernaryTree a) | Nil deriving (Eq, Show)
Given a list, I want to be able to apply the Node constructor to it, e.g.
Node v [t1, t2, t3] -- error
The above is, of course, invalid.
There are good ways through pattern matching to do the opposite, e.g
let Node v t1 t2 t3 = parent in [t1,t2,t3]
but I could not find a simple solution to my problem other than writing a function, e.g.
makeNode v lst@[t1,t2,t3] = Node v t1 t2 t3
Even if I had the function, it is not flexible, e.g. it cannot do this,
Node v t1 [t2, t3] -- error
I now require another function.
I could add further constructors to the type for this but it seems to me that there must be a simpler way.
The type of the operation that would do what I want is
[a] -> a a a
which, I think, should be undefined.
This seems so simple a requirement that I am sure there is an easy built-in way to do this but I just cannot find it.
Is there a built-in way to use a constructor on a list?
