Confusion about types
In GHC 6.0.1 the following data type definition (for a binary search tree) seems to be invalid. I know I've used this kind of thing before, so whats up. This is the entire file, by the way:
data BST a = Ord a => Leaf | Node a (BST a) (BST a)
Gives an error message :
All of the type variables in the constraint Ord a' are already in scope (at least one must be universally quantified here) When checking the existential context of constructor Leaf'
In the data type declaration for `BST'
I'm confused - where would I put a universal quantification? Does Leaf now need a type declaration and if so what would it be?
Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.4.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | Unknown |
| Architecture | Unknown |