Should not allow repeated variable name in pattern

[Matt Giuca]

Mars allows the same variable name to be used multiple times in a pattern, which means the variable will be bound several times. In the current backend (interpret), this binds the variable to its rightmost value.

eg:

x :: Pair(Int, Int)
switch x:
    case Pair(n, n):
        return n

It should be a compiler error. (Hugs gives the error: "Repeated variable "n" in pattern").

[Matt Giuca (mgiuca)]

Fixed in trunk r951.