The problem never came up before because we only had one declaration per let expression, and it was always possible to rewrite
let int x = 1, y = 2; x+y
let int x = 1; let int y = 2; x+y
We are pushing the Mint compiler more, and we have discovered another problem with generic methods. Currently, Mint generates a class extending Code<X> with X occurring unbound when this method is called:
public separable abstract <X> Code<X> fun(Code<X> c1, Code<X>
c2, Object... param);
We are looking at making another bugfix soon.