Fix cyclic dependency on std.io
let string = import! std.string
let array = import! std.array
let { wrap } = import! std.applicative
-let { flat_map, ? } = import! std.io
+let { flat_map, wrap } = import! std.io.prim
let { ? } = import! std.int
let { (>=) } = import! std.cmp
let { (+) } = import! std.num
